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Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blue-green algae, although they are not usually scientifically classified as algae. They appear to have originated in a freshwater or terrestrial environment. Sericytochromatia, the proposed name of the
paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
and most basal group, is the ancestor of both the non-photosynthetic group Melainabacteria and the photosynthetic cyanobacteria, also called Oxyphotobacteria. Cyanobacteria use
photosynthetic pigment A photosynthetic pigment (accessory pigment; chloroplast pigment; antenna pigment) is a pigment that is present in chloroplasts or photosynthetic bacteria and captures the light energy necessary for photosynthesis. List of photosynthetic pi ...
s, such as carotenoids, phycobilins, and various forms of chlorophyll, which absorb energy from light. Unlike
heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...
ic prokaryotes, cyanobacteria have internal membranes. These are flattened sacs called thylakoids where photosynthesis is performed. Phototrophic eukaryotes such as green plants perform photosynthesis in plastids that are thought to have their ancestry in cyanobacteria, acquired long ago via a process called endosymbiosis. These endosymbiotic cyanobacteria in eukaryotes then evolved and differentiated into specialized organelles such as chloroplasts,
chromoplasts Chromoplasts are plastids, heterogeneous organelles responsible for pigment synthesis and storage in specific photosynthetic eukaryotes. It is thought that like all other plastids including chloroplasts and leucoplasts they are descended from sym ...
, etioplasts, and leucoplasts, collectively known as plastids. Cyanobacteria are the first organisms known to have produced oxygen. By producing and releasing oxygen as a byproduct of photosynthesis, cyanobacteria are thought to have converted the early oxygen-poor, reducing atmosphere into an oxidizing one, causing the Great Oxidation Event and the "rusting of the Earth", which dramatically changed the composition of the Earth's life forms. The cyanobacteria '' Synechocystis'' and '' Cyanothece'' are important model organisms with potential applications in biotechnology for bioethanol production, food colorings, as a source of human and animal food, dietary supplements and raw materials. Cyanobacteria produce a range of toxins known as cyanotoxins that can pose a danger to humans and animals.


Overview

Cyanobacteria are a very large and diverse phylum of photoautotrophic
prokaryote A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Con ...
s. They are defined by their unique combination of pigments and their ability to perform
oxygenic photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
. They often live in colonial aggregates that can take on a multitude of forms. Of particular interest are the filamentous species, which often dominate the upper layers of microbial mats found in extreme environments such as
hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...
s, hypersaline water, deserts and the polar regions, but are also widely distributed in more mundane environments as well. Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
Cyanobacteria are a group of photosynthetic bacteria evolutionarily optimized for environmental conditions of low oxygen. Some species are nitrogen-fixing and live in a wide variety of moist soils and water, either freely or in a symbiotic relationship with plants or lichen-forming
fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately fr ...
(as in the lichen genus '' Peltigera''). They range from unicellular to
filamentous The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filamen ...
and include colonial species. Colonies may form filaments, sheets, or even hollow spheres. Cyanobacteria are globally widespread photosynthetic prokaryotes and are major contributors to global biogeochemical cycles. They are the only oxygenic photosynthetic prokaryotes, and prosper in diverse and extreme habitats. They are among the oldest organisms on Earth with fossil records dating back 3.5 billion years. Since then, cyanobacteria have been essential players in the Earth's ecosystems. Planktonic cyanobacteria are a fundamental component of marine food webs and are major contributors to global
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...
and nitrogen fluxes. Some cyanobacteria form harmful algal blooms causing the disruption of aquatic ecosystem services and intoxication of wildlife and humans by the production of powerful toxins ( cyanotoxins) such as microcystins,
saxitoxin Saxitoxin (STX) is a potent neurotoxin and the best-known paralytic shellfish toxin (PST). Ingestion of saxitoxin by humans, usually by consumption of shellfish contaminated by toxic algal blooms, is responsible for the illness known as paralyti ...
, and
cylindrospermopsin Cylindrospermopsin (abbreviated to CYN, or CYL) is a cyanotoxin produced by a variety of freshwater cyanobacteria. CYN is a polycyclic uracil derivative containing guanidino and sulfate groups. It is also zwitterionic, making it highly water ...
. Nowadays, cyanobacterial blooms pose a serious threat to aquatic environments and public health, and are increasing in frequency and magnitude globally. Cyanobacteria are ubiquitous in marine environments and play important roles as primary producers. Marine phytoplankton today contribute almost half of the Earth's total primary production. Within the cyanobacteria, only a few lineages colonized the open-ocean (i.e., ''
Crocosphaera The Aphanothecaceae is a family of cyanobacteria Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly ...
'' and relatives,
cyanobacterium UCYN-A ''Candidatus'' ''Atelocyanobacterium thalassa'', also referred to as UCYN-A, is a diazotrophic species of cyanobacteria commonly found in measurable quantities throughout the world's oceans and some seas. Members of ''A. thalassa'' are spheroid ...
, '' Trichodesmium'', as well as '' Prochlorococcus'' and '' Synechococcus''). From these lineages, nitrogen fixing cyanobacteria are particularly important because they exert a control on primary productivity and the export of organic carbon to the deep ocean, by converting nitrogen gas into ammonium, which is later used to make amino acids and proteins. Marine picocyanobacteria (i.e., ''Prochlorococcus'' and ''Synechococcus'') numerically dominate most phytoplankton assemblages in modern oceans contributing importantly to primary productivity. While some planktonic cyanobacteria are unicellular and free living cells (e.g., ''Crocosphaera'', ''Prochlorococcus'', ''Synechococcus''), others have established symbiotic relationships with haptophyte algae, such as
coccolithophore Coccolithophores, or coccolithophorids, are single celled organisms which are part of the phytoplankton, the autotrophic (self-feeding) component of the plankton community. They form a group of about 200 species, and belong either to the king ...
s. Amongst the filamentous forms, ''Trichodesmium'' are free-living and form aggregates. However, filamentous heterocyst-forming cyanobacteria (e.g., '' Richelia'', '' Calothrix'') are found in association with diatoms such as ''Hemiaulus'', ''Rhizosolenia'' and ''
Chaetoceros ''Chaetoceros'' is probably the largest genus of marine planktonic diatoms with approximately 400 species described, although many of these descriptions are no longer valid. It is often very difficult to distinguish between different ''Chaeto ...
''. Marine cyanobacteria include the smallest known photosynthetic organisms. The smallest of all, '' Prochlorococcus'', is just 0.5 to 0.8 micrometres across. In terms of individual numbers, ''Prochlorococcus'' is possibly the most plentiful species on Earth: a single millilitre of surface seawater can contain 100,000 cells or more. Worldwide there are estimated to be several
octillion Two naming scales for large numbers have been used in English and other European languages since the early modern era: the long and short scales. Most English variants use the short scale today, but the long scale remains dominant in many non-Eng ...
(1027) individuals. ''Prochlorococcus'' is ubiquitous between 40°N and 40°S and dominates in the oligotrophic (nutrient poor) regions of the oceans. The bacterium accounts for about 20% of the oxygen in the Earth's atmosphere.


