Haloarchaea

Source: Wikipedia, the free encyclopedia.
"Halobacteria" redirects here. For the genus, see Halobacterium.

Haloarchaea
µm
in length.
Scientific classification
Domain:
Archaea
Kingdom:
Euryarchaeota
Phylum:
Euryarchaeota
Class:
Halobacteria

Grant et al. 2002
Order
Synonyms
  • Halomebacteria Cavalier-Smith 2002
  • Haloarchaea DasSarma and DasSarma 2008

Haloarchaea (halophilic archaea, halophilic archaebacteria, halobacteria)

prokaryotic organisms under the archaeal phylum Euryarchaeota,[2] found in water saturated or nearly saturated with salt. Halobacteria are now recognized as archaea rather than bacteria and are one of the largest groups. The name 'halobacteria' was assigned to this group of organisms before the existence of the domain Archaea was realized, and while valid according to taxonomic rules, should be updated.[3]
Halophilic archaea are generally referred to as haloarchaea to distinguish them from halophilic bacteria.

These

NaCl for growth and survival.[4] They are a distinct evolutionary branch of the Archaea distinguished by the possession of ether-linked lipids and the absence of murein in their cell walls
.

Haloarchaea can grow aerobically or anaerobically. Parts of the membranes of haloarchaea are purplish in color,[5] and large blooms of haloarchaea appear reddish, from the pigment bacteriorhodopsin, related to the retinal pigment rhodopsin, which it uses to transform light energy into chemical energy by a process unrelated to chlorophyll-based photosynthesis.

Haloarchaea have a potential to solubilize phosphorus. Phosphorus-solubilizing halophilic archaea may well play a role in P (phosphorus) nutrition to vegetation growing in hypersaline soils. Haloarchaea may also have applications as inoculants for crops growing in hypersaline regions.[6]

Taxonomy

The extremely halophilic, aerobic members of Archaea are classified within the family Halobacteriaceae, order Halobacteriales in Class III. Halobacteria of the phylum Euryarchaeota (International Committee on Systematics of Prokaryotes, Subcommittee on the taxonomy of Halobacteriaceae). As of May 2016, the family Halobacteriaceae comprises 213 species in 50 genera.

Gupta et al.[7][8] divides the class of Halobacteria in three orders.

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN)[9] and National Center for Biotechnology Information (NCBI).[2]

16S rRNA based
LTP_06_2022[10][11][12]
 53 marker proteins based GTDB 08-RS214[13][14][15]

Halobacteriaceae 2 *

Halobacteriaceae *

"Haladaptaceae" *

Halostella {QS-9-68-17} *

Halalkalicoccus {"Halalkalicoccaceae"} *

Halococcus {Halococcaceae}

Halobacteriaceae 4 *

Natronoarchaeum
{"Natronoarchaeaceae"} *

Salinarchaeum {"Salinarchaeaceae"}

Natrialbaceae

Salinirubrum
*

Haloferacaceae (incl. Halorubraceae)

Halobacteriales

Salinarchaeum {"Salinarchaeaceae"}

Halostella {QS-9-68-17} *

Natronoarchaeum
{"Natronoarchaeaceae"} *

Natrialbaceae

Note: * paraphyletic Halobacteriaceae

Molecular signatures

Detailed phylogenetic and comparative analyses of genome sequences from members of the class Haloarchaea has led to division of this class into three orders,

phosphopyruvate hydratase, RNA-associated protein, threonine synthase, aspartate aminotransferase, precorrin-8x methylmutase, protoporphyrin IX magnesium chelatase and geranylgeranylglyceryl phosphate synthase-like protein.[7]

Living environment

Salt ponds with pink colored Haloarchaea on the edge of San Francisco Bay, near Fremont, California

Haloarchaea require salt concentrations in excess of 2 mol/L (or about 10%, three times the

ocean salinity which is around 35g/L salt – 3.5%) in the water to grow, and optimal growth usually occurs at much higher concentrations, typically 20–30% (3.4 - 5.2 mol/L of NaCl). [16] However, Haloarchaea can grow up to saturation (about 37% salts).[17] Optimal growth also occurs when pH is neutral or basic and temperatures at 45°C. Some haloarchaea though can grow even when temperatures exceed 50°C. [16]

Haloarchaea are found mainly in hypersaline lakes and solar salterns. Their high densities in the water often lead to pink or red colourations of the water (the cells possessing high levels of carotenoid pigments, presumably for UV protection).[18] The pigmentation will become enhanced when oxygen levels are low due to an increase in a red pigmented ATP. [16] Some of them live in underground rock salt deposits, including one from middle-late Eocene (38-41 million years ago).[19] Some even older ones from more than 250 million years ago have been reported.[20] Haloarchaea is also used to treat water that is high in salinity. This is due to its ability to withstand high nutrient levels and the heavy metals that may be present. [16]

