The Chroococcales () are an order of

cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

in some classifications which includes the

harmful algal bloom A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, ...

'' Microcystis aeruginosa''. Molecular data indicate that Chroococcales may be

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

, meaning its members may not all belong to the same

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

or have the same common ancestor.

Characteristics

The order is characterized by single, floating cells or colonies which are embedded to a matrix. Also, a lack of differentiation between apical and basal structures exists.

Prochlorales

A heterotypic synonym of Chroococcales is (order) Prochlorales , with type genus "''

Prochloron ''Prochloron'' (from the Greek ''pro'' (before) and the Greek ''chloros'' (green) ) is a genus of unicellular oxygenic photosynthetic prokaryotes commonly found as an extracellular symbiont on coral reefs, particularly in didemnid ascidians (sea ...

''". Additional names of the same nature included: * Division Prochlorophyta Lewin, 1976 * Class Prochlorophyceae Lewin, 1977 * Family Prochloraceae Lewin, 1977 * Chloroxybacteria Margulis & Schwartz, 1982 * Subdivision Prochlorobacteria Jeffrey 1982 * Division Prochlorophycota Shameel 2008 The assignment as a division/subdivision was based on a belief that because this class lack red and blue

phycobilin Phycobilins (from Greek: '' (phykos)'' meaning "alga", and from Latin: ''bilis'' meaning "bile") are light-capturing bilins found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads (though not in green a ...

pigments and have stacked thylakoids, they are so distinct from typical

as to warrant a high rank. The four taxa with "Lewin 1977" became validly published names under the ICNP in 1986, as the revised version , by virtue of being published in '' Int. J. Syst. Bacteriol.'' with a description.

Ecology

They are an important component of

photosynthetic picoplankton Photosynthetic picoplankton or picophytoplankton is the fraction of the photosynthetic phytoplankton of cell sizes between 0.2 and 2 μm (i.e. picoplankton). It is especially important in the central oligotrophic regions of the world ocea ...

. These oligotrophic organisms are abundant in nutrient poor tropical waters and use a unique photosynthetic pigment, divinyl-chlorophyll, to absorb light and acquire energy.

Discovery and naming

This unique group of

phytoplankton Phytoplankton () are the autotrophic (self-feeding) components of the plankton community and a key part of ocean and freshwater Aquatic ecosystem, ecosystems. The name comes from the Greek language, Greek words (), meaning 'plant', and (), mea ...

, with no

pigments, were initially found in 1975 near the

Great Barrier Reef The Great Barrier Reef is the world's largest coral reef system, composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, ...

and off the coast of Mexico (''

''). Prochlorophyta was soon assigned as a new algal sub-class in 1976 by Ralph A. Lewin of the

Scripps Institution of Oceanography Scripps Institution of Oceanography (SIO) is the center for oceanography and Earth science at the University of California, San Diego. Its main campus is located in La Jolla, with additional facilities in Point Loma. Founded in 1903 and incorpo ...

. Other phytoplankton that lacked

pigments were later found in freshwater lakes in the Netherlands by Tineke Burger-Wiersma and colleagues and were termed ''Prochlorothrix'' (additional reading on ''Prochlorothrix'' can be found in a journal article by A.V. Pinevich ). In 1986 ''

Prochlorococcus ''Prochlorococcus'' is a genus of very small (0.6 μm) marine cyanobacteria with an unusual pigmentation ( chlorophyll ''a2'' and ''b2''). These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosyn ...

'' was found by Sallie W. (Penny) Chisholm and colleagues. ''

'' may be responsible for a significant portion of the global primary production.

Morphology

Prochlorophytes are very small microbes generally between 0.2 and 2 μm (

). They morphologically resemble

Cyanobacteria Cyanobacteria ( ) are a group of autotrophic gram-negative bacteria that can obtain biological energy via oxygenic photosynthesis. The name "cyanobacteria" () refers to their bluish green (cyan) color, which forms the basis of cyanobacteri ...

(formerly known as Blue Green Algae). Members of Prochlorophyta have been found as coccoid (spherical) (

Coccus Bacterial cellular morphologies are the shapes that are characteristic of various types of bacteria and often key to their identification. Their direct examination under a light microscope enables the classification of these bacteria (and archaea ...

) shaped, as in ''

'', and as filaments, as in ''Prochlorothrix''.

References

External links

Prochlorophytes
Bacteria orders {{cyanobacteria-stub