Morphology

Cyanobacteria are variable in morphology, ranging from unicellular and
filamentous The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filamen ...
to colonial forms. Filamentous forms exhibit functional cell differentiation such as heterocysts (for nitrogen fixation),
akinetes An akinete is an enveloped, thick-walled, non-motile, dormant cell formed by filamentous, heterocyst-forming cyanobacteria under the order Nostocales and Stigonematales. Akinetes are resistant to cold and desiccation. They also accumulate and stor ...
(resting stage cells), and hormogonia (reproductive, motile filaments). These, together with the intercellular connections they possess, are considered the first signs of multicellularity. Many cyanobacteria form motile filaments of cells, called hormogonia, that travel away from the main biomass to bud and form new colonies elsewhere. The cells in a hormogonium are often thinner than in the vegetative state, and the cells on either end of the motile chain may be tapered. To break away from the parent colony, a hormogonium often must tear apart a weaker cell in a filament, called a necridium. Some filamentous species can differentiate into several different cell types: * Vegetative cells – the normal, photosynthetic cells that are formed under favorable growing conditions * Akinetes – climate-resistant spores that may form when environmental conditions become harsh * Thick-walled heterocysts – which contain the enzyme nitrogenase vital for
nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
in an anaerobic environment due to its sensitivity to oxygen. Each individual cell (each single cyanobacterium) typically has a thick, gelatinous cell wall. They lack flagella, but hormogonia of some species can move about by gliding along surfaces. Many of the multicellular filamentous forms of '' Oscillatoria'' are capable of a waving motion; the filament oscillates back and forth. In water columns, some cyanobacteria float by forming gas vesicles, as in archaea. These vesicles are not organelles as such. They are not bounded by lipid membranes, but by a protein sheath.


Nitrogen fixation

Some cyanobacteria can fix atmospheric
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
in anaerobic conditions by means of specialized cells called heterocysts. Heterocysts may also form under the appropriate environmental conditions (anoxic) when fixed nitrogen is scarce. Heterocyst-forming species are specialized for nitrogen fixation and are able to fix nitrogen gas into
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous ...
(), nitrites () or nitrates (), which can be absorbed by plants and converted to protein and nucleic acids (atmospheric nitrogen is not bioavailable to plants, except for those having endosymbiotic
nitrogen-fixing bacteria Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
, especially the family
Fabaceae The Fabaceae or Leguminosae,International Code of Nomenc ...
, among others). Free-living cyanobacteria are present in the water of rice paddies, and cyanobacteria can be found growing as epiphytes on the surfaces of the green alga, '' Chara'', where they may fix nitrogen. Cyanobacteria such as ''
Anabaena ''Anabaena'' is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern. They are one of four genera of cyan ...
'' (a symbiont of the aquatic fern ''
Azolla ''Azolla'' (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like other typical ferns but more rese ...
'') can provide rice plantations with biofertilizer.


Photosynthesis


Carbon fixation

Cyanobacteria use the energy of
sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when ...
to drive
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
, a process where the energy of light is used to synthesize
organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. Th ...
s from carbon dioxide. Because they are aquatic organisms, they typically employ several strategies which are collectively known as a " concentrating mechanism" to aid in the acquisition of inorganic carbon ( or
bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochemi ...
). Among the more specific strategies is the widespread prevalence of the bacterial microcompartments known as carboxysomes, which co-operate with active transporters of CO2 and bicarbonate, in order to accumulate bicarbonate into the cytoplasm of the cell. Carboxysomes are icosahedral structures composed of hexameric shell proteins that assemble into cage-like structures that can be several hundreds of nanometres in diameter. It is believed that these structures tether the -fixing enzyme, RuBisCO, to the interior of the shell, as well as the enzyme
carbonic anhydrase The carbonic anhydrases (or carbonate dehydratases) () form a family of enzymes that catalyze the interconversion between carbon dioxide and water and the dissociated ions of carbonic acid (i.e. bicarbonate and hydrogen ions). The active sit ...
, using
metabolic channeling Substrate channeling is the passing of the intermediary metabolic product of one enzyme directly to another enzyme or active site without its release into solution. When several consecutive enzymes of a metabolic pathway channel substrates between ...
to enhance the local concentrations and thus increase the efficiency of the RuBisCO enzyme.


Electron transport

In contrast to
purple bacteria Purple bacteria or purple photosynthetic bacteria are Gram-negative proteobacteria that are phototrophic, capable of producing their own food via photosynthesis. They are pigmented with bacteriochlorophyll ''a'' or ''b'', together with variou ...
and other bacteria performing anoxygenic photosynthesis, thylakoid membranes of cyanobacteria are not continuous with the plasma membrane but are separate compartments. The photosynthetic machinery is embedded in the thylakoid membranes, with phycobilisomes acting as light-harvesting antennae attached to the membrane, giving the green pigmentation observed (with wavelengths from 450 nm to 660 nm) in most cyanobacteria. While most of the high-energy
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...
s derived from water are used by the cyanobacterial cells for their own needs, a fraction of these electrons may be donated to the external environment via
electrogenic Electroreception and electrogenesis are the closely-related biological abilities to perceive electrical stimuli and to generate electric fields. Both are used to locate prey; stronger electric discharges are used in a few groups of fishes to stu ...
activity.


Respiration

Respiration in cyanobacteria can occur in the thylakoid membrane alongside photosynthesis, with their photosynthetic electron transport sharing the same compartment as the components of respiratory electron transport. While the goal of photosynthesis is to store energy by building carbohydrates from CO2, respiration is the reverse of this, with carbohydrates turned back into CO2 accompanying energy release. Cyanobacteria appear to separate these two processes with their plasma membrane containing only components of the respiratory chain, while the thylakoid membrane hosts an interlinked respiratory and photosynthetic electron transport chain. Cyanobacteria use electrons from
succinate dehydrogenase Succinate dehydrogenase (SDH) or succinate-coenzyme Q reductase (SQR) or respiratory complex II is an enzyme complex, found in many bacterial cells and in the inner mitochondrial membrane of eukaryotes. It is the only enzyme that participates ...
rather than from NADPH for respiration. Cyanobacteria only respire during the night (or in the dark) because the facilities used for electron transport are used in reverse for photosynthesis while in the light.


Electron transport chain

Many cyanobacteria are able to reduce nitrogen and carbon dioxide under aerobic conditions, a fact that may be responsible for their evolutionary and ecological success. The water-oxidizing photosynthesis is accomplished by coupling the activity of
photosystem Photosystems are functional and structural units of protein complexes involved in photosynthesis. Together they carry out the primary photochemistry of photosynthesis: the absorption of light and the transfer of energy and electrons. Photosy ...
(PS) II and I (
Z-scheme Light-dependent reactions is jargon for certain photochemical reactions that are involved in photosynthesis, the main process by which plants acquire energy. There are two light dependent reactions, the first occurs at photosystem II (PSII) and ...
). In contrast to green sulfur bacteria which only use one photosystem, the use of water as an electron donor is energetically demanding, requiring two photosystems. Attached to the thylakoid membrane, phycobilisomes act as light-harvesting antennae for the photosystems. The phycobilisome components ( phycobiliproteins) are responsible for the blue-green pigmentation of most cyanobacteria. The variations on this theme are due mainly to carotenoids and phycoerythrins that give the cells their red-brownish coloration. In some cyanobacteria, the color of light influences the composition of the phycobilisomes. In green light, the cells accumulate more phycoerythrin, which absorbs green light, whereas in red light they produce more phycocyanin which absorbs red. Thus, these bacteria can change from brick-red to bright blue-green depending on whether they are exposed to green light or to red light. This process of "complementary chromatic adaptation" is a way for the cells to maximize the use of available light for photosynthesis. A few genera lack phycobilisomes and have chlorophyll b instead ('' Prochloron'', '' Prochlorococcus'', ''Prochlorothrix''). These were originally grouped together as the prochlorophytes or chloroxybacteria, but appear to have developed in several different lines of cyanobacteria. For this reason, they are now considered as part of the cyanobacterial group.


