Haloferax Volcanii
   HOME

TheInfoList



OR:

''Haloferax volcanii'' is a
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...
n in the genus '' Haloferax'' in the
Archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...
.


Description and significance

''Haloferax volcanii'' is a
halophilic A halophile (from the Greek word for 'salt-loving') is an extremophile that thrives in high salt concentrations. In chemical terms, halophile refers to a Lewis acidic species that has some ability to extract halides from other chemical species. ...
mesophile A mesophile is an organism that grows best in moderate temperature, neither too hot nor too cold, with an optimum growth range from . The optimum growth temperature for these organisms is 37 °C (about 99 °F). The term is mainly applied ...
archaeon Archaea ( ) is a domain of organisms. Traditionally, Archaea only included its prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even though the domain Archaea cladis ...
that can be isolated from hypersaline environments such as: the
Dead Sea The Dead Sea (; or ; ), also known by #Names, other names, is a landlocked salt lake bordered by Jordan to the east, the Israeli-occupied West Bank to the west and Israel to the southwest. It lies in the endorheic basin of the Jordan Rift Valle ...
, the
Great Salt Lake The Great Salt Lake is the largest saltwater lake in the Western Hemisphere and the eighth-largest terminal lake in the world. It lies in the northern part of the U.S. state of Utah and has a substantial impact upon the local climate, partic ...
, and oceanic environments with high sodium chloride concentrates. ''Haloferax volcanii'' is noteworthy because it can be cultured without much difficulty, rare for an
extremophile An extremophile () is an organism that is able to live (or in some cases thrive) in extreme environments, i.e., environments with conditions approaching or stretching the limits of what known life can adapt to, such as extreme temperature, press ...
. ''H. volcanii'' is chemoorganotrophic, metabolizing sugars as a carbon source. It is primarily aerobic, but is capable of
anaerobic respiration Anaerobic respiration is respiration using electron acceptors other than molecular oxygen (O2). Although oxygen is not the final electron acceptor, the process still uses a respiratory electron transport chain. In aerobic organisms undergoing ...
under
anoxic Anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of dissolved ox ...
conditions. Recently an isolate of this species was studied by researchers at University of California, Berkeley, as part of a project on the survival of
haloarchaea Haloarchaea (halophilic archaea, halophilic archaebacteria, halobacteria) are a class of prokaryotic archaea under the phylum Euryarchaeota, found in water saturated or nearly saturated with salt. 'Halobacteria' are now recognized as archaea r ...
on Mars.


Genome structure

The genome of ''H. volcanii'' consists of a large (4 Mb), multicopy chromosome and several megaplasmids. The complete genome of the wild-type strain of ''H. volcanii'' (DS2) consists of about 4130 genes. The genome has been completely sequenced and a paper discussing it was published in 2010. The molecular biology of ''H. volcanii'' has been extensively studied for the last decade in order to discover more about DNA replication, DNA repair and RNA synthesis. The archaeal proteins used in these processes are extremely similar to Eukaryotic proteins and so are studied primarily as a model system for these organisms. ''H. volcanii'' undergoes prolific
horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). HGT is an important factor in the e ...
through a mechanism of "mating"- cell fusion.


Cell structure and metabolism

Reproduction among ''H. volcanii'' occurs asexually by binary fission. This practice is similar to that of other Archaea and, indeed, that of bacteria. Like many archaea, ''H. volcanii'' cells have no cell wall and therefore are dependent on other mechanisms, such as their
S-layer An S-layer (surface layer) is a part of the cell envelope found in almost all archaea, as well as in many types of bacteria. The S-layers of both archaea and bacteria consists of a Monolayer, monomolecular layer composed of only one (or, in a few c ...
and cytoskeletal proteins, for structure. An individual ''H. volcanii'' archaeon can vary from 1-3 micrometers in diameter. They are pleomorphic, generally transitioning from motile, elongated rod shapes to stationary, biofilm-generating disk shapes as the culture ages. Additionally, biofilms generated by ''H. volcanii'' are capable of rapidly producing honeycomb patterns when exposed to changes in humidity. The membranes of this organism are made of the typical ether linked membrane lipids found solely in archaea and also contain a high level of carotenoids including lycopene, which gives them their distinctive red color. ''Haloferax volcanii'' use a salt in method to maintain osmostasis, rather than the typical compatible solutes method seen in bacteria. This method involves the maintenance of a high degree of potassium ions in the cell to balance the sodium ions outside. For this reason, ''H. volcanii'' has a complex ion regulation system. ''Haloferax volcanii'' will optimally grow between 42 & 45 °C in 1.5–2.5 M NaCl and complex nutrient medium. It will still grow at 37 °C, but still requires the concentrated NaCl and complex medium. Due to the salt in method cytoplasmic proteins are structured to fold in the presence of high ionic concentrations. As such, they typically have a large number of charged residues on the exterior section of the protein and very hydrophobic residues forming a core. This structure considerably increases their stability in saline and even high temperature environments but comes at some loss of processivity compared to bacterial homologs. ''Haloferax volcanii'' respire as their sole source of ATP, unlike several other halobateriacae, such as ''
Halobacterium salinarum ''Halobacterium salinarum'', formerly known as ''Halobacterium cutirubrum'' or ''Halobacterium halobium'', is an extremely halophile, halophilic ocean, marine obligate aerobic archaeon. Despite its name, this is not a bacteria, bacterium, but a mem ...
'' they are incapable of
photophosphorylation In the process of photosynthesis, the phosphorylation of ADP to form ATP using the energy of sunlight is called photophosphorylation. Cyclic photophosphorylation occurs in both aerobic and anaerobic conditions, driven by the main primary source of ...
as they lack the necessary
bacteriorhodopsin Bacteriorhodopsin (Bop) is a protein used by Archaea, most notably by Haloarchaea, a class of the Euryarchaeota. It acts as a proton pump; that is, it captures light energy and uses it to move protons across the membrane out of the cell. The res ...
.


