Ferroplasma

''Ferroplasma'' is a genus of Archaea that belong to the family Ferroplasmaceae. Members of the ''Ferroplasma'' are typically acidophillic, pleomorphic, irregularly shaped cocci.

The archaean family Ferroplasmaceae was first described in the early 2000s. To date very few species of ''Ferroplasma'' have been isolated and characterized. Isolated species include ''Ferroplasma acidiphilum'', ''Ferroplasma acidarmanus,'' and ''Ferroplasma thermophilum''. A fourth isolate ''Ferroplasma cupricumulans'' was later determined to belong to a separate genus''.'' All known ''Ferroplasma sp.'' are iron-oxidizers.

Cell characteristics and Physiology

''Ferroplasma'' cells are pleomorphic and lack a cell-wall. All known members of the genera are acidophiles that thrive in environments where pH ranges from 0.0 to 2.0. They are also mesophilic to moderately thermophilic with optimal temperatures ranging from 35-55 °C.

Tetraether-based lipids are an important part of the ''Ferroplasma'' cellular membrane and allow cells to maintain a pH gradient. A study of ''F.'' ''acidarmanus'' found that cytoplasmic pH was maintained ~5.6 while the environmental pH ranged from ~0-1.2. Variations in the tetraether lipids of the family Ferroplasmaceae are used for chemotaxonomic identification at the genus and species level because many members possess identical 16S rRNA sequences.

Members of the genus ''Ferroplasma'' are chemomixotrophs that can oxidize ferrous iron to acquire energy, but despite evidence of carbon fixation, lab cultures often require an organic carbon source such as yeast extract for growth. In the absence of iron, some lab-grown strains have been capable of chemoorganotrophic growth.

Ecological Importance

Iron is the fourth most abundant mineral in earth's crust. As iron-oxidizers ''Ferroplasma sp.'' participate in the biogeochemical of iron. ''Ferroplasma sp.'' are often identified at acid mine drainage (AMD) sites. When ferrous iron (Fe²⁺) is oxidized to ferric iron (Fe³⁺) at mine sites, Fe³⁺ spontaneously reacts with water and iron-sulfur compounds like pyrite to produce sulfate and hydrogen ions. During this reaction ferrous iron, which can be utilized by ''Ferroplasma'', is also regenerated leading to a "propagation cycle" where pH is lowered. The reaction can be described by the following equation:

FeS2 + 14Fe^3+ + 8H2O-> 15Fe^2+ + 2SO4^2- + 16H+

''Ferroplasma'' species are often present at AMD sites where they participate in this cycle through the biotic oxidation of ferrous iron.

''Ferroplasma sp.'' may have important applications for bioleaching metals. Microbial bioleaching occurs naturally in the highly acidic environments that are home to ''Ferroplasma sp.'' Harnessing the power of bioleaching to recover metal from low quality ores and waste material is energetically advantageous compared to smelting and purifying. It also produces fewer toxic byproducts. Studies have shown that the inclusion of ''Ferroplasma thermophilum'' along with the bacteria '' Acidithiobacillus caldus'' and ''Leptospirillum ferriphilum'' can bioaugment the leaching process of chalcopyrite and increase the rate at which copper is recovered.

Isolated Species

''Ferroplasma acidiphilum''

''Ferroplasma acidiphilum'' has been shown to grow as a chemomixotroph and to grow synergistically with the acidophilic bacteria ''Leptospirillum ferriphilum''. The strain ''Ferroplasma acidiphilum'' Y^T is a facultative anaerobe with all the required genes for arginine fermentation. Although it is unclear whether ''Ferroplasma acidiphilum'' Y^T uses its arginine fermentation pathway, the pathway itself is an ancient metabolism that traces back to the last universal common ancestor (LUCA) of the three domains of life.

''Ferroplasma acidarmanus''

''Ferroplasma acidarmanus'' Fer1 was isolated from mine samples collected at Iron Mountain, California. Iron Mountain (CA) is a former mine that is known for its acid mine drainage (AMD) and heavy metal contamination. In addition to being acidophilic, ''F. acidarmanus'' Fer1 is highly resistant to both copper and arsenic.

''Ferroplasma cupricumulans (formerly Ferroplasma cyprexacervatum)''

In 2006 ''Ferroplasma cupricumulans'' was isolated from leachate solution collected from the Myanmar Ivanhoe Copper company (MICCL) mining site in Myanmar. It was noted to be the first slightly thermophilic member of the genus ''Ferroplasma''. However, in 2009 a new genus of acidophilic, thermophilic archaea, ''Acidiplasma'', was identified. It was proposed that, based on 16S rRNA similarity and DNA-DNA hybridization, be transferred to the genus ''Acidiplasma'' and renamed ''Acidiplasma cupricumulans.''

''Ferroplasma thermophilum''

In 2008, Zhou, et al. described the isolation of the organism ''Ferroplasma thermophilum'' L1^T from a chalcopyrite column reactor that was inoculated with acid mine drainage (AMD) from the Daye copper mine in China’s Hubei province. In aerobic conditions with low concentrations of yeast extract ''F. thermophilum'' grows by oxidizing ferrous iron. However, in anaerobic conditions ''F. thermophilum'' reduces ferric iron and sulfate. This makes ''F. thermophilum'' ecologically important for iron and sulfur cycling at pyrite-rich mine sites.

See also

* List of Archaea genera

References

Further reading

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External links

{{Taxonbar, from=Q2666248

Archaea genera
Metallotolerants
Acidophiles
Euryarchaeota