Metabolism

In general, photosynthesis in cyanobacteria uses water as an electron donor and produces
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...
as a byproduct, though some may also use hydrogen sulfide a process which occurs among other photosynthetic bacteria such as the purple sulfur bacteria.
Carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
is reduced to form
carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may o ...
s via the Calvin cycle. The large amounts of oxygen in the atmosphere are considered to have been first created by the activities of ancient cyanobacteria. They are often found as symbionts with a number of other groups of organisms such as fungi (lichens),
coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and se ...
s, pteridophytes (''
Azolla ''Azolla'' (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae. They are extremely reduced in form and specialized, looking nothing like other typical ferns but more rese ...
''), angiosperms ('' Gunnera''), etc. There are some groups capable of heterotrophic growth, while others are parasitic, causing diseases in invertebrates or algae (e.g., the black band disease).


Ecology

Cyanobacteria can be found in almost every terrestrial and
aquatic habitat Marine biology is the scientific study of the biology of marine life, organisms in the sea. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies s ...
 –
ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wor ...
s, fresh water, damp soil, temporarily moistened rocks in deserts, bare rock and soil, and even Antarctic rocks. They can occur as planktonic cells or form
phototrophic biofilms Phototrophic biofilms are microbial communities generally comprising both phototrophic microorganisms, which use light as their energy source, and chemoheterotrophs. Thick laminated multilayered phototrophic biofilms are usually referred to as m ...
. They are found inside stones and shells (in endolithic ecosystems). A few are endosymbionts in lichens, plants, various
protist A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the e ...
s, or sponges and provide energy for the host. Some live in the fur of
sloth Sloths are a group of Neotropical xenarthran mammals constituting the suborder Folivora, including the extant arboreal tree sloths and extinct terrestrial ground sloths. Noted for their slowness of movement, tree sloths spend most of their l ...
s, providing a form of
camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...
. Aquatic cyanobacteria are known for their extensive and highly visible blooms that can form in both freshwater and marine environments. The blooms can have the appearance of blue-green paint or scum. These blooms can be
toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a sub ...
, and frequently lead to the closure of recreational waters when spotted.
Marine bacteriophage Marine viruses are defined by their habitat as viruses that are found in marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. Viruses are small infectious agents that can only replicate i ...
s are significant parasites of unicellular marine cyanobacteria. Cyanobacterial growth is favoured in ponds and lakes where waters are calm and have little turbulent mixing. Their lifecycles are disrupted when the water naturally or artificially mixes from churning currents caused by the flowing water of streams or the churning water of fountains. For this reason blooms of cyanobacteria seldom occur in rivers unless the water is flowing slowly. Growth is also favoured at higher temperatures which enable '' Microcystis'' species to outcompete
diatoms A diatom (Neo-Latin ''diatoma''), "a cutting through, a severance", from el, διάτομος, diátomos, "cut in half, divided equally" from el, διατέμνω, diatémno, "to cut in twain". is any member of a large group comprising sev ...
and green algae, and potentially allow development of toxins. Based on environmental trends, models and observations suggest cyanobacteria will likely increase their dominance in aquatic environments. This can lead to serious consequences, particularly the contamination of sources of
drinking water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, ...
. Researchers including Linda Lawton at Robert Gordon University, have developed techniques to study these. Cyanobacteria can interfere with
water treatment Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, inc ...
in various ways, primarily by plugging filters (often large beds of sand and similar media) and by producing cyanotoxins, which have the potential to cause serious illness if consumed. Consequences may also lie within fisheries and waste management practices. Anthropogenic
eutrophication Eutrophication is the process by which an entire body of water, or parts of it, becomes progressively enriched with minerals and nutrients, particularly nitrogen and phosphorus. It has also been defined as "nutrient-induced increase in phyt ...
, rising temperatures, vertical stratification and increased atmospheric carbon dioxide are contributors to cyanobacteria increasing dominance of aquatic ecosystems. Cyanobacteria have been found to play an important role in terrestrial habitats. It has been widely reported that cyanobacteria soil crusts help to stabilize soil to prevent
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...
and retain water. An example of a cyanobacterial species that does so is ''Microcoleus vaginatus''. ''M. vaginatus'' stabilizes soil using a polysaccharide sheath that binds to sand particles and absorbs water. Some of these organisms contribute significantly to global ecology and the oxygen cycle. The tiny marine cyanobacterium '' Prochlorococcus'' was discovered in 1986 and accounts for more than half of the photosynthesis of the open ocean. Circadian rhythms were once thought to only exist in eukaryotic cells but many cyanobacteria display a
bacterial circadian rhythm Bacterial circadian rhythms, like other circadian rhythms, are endogenous "biological clocks" that have the following three characteristics: (a) in constant conditions (i.e. constant temperature and either constant light or constant darkness ) they ...
.
"Cyanobacteria are arguably the most successful group of microorganisms on earth. They are the most genetically diverse; they occupy a broad range of habitats across all latitudes, widespread in freshwater, marine, and terrestrial ecosystems, and they are found in the most extreme niches such as hot springs, salt works, and hypersaline bays. Photoautotrophic, oxygen-producing cyanobacteria created the conditions in the planet's early atmosphere that directed the evolution of aerobic metabolism and eukaryotic photosynthesis. Cyanobacteria fulfill vital ecological functions in the world's oceans, being important contributors to global carbon and nitrogen budgets." – Stewart and Falconer


Cyanobionts

Some cyanobacteria, the so-called cyanobionts (cyanobacterial symbionts), have a symbiotic relationship with other organisms, both unicellular and multicellular. As illustrated on the right, there are many examples of cyanobacteria interacting symbiotically with land plants. Cyanobacteria can enter the plant through the
stomata In botany, a stoma (from Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. The pore is b ...
and colonize the intercellular space, forming loops and intracellular coils. ''
Anabaena ''Anabaena'' is a genus of filamentous cyanobacteria that exist as plankton. They are known for nitrogen-fixing abilities, and they form symbiotic relationships with certain plants, such as the mosquito fern. They are one of four genera of cyan ...
'' spp. colonize the roots of wheat and cotton plants. '' Calothrix'' sp. has also been found on the root system of wheat.
Monocot Monocotyledons (), commonly referred to as monocots, (Lilianae '' sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one ...
s, such as wheat and rice, have been colonised by ''
Nostoc ''Nostoc'', also known as star jelly, troll’s butter, spit of moon, fallen star, witch's butter (not to be confused with the fungi commonly known as witches' butter), and witch’s jelly, is the most common genus of cyanobacteria found in var ...
'' spp., In 1991, Ganther and others isolated diverse
heterocystous Heterocysts or heterocytes are specialized nitrogen-fixing cells formed during nitrogen starvation by some filamentous cyanobacteria, such as ''Nostoc punctiforme'', ''Cylindrospermum stagnale'', and ''Anabaena sphaerica''. They fix nitrogen from ...
nitrogen-fixing cyanobacteria, including ''Nostoc'', ''Anabaena'' and '' Cylindrospermum'', from plant root and soil. Assessment of wheat seedling roots revealed two types of association patterns: loose colonization of root hair by ''Anabaena'' and tight colonization of the root surface within a restricted zone by ''Nostoc''. The relationships between cyanobionts (cyanobacterial symbionts) and protistan hosts are particularly noteworthy, as some nitrogen-fixing cyanobacteria (
diazotroph Diazotrophs are bacteria and archaea that fix gaseous nitrogen in the atmosphere into a more usable form such as ammonia. A diazotroph is a microorganism that is able to grow without external sources of fixed nitrogen. Examples of organisms tha ...
s) play an important role in
primary production In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ...
, especially in nitrogen-limited oligotrophic oceans. Cyanobacteria, mostly
pico- A metric prefix is a unit prefix that precedes a basic unit of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic. Each prefix has a unique symbol that is prepended to any unit symbol. The pr ...
sized '' Synechococcus'' and '' Prochlorococcus'', are ubiquitously distributed and are the most abundant photosynthetic organisms on Earth, accounting for a quarter of all carbon fixed in marine ecosystems. In contrast to free-living marine cyanobacteria, some cyanobionts are known to be responsible for nitrogen fixation rather than carbon fixation in the host. However, the physiological functions of most cyanobionts remain unknown. Cyanobionts have been found in numerous protist groups, including dinoflagellates, tintinnids, radiolarians, amoebae, diatoms, and haptophytes. Among these cyanobionts, little is known regarding the nature (e.g., genetic diversity, host or cyanobiont specificity, and cyanobiont seasonality) of the symbiosis involved, particularly in relation to dinoflagellate host.