Adaptations to environment

Haloarchaea can grow at an aw close to 0.75, yet a

compatible solutes such as potassium chloride (KCl) in their intracellular space to allow them to balance osmotic pressure.[23] Retaining these salts is referred to as the “salt-in” method where the cell accumulates a high internal concentration of potassium.[24] Because of the elevated potassium levels, haloarchaea have specialized proteins that have a highly negative surface charge to tolerate high potassium concentrations.[25]

Haloarchaea have adapted to use glycerol as a carbon and energy source in catabolic processes, which is often present in high salt environments due to Dunaliella species that produce glycerol in large quantities.[24]

Phototrophy

fixing carbon from carbon dioxide.[26] Early evolution of retinal proteins has been proposed as the purple Earth hypothesis.[5]

Cellular shapes

Haloarchaea are often considered pleomorphic, or able to take on a range of shapes—even within a single species. This makes identification by microscopic means difficult, and it is now more common to use gene sequencing techniques for identification instead.

One of the more unusually shaped Haloarchaea is the "

osmolarity
of the water, permitting cell shapes that would be difficult, if not impossible, under other conditions.

As exophiles

Haloarchaea have been proposed as a kind of life that could

live on Mars; since the Martian atmosphere has a pressure below the triple point of water, freshwater species would have no habitat on the Martian surface. The presence of high salt concentrations in water lowers its freezing point, in theory allowing for halophiles to exist in saltwater on Mars.[27] Recently, haloarchaea was sent 36 km (about 22 miles) up into Earths atmosphere, within a balloon. The two types that were sent up were able to survive the freezing temperatures and high radiation levels. [28]
This only further extends the theory that halophiles could exist on Mars.

Medical use

Certain types of haloarchaea have been found to produce carotenoids, which normally has to be synthesized using chemicals. With haloarchaea naturally producing it, there is now a natural way to synthesize carotenoids for medical use. [29] Haloarchaea has also been proposed to help meet the high demand of carotenoids by pharmaceutical companies due to how easy it can be grown in a lab.[30] Genes in Haloarchaea can also be manipulated in order to produce various strands of carotenoids, further helping meet pharmaceutical companies needs.[29]

Haloarchaea is also present within the human gut, mostly predominant in the gut of people who live in Korea. Haloarchaea are most abundant in Koreans guts rather than methanogens due to their saltier diets. This also shows that the archaeome in the human gut can vary drastically depending on region and what is eaten.[31]

Climate change

Haloarchaea have been proposed that certain types can be used to make biodegradable plastics, which could help decrease plastic pollution. Haloarchaea are able to produce polyhydroxyalkanote (PHA), polyhydroxybutyrate (PHB) and polyhydroxyvalerate (PHV), when exposed to certain conditions. For large scale production of these bioplastics, haloarchaea is favored due to the low cost, fast growth, and lack of need to sterilize area due to the salty environment they prefer. They are also a cleaner option for bioplastics due to them not needing chemicals for cell lysis and have a higher recyclability of the process. [32]

Certain types of haloarchaea have also been found to poses denitrifying characteristics. If haloarchaea are complete denitrifies, they could aid salt marsh and other salty environments by buffering these areas of nitrate and nitrite. This could help animal diversity and decrease pollution with in these waterways. However, when tested in the lab, haloarchaea have been found to be partial denitrifies. This means that if haloarchaea are used to treat areas that are high in nitrite and nitrate, they could contribute to nitrogen contaminates and cause an increase in ozone depletion, furthering climate change.[33] The only type of haloarchaea that has been found to reduce nitrogen pollution to atmospheric nitrogen has been Haloferax mediterranei. [34] This shows that haloarchaea may be contributing to nitrogen pollution and isn't a suitable solution to reducing nitrate and nitrite within high salinity areas.   

See also

References

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  2. ^ a b Sayers; et al. "Halobacteria". National Center for Biotechnology Information (NCBI) taxonomy database. Retrieved 2022-06-05.
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  9. ^ J.P. Euzéby. "Halobacteria". List of Prokaryotic names with Standing in Nomenclature (LPSN). Retrieved 2021-11-17.
  10. ^ "The LTP". Retrieved 10 May 2023.
  11. ^ "LTP_all tree in newick format". Retrieved 10 May 2023.
  12. ^ "LTP_06_2022 Release Notes" (PDF). Retrieved 10 May 2023.
  13. ^ "GTDB release 08-RS214". Genome Taxonomy Database. Retrieved 10 May 2023.
  14. ^ "ar53_r214.sp_label". Genome Taxonomy Database. Retrieved 10 May 2023.
  15. ^ "Taxon History". Genome Taxonomy Database. Retrieved 10 May 2023.
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  27. ^ DasSarma S (2006). "Extreme halophiles are models for astrobiology" (PDF). Microbe-American Society for Microbiology. 1 (3): 120. Archived from the original (PDF) on 2007-02-02.
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Further reading

Journals

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External links
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