Ecology

Isolates of ''H. volcanii'' are commonly found in high-salinity aquatic environments, such as the Dead Sea. Their precise role in the ecosystem is uncertain, but the carbohydrates contained within these organisms potentially serve many practical purposes. Because of their ability to maintain homeostasis in spite of the salt around them, ''H. volcanii'' could be an important player in advancements in biotechnology. As it is likely that ''H. volcanii'' and comparable species are ranked among the earliest living organisms, they also provide information related to genetics and evolution.


Dead Sea

The
Dead Sea The Dead Sea (; or ; ), also known by #Names, other names, is a landlocked salt lake bordered by Jordan to the east, the Israeli-occupied West Bank to the west and Israel to the southwest. It lies in the endorheic basin of the Jordan Rift Valle ...
contains a very high concentration of sodium, magnesium, and calcium salts. This combination makes the sea an ideal environment for extremophiles such as ''H.volcanii''. The Dead Sea has a diverse community of microorganisms, though the field tests completed by Kaplan and Friedman reported that ''H.volcanii'' had the largest numerical presence within the community. It is common to find higher numbers of the halophile during the summer, as the Dead Sea is much warmer, averaging around 37 degrees Celsius, and thus more conducive to bacterial blooms. Unfortunately, the Dead Sea is becoming less hospitable to extremophiles such as ''H. volcanii'' due to increasing salinity, credited to both natural factors and human activities. As the predominant environment for ''Haloferax volcanii'', the change in salinity places the species at risk.


DNA damage and repair

In prokaryotes the DNA genome is organized in a dynamic structure, the nucleoid, which is embedded in the cytoplasm. Exposure of ''Haloferax volcanii'' to stresses that damage the DNA cause compaction and reorganization of the nucleoid. Compaction depends on the Mre11-Rad50 protein complex that is employed in the homologous recombinational repair of DNA double-strand breaks. Delmas et al. proposed that nucleoid compaction is part of a DNA damage response that accelerates cell recovery by helping DNA repair proteins to locate targets, and by facilitating the search for intact DNA sequences during homologous recombination.


Genetic exchange

It has been shown that ''H. volcanii'', can undergo a process of genetic exchange by mixing cells together on a solid, nitrocellulose membrane. The process of transduction and transformation were ruled out, leaving conjugation as a potential transfer mechanism. This mechanism is thought to be novel from other known forms, as genetic exchange does not seem to be unidirectional like in classic forms of conjugation of other prokaryotic systems. Prolonged contact between cells is required as cells grown in liquid media, while being agitated, show no genetic transfer. Electron microscopy experiments have captured images of ''H. volcanii'' cells attached to each other via multiple cytoplasmic bridge-like structures and it is thought that this is the apparent method of genetic exchange. The protein machinery directly involved in the formation of these bridges and transfer of DNA is yet to be discovered though a study publishing RNAseq data hints at various proteins involved. Others have also shown that manipulating environmental salt concentrations, global glycosylation, and cell surface lipidation alter the rate of the genetic transfer. This archaeal DNA conjugation system has been shown to even work in an interspecies manner as ''H. volcanii'' and the closely related species ''H. mediterranei'' are able to exchange genetic information by this process at a similar level to intraspecies exchange. Unless selecting for the need to recombine the exchanging chromosomes, recombination is not required for survival of the exchanging cells. This can lead to the formation of hybrid cells which contain two distinct chromosomes. CRISPR may also be playing a role in the regulation of this genetic transfer as cells are shown to acquire new spacers into their CRISPR arrays during this process.


Astrobiology

The conditions in which ''Haloferax volcanii'' survives—high salinity and high radiation—are very similar to the conditions found on Mars's surface. Consequently, the organism is currently being used to test the survivability of earth-native extremophiles on Mars. Advances in this field could lead to a greater understanding of the possibility and development of extraterrestrial life.


See also

*
Archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...
*
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 Cell (biology), cellular organi ...
*
Extremophile An extremophile () is an organism that is able to live (or in some cases thrive) in extreme environments, i.e., environments with conditions approaching or stretching the limits of what known life can adapt to, such as extreme temperature, press ...
*
FtsZ FtsZ is a protein encoded by the ''ftsZ'' gene that assembles into a ring at the future site of bacterial cell division (also called the Z ring). FtsZ is a prokaryotic homologue of the eukaryotic protein tubulin. The initials FtsZ mean "Filame ...


References


Sources

* *


Further reading

* * * * * * *


External links


Type strain of ''Haloferax volcanii'' at Bac''Dive'' — the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q16982678 Halobacteria Archaea described in 1975