Collective behaviour

Some cyanobacteria – even single-celled ones – show striking collective behaviours and form colonies (or blooms) that can float on water and have important ecological roles. For instance, billions of years ago, communities of marine Paleoproterozoic cyanobacteria could have helped create the biosphere as we know it by burying carbon compounds and allowing the initial build-up of oxygen in the atmosphere. On the other hand, toxic cyanobacterial blooms are an increasing issue for society, as their toxins can be harmful to animals. Extreme blooms can also deplete water of oxygen and reduce the penetration of sunlight and visibility, thereby compromising the feeding and mating behaviour of light-reliant species. As shown in the diagram on the right, bacteria can stay in suspension as individual cells, adhere collectively to surfaces to form biofilms, passively sediment, or flocculate to form suspended aggregates. Cyanobacteria are able to produce sulphated polysaccharides (yellow haze surrounding clumps of cells) that enable them to form floating aggregates. In 2021, Maeda et al. discovered that oxygen produced by cyanobacteria becomes trapped in the network of polysaccharides and cells, enabling the microorganisms to form buoyant blooms. It is thought that specific protein fibres known as
pili Pili may refer to: Common names of plants * '' Canarium ovatum'', a Philippine tree that is a source of the pili nut * ''Heteropogon contortus'', a Hawaiian grass used to thatch structures Places * Pili, Camarines Sur, is a municipality in the ...
(represented as lines radiating from the cells) may act as an additional way to link cells to each other or onto surfaces. Some cyanobacteria also use sophisticated intracellular gas vesicles as floatation aids. The diagram on the left above shows a proposed model of microbial distribution, spatial organization, carbon and O2 cycling in clumps and adjacent areas. (a) Clumps contain denser cyanobacterial filaments and heterotrophic microbes. The initial differences in density depend on cyanobacterial motility and can be established over short timescales. Darker blue color outside of the clump indicates higher oxygen concentrations in areas adjacent to clumps. Oxic media increase the reversal frequencies of any filaments that begin to leave the clumps, thereby reducing the net migration away from the clump. This enables the persistence of the initial clumps over short timescales; (b) Spatial coupling between photosynthesis and respiration in clumps. Oxygen produced by cyanobacteria diffuses into the overlying medium or is used for aerobic respiration. Dissolved inorganic carbon (DIC) diffuses into the clump from the overlying medium and is also produced within the clump by respiration. In oxic solutions, high O2 concentrations reduce the efficiency of CO2 fixation and result in the excretion of glycolate. Under these conditions, clumping can be beneficial to cyanobacteria if it stimulates the retention of carbon and the assimilation of inorganic carbon by cyanobacteria within clumps. This effect appears to promote the accumulation of particulate organic carbon (cells, sheaths and heterotrophic organisms) in clumps. It has been unclear why and how cyanobacteria form communities. Aggregation must divert resources away from the core business of making more cyanobacteria, as it generally involves the production of copious quantities of extracellular material. In addition, cells in the centre of dense aggregates can also suffer from both shading and shortage of nutrients. So, what advantage does this communal life bring for cyanobacteria? New insights into how cyanobacteria form blooms have come from a 2021 study on the cyanobacterium '' Synechocystis''. These use a set of genes that regulate the production and export of sulphated polysaccharides, chains of sugar molecules modified with sulphate groups that can often be found in marine algae and animal tissue. Many bacteria generate extracellular polysaccharides, but sulphated ones have only been seen in cyanobacteria. In ''Synechocystis'' these sulphated polysaccharide help the cyanobacterium form buoyant aggregates by trapping oxygen bubbles in the slimy web of cells and polysaccharides. Previous studies on ''Synechocystis'' have shown type IV pili, which decorate the surface of cyanobacteria, also play a role in forming blooms. These retractable and adhesive protein fibres are important for motility, adhesion to substrates and DNA uptake. The formation of blooms may require both type IV pili and Synechan – for example, the pili may help to export the polysaccharide outside the cell. Indeed, the activity of these protein fibres may be connected to the production of extracellular polysaccharides in filamentous cyanobacteria. A more obvious answer would be that pili help to build the aggregates by binding the cells with each other or with the extracellular polysaccharide. As with other kinds of bacteria, certain components of the pili may allow cyanobacteria from the same species to recognise each other and make initial contacts, which are then stabilised by building a mass of extracellular polysaccharide. The bubble flotation mechanism identified by Maeda et al. joins a range of known strategies that enable cyanobacteria to control their buoyancy, such as using gas vesicles or accumulating carbohydrate ballasts. Type IV pili on their own could also control the position of marine cyanobacteria in the water column by regulating viscous drag. Extracellular polysaccharide appears to be a multipurpose asset for cyanobacteria, from floatation device to food storage, defence mechanism and mobility aid.


Cellular death

One of the most critical processes determining cyanobacterial eco-physiology is cellular death. Evidence supports the existence of controlled cellular demise in cyanobacteria, and various forms of cell death have been described as a response to biotic and abiotic stresses. However, cell death research in cyanobacteria is a relatively young field and understanding of the underlying mechanisms and molecular machinery underpinning this fundamental process remains largely elusive. However, reports on cell death of marine and freshwater cyanobacteria indicate this process has major implications for the ecology of microbial communities/Agustí, S. (2004)
"Viability and niche segregation of ''Prochlorococcus'' and ''Synechococcus'' cells across the Central Atlantic Ocean."
Accessed: 30 July 2021).
Different forms of cell demise have been observed in cyanobacteria under several stressful conditions, and cell death has been suggested to play a key role in developmental processes, such as akinete and heterocyst differentiation.


