Ferroplasma acidarmanus

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A Microbial Biorealm page on the genus Ferroplasma acidarmanus

Classification

Archaea; Euryarchaeota; Thermoplasmata; Thermoplasmatales; Ferroplasmaceae; Ferroplasma; Ferroplasma acidarmanus (7)

Description and significance

Ferroplasma acidarmanus is an aquatic archaeon that is found in streams draining iron mines, most notably Iron Mountain in California. The conditions in these streams are extremely harsh due to high levels of SO4 created as a result of mircobial metabolism, which leads to a pH between 0 and 2.5 (3). F. acidarmanus is one of the few microbes that can survive at such a low pH and can be seen in the stream as streamers of biofilm (5). This microbe has a lot of potential for human use because of its extreme tolerance for low pH. One of the most promising is the application of extracting metal ores, especially iron. However, using the archaeon for this purpose can be difficult because in the process of extracting ore, sulfuric acid is made as a by-product which causes dangerous pollution in water draining from the mine (1). They also could be used for their genes in the creation of acid-stable enzymes for manufacturing industrial catalysts and lubricants (1).

Genome structure

F. acidarmanus has a circular genome on a single chromosome. The strain fer 1 has a draft of its entire genome sequence that is 1,865,438 bases in length (6). Horizontal transfer between other hyperthermophiles is common in extreme environments such as these streams so classifying the different species can be difficult and controversial (8).

Cell structure, metabolism & life cycle

F. acidarmanus is easily recognizable as a member or the order Thermoplasmatales because it does not possess a cell wall or an S-layer as many other archaeon do (8). How they efficiently suvive and carry out cellular processes without a cell wall is poorly understood, but not having a cell wall is thought to have important consequences for surviving in environments with low pH (1). Because of its lack of a cell wall it tends to be amorphous in shape, but is roughly cocci shaped when a shape can be determined (4). This archaeon is a chemolithotroph that derives energy by using Fe3+ dissolved in water to oxidize the sulfur found in iron pyrite ore to sulfuric acid (8). In nature, F. acidarmanus is found on iron pyrite but only sulfur is absolutely necessary for its metabolism because it has been shown to be able to use other metallic sulfur compounds including ZnSO4, MnSO4, and MgSO4 (3). F. acidarmanus is distinguished from other organisms in the genus Ferroplasma because it can live at a greater range of pH’s and it can survive heterotrophically on yeast extract alone, as opposed to others such as F. acidiphilum which cannot survive without metals present (5).

Ecology

F. acidarmanus is found in streams draining iron mines. Here it contributes to an environmental pH between 0 and 2 that very few other organisms can survive in. Within the stream, F. acidarmanus is one of the dominant species, accounting for 85% of the community in these drainage streams (5). It interacts with other acidophiles inhabiting the stream to form biofilms in the shape of slime streamers (5).

Interesting feature

One of the most impressive features of F. acidarmanus is its ability to maintain such an extreme proton gradient with only a cell membrane. Cell membrane impermeability to protons is a key factor in this ability, which is made possible by differences in lipid head groups with tetraether linkages as opposed to ester linkages found in Bacteria and Eukarya (1). Excess protons can be actively transported out of the cell in order to maintain the correct proton gradient (1). This contributes to the Donnan potential which creates a more positive environment on the inside of the cell by storing potassium ions in the cell forcing protons to overcome the charge gradient in order to enter the cell (1). There are other methods for maintaining the proton gradient within other acidophiles such as decreasing the size of membrane channels, but these have yet to be proven to exist in F. acidarmanus, though it is thought to be likely (1). The cytoplasm of the cell is well buffered allowing for pH regulation in slight changes in proton concentrations not accounted for by these mechanisms; chaperone proteins are also able to repair many of the proteins and DNA that may be damaged due to changes in pH within the cell (1).

References

1. Baker-Austin, C. and Dopson, M. “Life in acid: pH homeostasis in acidophiles.” Trends in Microbiology. 2007. Volume 15:4 p. 165-171.

2. Baker-Austin, C, Potrykus, J. Wexler, M. Bond, P. and Dopson, M. “Biofilm development in the extremely acidophilic archaeon ' Ferroplasma acidarmanus' Fer1.” Extremophiles; Nov2010, Vol. 14 Issue 6, p485-491

3. Baumler, D., Jeong, K., Fox, B., Banfield, J., and Kaspar, C. “Sulfate requirement for heterotrophic growth of Ferroplasma acidarmanus strain fer1.” Research in Microbiology. 2005. Volume 156 p.492–498.

4. Edwards, K., Hu, B, Hamers R., Banfield, J. “ A new look at microbial leaching patterns on sulfide minerals.” FEMS Microbiology Ecology. 2001.Volume 34: 3. p. 197-206

5. Edwards KJ, Bond PL, Gihring TM, Banfield JF. 2000. “An Archaeal Iron-Oxidizing Extreme Acidophile Important in Acid Mine Drainage.” Science 287:1796-1799.

6. "Ferroplasma Acidarmanus Fer1." DOE Joint Genome Institute. US Department of Energy. Web. 21 Oct. 2011. <http://img.jgi.doe.gov/cgi-bin/w/main.cgi?section=TaxonDetail>.

7. "Ferroplasma Acidarmanus Fer1." Taxonomy Browser. NCBI. Web. 21 Oct. 2011. <http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info>.

8. Slonczewski, J. and Foster, J. Microbiology An Evolving Science 2nd edition. 2011. W.W. Norton and Company Inc. New York,NY. p. 723-746.