Cyanophages

Cyanophages are viruses that infect cyanobacteria. Cyanophages can be found in both freshwater and marine environments. Marine and freshwater cyanophages have icosahedral heads, which contain double-stranded DNA, attached to a tail by connector proteins. The size of the head and tail vary among species of cyanophages. Cyanophages like other bacteriophages rely on Brownian motion to collide with bacteria, and then use receptor binding proteins to recognize cell surface proteins, which leads to adherence. Viruses with contractile tails then rely on receptors found on their tails to recognize highly conserved proteins on the surface of the host cell. Cyanophages infect a wide range of cyanobacteria and are key regulators of the cyanobacterial populations in aquatic environments, and may aid in the prevention of cyanobacterial blooms in freshwater and marine ecosystems. These blooms can pose a danger to humans and other animals, particularly in eutrophic freshwater lakes. Infection by these viruses is highly prevalent in cells belonging to '' Synechococcus'' spp. in marine environments, where up to 5% of cells belonging to marine cyanobacterial cells have been reported to contain mature phage particles. The first cyanophage, LPP-1, was discovered in 1963. Cyanophages are classified within the bacteriophage families '' Myoviridae'' (e.g. AS-1, N-1), '' Podoviridae'' (e.g. LPP-1) and '' Siphoviridae'' (e.g. S-1).Sarma TA. 'Cyanophages' in ''Handbook of Cyanobacteria'' ( CRC Press; 2012) ()


Movement

It has long been known that filamentous cyanobacteria perform surface motions, and that these movements result from type IV pili. Additionally, '' Synechococcus'', a marine cyanobacteria, is known to swim at a speed of 25 μm/s by a mechanism different to that of bacterial flagella. Formation of waves on the cyanobacteria surface is thought to push surrounding water backwards. Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
Cells are known to be motile by a gliding method and a novel uncharacterized, nonphototactic swimming method that does not involve flagellar motion. Many species of cyanobacteria are capable of gliding. Gliding is a form of cell movement that differs from crawling or swimming in that it does not rely on any obvious external organ or change in cell shape and it occurs only in the presence of a substrate. Gliding in filamentous cyanobacteria appears to be powered by a "slime jet" mechanism, in which the cells extrude a gel that expands quickly as it hydrates providing a propulsion force, although some unicellular cyanobacteria use type IV pili for gliding. Cyanobacteria have strict light requirements. Too little light can result in insufficient energy production, and in some species may cause the cells to resort to heterotrophic respiration. Too much light can inhibit the cells, decrease photosynthesis efficiency and cause damage by bleaching. UV radiation is especially deadly for cyanobacteria, with normal solar levels being significantly detrimental for these microorganisms in some cases. Filamentous cyanobacteria that live in microbial mats often migrate vertically and horizontally within the mat in order to find an optimal niche that balances their light requirements for photosynthesis against their sensitivity to photodamage. For example, the filamentous cyanobacteria '' Oscillatoria'' sp. and '' Spirulina subsalsa'' found in the hypersaline benthic mats of Guerrero Negro, Mexico migrate downwards into the lower layers during the day in order to escape the intense sunlight and then rise to the surface at dusk. In contrast, the population of '' Microcoleus chthonoplastes'' found in hypersaline mats in Camargue, France migrate to the upper layer of the mat during the day and are spread homogenously through the mat at night. An in vitro experiment using P. uncinatum also demonstrated this species' tendency to migrate in order to avoid damaging radiation. These migrations are usually the result of some sort of photomovement, although other forms of taxis can also play a role. Photomovement – the modulation of cell movement as a function of the incident light – is employed by the cyanoabacteria as a means to find optimal light conditions in their environment. There are three types of photomovement: photokinesis, phototaxis and photophobic responses. Photokinetic microorganisms modulate their gliding speed according to the incident light intensity. For example, the speed with which Phormidium autumnale glides increases linearly with the incident light intensity. Phototactic microorganisms move according to the direction of the light within the environment, such that positively phototactic species will tend to move roughly parallel to the light and towards the light source. Species such as '' Phormidium uncinatum'' cannot steer directly towards the light, but rely on random collisions to orient themselves in the right direction, after which they tend to move more towards the light source. Others, such as '' Anabaena variabilis'', can steer by bending the trichome. Finally, photophobic microorganisms respond to spatial and temporal light gradients. A step-up photophobic reaction occurs when an organism enters a brighter area field from a darker one and then reverses direction, thus avoiding the bright light. The opposite reaction, called a step-down reaction, occurs when an organism enters a dark area from a bright area and then reverses direction, thus remaining in the light.


Evolution


Earth history

Stromatolites are layered biochemical
accretion Accretion may refer to: Science * Accretion (astrophysics), the formation of planets and other bodies by collection of material through gravity * Accretion (meteorology), the process by which water vapor in clouds forms water droplets around nucl ...
ary
structure A structure is an arrangement and organization of interrelated elements in a material object or system, or the object or system so organized. Material structures include man-made objects such as buildings and machines and natural objects such a ...
s formed in shallow water by the trapping, binding, and cementation of sedimentary grains by
biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular po ...
s ( microbial mats) of
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
s, especially cyanobacteria. During the
Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of th ...
, stromatolite communities of microorganisms grew in most marine and non-marine environments in the photic zone. After the Cambrian explosion of marine animals, grazing on the stromatolite mats by herbivores greatly reduced the occurrence of the stromatolites in marine environments. Since then, they are found mostly in hypersaline conditions where grazing invertebrates cannot live (e.g. Shark Bay, Western Australia). Stromatolites provide ancient records of life on Earth by fossil remains which date from 3.5 Ga ago. the oldest undisputed evidence of cyanobacteria is from 2.1 Ga ago, but there is some evidence for them as far back as 2.7 Ga ago. Oxygen concentrations in the atmosphere remained around or below 1% of today's level until 2.4 Ga ago (the Great Oxygenation Event). The rise in oxygen may have caused a fall in the concentration of atmospheric methane, and triggered the Huronian glaciation from around 2.4 to 2.1 Ga ago. In this way, cyanobacteria may have killed off much of the other bacteria of the time. Oncolites are sedimentary structures composed of oncoids, which are layered structures formed by cyanobacterial growth. Oncolites are similar to stromatolites, but instead of forming columns, they form approximately spherical structures that were not attached to the underlying substrate as they formed. The oncoids often form around a central nucleus, such as a shell fragment, and a calcium carbonate structure is deposited by encrusting microbes. Oncolites are indicators of warm waters in the photic zone, but are also known in contemporary freshwater environments. These structures rarely exceed 10 cm in diameter. One former classification scheme of cyanobacterial fossils divided them into the
porostromata "Porostromata" is an antiquated form taxon that refers to fossil cyanobacteria. The term porostromate is also used as a descriptor of textures and microstructure of stromatolites and oncolites which contain tubules or other cellular structures ...
and the
spongiostromata "Spongiostromata" is an antiquated form taxon that refers primarily to fossil cyanobacteria. "Spongiostromate" is also used to describe stromatolites and oncolites that do not preserve clear tubules or other cellular microstructure. Pia (1927) ...
. These are now recognized as
form taxa Form classification is the classification of organisms based on their morphology, which does not necessarily reflect their biological relationships. Form classification, generally restricted to palaeontology, reflects uncertainty; the goal of sc ...
and considered taxonomically obsolete; however, some authors have advocated for the terms remaining informally to describe form and structure of bacterial fossils. File:Stromatolites.jpg, Stromatolites left behind by cyanobacteria are the oldest known fossils of life on Earth. This fossil is one billion years old. File:Oncolitic limestone (central Utah, USA) 3.jpg, Oncolitic limestone formed from successive layers of calcium carbonate precipitated by cyanobacteria File:OncolitesAlamoBreccia.jpg, Oncolites from the Late Devonian Alamo bolide impact in Nevada File:Oscillatoriopsis longa fossil.jpg,


Origin of photosynthesis

As far as we can tell,
oxygenic photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
only evolved once (in prokaryotic cyanobacteria), and all photosynthetic eukaryotes (including all plants and algae) have acquired this ability from them. In other words, all the oxygen that makes the atmosphere breathable for
aerobic organism Aerobic means "requiring air," in which "air" usually means oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, ...
s originally comes from cyanobacteria or their later descendants. Cyanobacteria remained principal primary producers throughout the
Proterozoic Eon The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided i ...
(2500–543 Ma), in part because the redox structure of the oceans favored photoautotrophs capable of
nitrogen fixation Nitrogen fixation is a chemical process by which molecular nitrogen (), with a strong triple covalent bond, in the air is converted into ammonia () or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. Atmo ...
. Green algae joined blue-greens as major primary producers on continental shelves near the end of the Proterozoic, but only with the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
(251–65 Ma) radiations of dinoflagellates, coccolithophorids, and diatoms did
primary production In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ...
in marine shelf waters take modern form. Cyanobacteria remain critical to marine ecosystems as primary producers in oceanic gyres, as agents of biological nitrogen fixation, and, in modified form, as the plastids of marine eukaryotic algae.


Origin of chloroplasts

Primary chloroplasts are cell organelles found in some
eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
lineages, where they are specialized in performing photosynthesis. They are considered to have evolved from endosymbiotic cyanobacteria. After some years of debate, it is now generally accepted that the three major groups of primary endosymbiotic eukaryotes (i.e.
green plants Viridiplantae (literally "green plants") are a clade of eukaryotic organisms that comprise approximately 450,000–500,000 species and play important roles in both terrestrial and aquatic ecosystems. They are made up of the green algae, which a ...
, red algae and glaucophytes) form one large monophyletic group called Archaeplastida, which evolved after one unique endosymbiotic event. The morphological similarity between chloroplasts and cyanobacteria was first reported by German botanist Andreas Franz Wilhelm Schimper in the 19th century Chloroplasts are only found in
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...
s and algae, thus paving the way for Russian biologist Konstantin Mereschkowski to suggest in 1905 the symbiogenic origin of the plastid. Lynn Margulis brought this hypothesis back to attention more than 60 years later but the idea did not become fully accepted until supplementary data started to accumulate. The cyanobacterial origin of plastids is now supported by various pieces of
phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...
, genomic, biochemical and structural evidence. The description of another independent and more recent primary endosymbiosis event between a cyanobacterium and a separate eukaryote lineage (the rhizarian '' Paulinella chromatophora'') also gives credibility to the endosymbiotic origin of the plastids. In addition to this primary endosymbiosis, many eukaryotic lineages have been subject to secondary or even tertiary endosymbiotic events, that is the " Matryoshka-like" engulfment by a eukaryote of another plastid-bearing eukaryote. Chloroplasts have many similarities with cyanobacteria, including a circular
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...
, prokaryotic-type ribosomes, and similar proteins in the photosynthetic reaction center. The endosymbiotic theory suggests that photosynthetic bacteria were acquired (by endocytosis) by early
eukaryotic Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
cells to form the first
plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...
cells. Therefore, chloroplasts may be photosynthetic bacteria that adapted to life inside plant cells. Like mitochondria, chloroplasts still possess their own DNA, separate from the nuclear DNA of their plant host cells and the genes in this chloroplast DNA resemble those in cyanobacteria. DNA in chloroplasts codes for
redox Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...
proteins such as photosynthetic reaction centers. The CoRR hypothesis proposes this co-location is required for redox regulation.


Marine origins

Cyanobacteria have fundamentally transformed the geochemistry of the planet. Multiple lines of geochemical evidence support the occurrence of intervals of profound global environmental change at the beginning and end of the Proterozoic (2,500–542 Mya). While it is widely accepted that the presence of molecular oxygen in the early fossil record was the result of cyanobacteria activity, little is known about how cyanobacteria evolution (e.g., habitat preference) may have contributed to changes in biogeochemical cycles through Earth history. Geochemical evidence has indicated that there was a first step-increase in the oxygenation of the Earth's surface, which is known as the Great Oxidation Event (GOE), in the early Paleoproterozoic (2,500–1,600 Mya). A second but much steeper increase in oxygen levels, known as the Neoproterozoic Oxygenation Event (NOE), occurred at around 800 to 500 Mya. Recent chromium isotope data point to low levels of atmospheric oxygen in the Earth's surface during the mid-Proterozoic, which is consistent with the late evolution of marine planktonic cyanobacteria during the Cryogenian; both types of evidence help explain the late emergence and diversification of animals. Understanding the evolution of planktonic cyanobacteria is important because their origin fundamentally transformed the
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
and
carbon cycle The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major compon ...
s towards the end of the
Pre-Cambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...
. It remains unclear, however, what evolutionary events led to the emergence of open-ocean planktonic forms within cyanobacteria and how these events relate to geochemical evidence during the Pre-Cambrian. So far, it seems that ocean geochemistry (e.g.,
euxinic Euxinia or euxinic conditions occur when water is both anoxic and sulfidic. This means that there is no oxygen (O2) and a raised level of free hydrogen sulfide (H2S). Euxinic bodies of water are frequently strongly stratified, have an oxic, highl ...
conditions during the early- to mid-Proterozoic) and nutrient availability likely contributed to the apparent delay in diversification and widespread colonization of open ocean environments by planktonic cyanobacteria during the Neoproterozoic.


Genetics

Cyanobacteria are capable of natural genetic transformation. Natural genetic transformation is the genetic alteration of a cell resulting from the direct uptake and incorporation of exogenous DNA from its surroundings. For bacterial transformation to take place, the recipient bacteria must be in a state of competence, which may occur in nature as a response to conditions such as starvation, high cell density or exposure to DNA damaging agents. In chromosomal transformation, homologous transforming DNA can be integrated into the recipient genome by
homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in cellular organisms but may ...
, and this process appears to be an adaptation for repairing DNA damage.


DNA repair

Cyanobacteria are challenged by environmental stresses and internally generated reactive oxygen species that cause
DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA d ...
. Cyanobacteria possess numerous '' E. coli''-like
DNA repair DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA d ...
gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...
s. Several DNA repair genes are highly conserved in cyanobacteria, even in small
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...
s, suggesting that core DNA repair processes such as recombinational repair, nucleotide excision repair and methyl-directed DNA mismatch repair are common among cyanobacteria.


Classification


Phylogeny


Taxonomy

Historically, bacteria were first classified as plants constituting the class Schizomycetes, which along with the Schizophyceae (blue-green algae/Cyanobacteria) formed the phylum Schizophyta, then in the phylum Monera in the kingdom
Protista A protist () is any eukaryotic organism (that is, an organism whose cells contain a cell nucleus) that is not an animal, plant, or fungus. While it is likely that protists share a common ancestor (the last eukaryotic common ancestor), the e ...
by
Haeckel Ernst Heinrich Philipp August Haeckel (; 16 February 1834 – 9 August 1919) was a German zoologist, naturalist, eugenicist, philosopher, physician, professor, marine biologist and artist. He discovered, described and named thousands of new s ...
in 1866, comprising ''Protogens, Protamaeba, Vampyrella, Protomonae'', and ''Vibrio'', but not ''Nostoc'' and other cyanobacteria, which were classified with algae, later reclassified as the '' Prokaryotes'' by
Chatton Chatton is a village in Northumberland, in England. It is roughly to the east of Wooler. History Chatton has been occupied for many centuries. There has been a church on the site since the twelfth century. There is evidence of occupation i ...
. The cyanobacteria were traditionally classified by morphology into five sections, referred to by the numerals I–V. The first three – Chroococcales, Pleurocapsales, and Oscillatoriales – are not supported by phylogenetic studies. The latter two – Nostocales and Stigonematales – are monophyletic, and make up the heterocystous cyanobacteria. The members of Chroococales are unicellular and usually aggregate in colonies. The classic taxonomic criterion has been the cell morphology and the plane of cell division. In Pleurocapsales, the cells have the ability to form internal spores (baeocytes). The rest of the sections include filamentous species. In Oscillatoriales, the cells are uniseriately arranged and do not form specialized cells (akinetes and heterocysts). In Nostocales and Stigonematales, the cells have the ability to develop heterocysts in certain conditions. Stigonematales, unlike Nostocales, include species with truly branched trichomes. Most taxa included in the phylum or division Cyanobacteria have not yet been validly published under ''The International Code of Nomenclature of Prokaryotes'' (ICNP) except: *The classes Chroobacteria, Hormogoneae, and
Gloeobacteria ''Gloeobacter'' is a genus of cyanobacteria. It is the sister group to all other cyanobacteria. ''Gloeobacter'' is unique among cyanobacteria in not having thylakoids, which are characteristic for all other cyanobacteria and chloroplasts. Inste ...
*The orders Chroococcales, Gloeobacterales, Nostocales, Oscillatoriales, Pleurocapsales, and Stigonematales *The families
Prochloraceae The Prochloraceae are a family of cyanobacteria. References Synechococcales Cyanobacteria families {{cyanobacteria-stub ...
and Prochlorotrichaceae *The genera '' Halospirulina, Planktothricoides, Prochlorococcus, Prochloron'', and '' Prochlorothrix'' The remainder are validly published under the International Code of Nomenclature for algae, fungi, and plants. Formerly, some bacteria, like '' Beggiatoa'', were thought to be colorless Cyanobacteria. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and
National Center for Biotechnology Information The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. Th ...
(NCBI). Class "Cyanobacteriia" * Subclass
Gloeobacteria ''Gloeobacter'' is a genus of cyanobacteria. It is the sister group to all other cyanobacteria. ''Gloeobacter'' is unique among cyanobacteria in not having thylakoids, which are characteristic for all other cyanobacteria and chloroplasts. Inste ...
** Gloeobacterales Cavalier-Smith 2002 * Subclass Phycobacteria ** " Elainellales" ** " Eurycoccales" ** Gloeoemargaritales Moreira et al. 2016 ** " Leptolyngbyales" ** " Neosynechococcales" ** " Phormidesmiales" ** Prochlorococcaceae Komárek & Strunecky 2020 ** Pseudanabaenales Hoffmann, Komárek & Kastovsky 2005 ** Thermostichales Komárek & Strunecký 2020 ** " Thermosynechococcales" ** Nostocophycidae *** Cyanobacteriales Rippka & Cohen-Bazire 1983 ( Chamaesiphonales, Chroococcales, Chroococcidiopsidales, Nostocales, Oscillatoriales, Pleurocapsales, Spirulinales, Stigonematales) ** Synechococcophycidae *** " Limnotrichales" *** Prochlorotrichaceae Burger-Wiersma et al. 1989 *** Synechococcales Hoffmann, Komárek & Kastovsky 2005


Relation to humans


Biotechnology

The unicellular cyanobacterium '' Synechocystis'' sp. PCC6803 was the third prokaryote and first photosynthetic organism whose
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...
was completely sequenced. It continues to be an important model organism. '' Cyanothece'' ATCC 51142 is an important
diazotroph Diazotrophs are bacteria and archaea that fix gaseous nitrogen in the atmosphere into a more usable form such as ammonia. A diazotroph is a microorganism that is able to grow without external sources of fixed nitrogen. Examples of organisms tha ...
ic model organism. The smallest genomes have been found in ''Prochlorococcus'' spp. (1.7 Mb) and the largest in '' Nostoc punctiforme'' (9 Mb). Those of '' Calothrix'' spp. are estimated at 12–15 Mb, as large as
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
. Recent research has suggested the potential application of cyanobacteria to the generation of renewable energy by directly converting sunlight into electricity. Internal photosynthetic pathways can be coupled to chemical mediators that transfer electrons to external electrodes. In the shorter term, efforts are underway to commercialize
algae-based fuels Algae fuel, algal biofuel, or algal oil is an alternative to liquid fossil fuels that uses algae as its source of energy-rich oils. Also, algae fuels are an alternative to commonly known biofuel sources, such as corn and sugarcane. When made fr ...
such as
diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engi ...
,
gasoline Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic c ...
, and
jet fuel Jet fuel or aviation turbine fuel (ATF, also abbreviated avtur) is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is colorless to straw-colored in appearance. The most commonly used fuels for commercial a ...
. Cyanobacteria have been also engineered to produce ethanol and experiments have shown that when one or two CBB genes are being over expressed, the yield can be even higher. Cyanobacteria may possess the ability to produce substances that could one day serve as anti-inflammatory agents and combat bacterial infections in humans. Cyanobacteria's photosynthetic output of sugar and oxygen has been demonstrated to have therapeutic value in rats with heart attacks. While cyanobacteria can naturally produce various secondary metabolites, they can serve as advantageous hosts for plant-derived metabolites production owing to biotechnological advances in systems biology and synthetic biology. Spirulina's extracted blue color is used as a natural food coloring. Researchers from several space agencies argue that cyanobacteria could be used for producing goods for human consumption in future crewed outposts on Mars, by transforming materials available on this planet.


Human nutrition

Some cyanobacteria are sold as food, notably ''
Arthrospira platensis ''Arthrospira platensis'' is a filamentous, gram-negative cyanobacterium. This bacterium is non-nitrogen-fixing photoautotroph. It has been isolated in Chenghai Lake, China, soda lakes of East Africa, and subtropical, alkaline lakes. Morpholo ...
( Spirulina) and others'' ('' Aphanizomenon flos-aquae''). Some microalgae contain substances of high biological value, such as polyunsaturated fatty acids, amino acids, proteins, pigments, antioxidants, vitamins, and minerals. Edible blue-green algae reduce the production of pro-inflammatory cytokines by inhibiting NF-κB pathway in macrophages and splenocytes. Sulfate polysaccharides exhibit immunomodulatory, antitumor, antithrombotic, anticoagulant, anti-mutagenic, anti-inflammatory, antimicrobial, and even antiviral activity against HIV, herpes, and hepatitis.


Health risks

Some cyanobacteria can produce neurotoxins, cytotoxins, endotoxins, and hepatotoxins (e.g., the microcystin-producing bacteria genus microcystis), which are collectively known as cyanotoxins. Specific toxins include anatoxin-a, guanitoxin,
aplysiatoxin Aplysiatoxin is a cyanotoxin produced by certain cyanobacteria species. It is used as a defensive secretion to protect these cyanobacteria from predation by fish, being a potent irritant and carcinogen, by acting as a powerful activator of prote ...
, cyanopeptolin,
cylindrospermopsin Cylindrospermopsin (abbreviated to CYN, or CYL) is a cyanotoxin produced by a variety of freshwater cyanobacteria. CYN is a polycyclic uracil derivative containing guanidino and sulfate groups. It is also zwitterionic, making it highly water ...
, domoic acid, nodularin R (from '' Nodularia''), neosaxitoxin, and
saxitoxin Saxitoxin (STX) is a potent neurotoxin and the best-known paralytic shellfish toxin (PST). Ingestion of saxitoxin by humans, usually by consumption of shellfish contaminated by toxic algal blooms, is responsible for the illness known as paralyti ...
. Cyanobacteria reproduce explosively under certain conditions. This results in algal blooms which can become harmful to other species and pose a danger to humans and animals if the cyanobacteria involved produce toxins. Several cases of human poisoning have been documented, but a lack of knowledge prevents an accurate assessment of the risks, and research by Linda Lawton, FRSE at Robert Gordon University, Aberdeen and collaborators has 30 years of examining the phenomenon and methods of improving water safety. Recent studies suggest that significant exposure to high levels of cyanobacteria producing toxins such as
BMAA β-Methylamino--alanine, or BMAA, is a non-proteinogenic amino acid produced by cyanobacteria. BMAA is a neurotoxin and its potential role in various neurodegenerative disorders is the subject of scientific research. Structure and properties ...
can cause amyotrophic lateral sclerosis (ALS). People living within half a mile of cyanobacterially contaminated lakes have had a 2.3 times greater risk of developing ALS than the rest of the population; people around New Hampshire's Lake Mascoma had an up to 25 times greater risk of ALS than the expected incidence. BMAA from desert crusts found throughout Qatar might have contributed to higher rates of ALS in
Gulf War The Gulf War was a 1990–1991 armed campaign waged by a 35-country military coalition in response to the Iraqi invasion of Kuwait. Spearheaded by the United States, the coalition's efforts against Iraq were carried out in two key phases: ...
veterans.


Chemical control

Several chemicals can eliminate cyanobacterial blooms from smaller water-based systems such as swimming pools. They include
calcium hypochlorite Calcium hypochlorite is an inorganic compound with formula Ca(OCl)2. It is the main active ingredient of commercial products called bleaching powder, chlorine powder, or chlorinated lime, used for water treatment and as a bleaching agent. This ...
, copper sulphate, cupricide, and simazine. The calcium hypochlorite amount needed varies depending on the cyanobacteria bloom, and treatment is needed periodically. According to the Department of Agriculture Australia, a rate of 12 g of 70% material in 1000 L of water is often effective to treat a bloom. Copper sulfate is also used commonly, but no longer recommended by the Australian Department of Agriculture, as it kills livestock, crustaceans, and fish. Cupricide is a chelated copper product that eliminates blooms with lower toxicity risks than copper sulfate. Dosage recommendations vary from 190 mL to 4.8 L per 1000 m2. Ferric alum treatments at the rate of 50 mg/L will reduce algae blooms. Simazine, which is also a herbicide, will continue to kill blooms for several days after an application. Simazine is marketed at different strengths (25, 50, and 90%), the recommended amount needed for one cubic meter of water per product is 25% product 8 mL; 50% product 4 mL; or 90% product 2.2 mL.


Climate change

Climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
is likely to increase the frequency, intensity and duration of cyanobacterial blooms in many eutrophic lakes, reservoirs and estuaries. Bloom-forming cyanobacteria produce a variety of neurotoxins, hepatotoxins and dermatoxins, which can be fatal to birds and mammals (including waterfowl, cattle and dogs) and threaten the use of waters for recreation, drinking water production, agricultural irrigation and fisheries. Toxic cyanobacteria have caused major water quality problems, for example in
Lake Taihu Taihu (), also known as Lake Tai or Lake Taihu, is a lake in the Yangtze Delta and one of the largest freshwater lakes in China. The lake is in Jiangsu province and a significant part of its southern shore forms its border with Zhejiang. With ...
(China),
Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also ha ...
(USA), Lake Okeechobee (USA),
Lake Victoria Lake Victoria is one of the African Great Lakes. With a surface area of approximately , Lake Victoria is Africa's largest lake by area, the world's largest tropical lake, and the world's second-largest fresh water lake by surface area after ...
(Africa) and the
Baltic Sea The Baltic Sea is an arm of the Atlantic Ocean that is enclosed by Denmark, Estonia, Finland, Germany, Latvia, Lithuania, Poland, Russia, Sweden and the North and Central European Plain. The sea stretches from 53°N to 66°N latitude and from ...
. Material was copied from this source, which is available under
Creative Commons Attribution 4.0 International License
Climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
favours cyanobacterial blooms both directly and indirectly. Many bloom-forming cyanobacteria can grow at relatively high temperatures. Increased thermal stratification of lakes and reservoirs enables buoyant cyanobacteria to float upwards and form dense surface blooms, which gives them better access to light and hence a selective advantage over nonbuoyant phytoplankton organisms. Protracted droughts during summer increase water residence times in reservoirs, rivers and estuaries, and these stagnant warm waters can provide ideal conditions for cyanobacterial bloom development. The capacity of the harmful cyanobacterial genus '' Microcystis'' to adapt to elevated CO2 levels was demonstrated in both laboratory and field experiments. ''Microcystis'' spp. take up CO2 and HCO3− and accumulate inorganic carbon in carboxysomes, and strain competitiveness was found to depend on the concentration of inorganic carbon. As a result,
climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
and increased CO2 levels are expected to affect the strain composition of cyanobacterial blooms.


Gallery

File:Lago de coatepeque de color.jpg, Cyanobacteria activity turns
Coatepeque Caldera Caldera De Coatepeque (Nahuatl ''cōātepēc'', "at the snake hill") is a volcanic caldera in El Salvador in Central America. The caldera was formed during a series of rhyolitic explosive eruptions between about 72,000 and 57,000 years ago. ...
lake a turquoise color File:2010 Filamentous Cyanobacteria Bloom near Fiji.jpg, Cyanobacterial bloom near
Fiji Fiji ( , ,; fj, Viti, ; Fiji Hindi: फ़िजी, ''Fijī''), officially the Republic of Fiji, is an island country in Melanesia, part of Oceania in the South Pacific Ocean. It lies about north-northeast of New Zealand. Fiji consis ...
File:Sinilevää Köyliönjärvessä 3.jpg, Cyanobacteria in Lake Köyliö. File:Video- The Cyanobacteria- Oscillatoria and Gleocapsa.webm, Video – '' Oscillatoria'' and ''Gleocapsa'' – with oscillatory movement as filaments of ''Oscillatoria'' orient towards light


See also

* Archean Eon * Bacterial phyla, other major lineages of Bacteria *
Biodiesel Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat ( tallow), soybean oil, or some other vegetable oi ...
* Cyanobiont * Endosymbiotic theory * Geological history of oxygen * Hypolith


Notes


References

;Attribution


Further reading

* * * * * * * *


External links


What are Cyanobacteria and What are its Types?

Webserver for Cyanobacteria Research

Diving an Antarctic Time Capsule Filled With Primordial Life
{{Authority control Phototrophic bacteria Photosynthesis Gram-negative bacteria Environmental chemistry Bacteria phyla