Ferroplasma

NCBI: Taxonomy Genome

Ferroplasma acidophilum; cells are pleomorphic. Image courtesy of Pivovarova et al. (2002).

Classification

Higher order taxa:

Archaea; Euryarchaeota; Thermoplasmata; Thermoplasmatales; Ferroplasmaceae

Species:

Ferroplasma acidiphilum YT, F. acidarmanus

Description and Significance

Ferroplasma spp. are acidophilic microorganisms that help accelerate the rate of disintegration of metal sulfide minerals . The oxidative disintegration of Sulfides (primarily pyrite, FeS₂) plays an important role in the geochemical sulfur cycle and causes the formation of acid mine drainage (AMD). Ferroplasma helps precipitate the rate of pyrite through regeneration of Fe³⁺, the primary pyrite oxidant at low pH.

Genome Structure

No Ferroplasma spp. has been sequenced yet (F. acidarmanus sequencing is in progress), although certain genes have been investigated such as the genes responsible for arsenic resistance in F. acidarmanus. Gihring et al. (2003) discovered that some of the known arsenic resistance genes were not present in F. acidarmanus, indicating the presence of other unknown arsenic-resistance genes.

Cell Structure and Metabolism

F. acidiphilum cells during exponential phase are pleomorphic in shape and are 0.4-0.9 um in length. They also have membrane bound electron-transport zones and no cell wall.

Sulfides exposed to air and water undergo oxidative dissolution by the reaction FeS₂ + 14Fe³⁺ + 8H₂O --> 15Fe²⁺ +2SO₄^2- + 16H⁺. By producing Fe³⁺, Ferroplasma is able to drive this reaction forward, oxidizing FeS₂.

Both Ferroplasma species are heterotrophic, growing best on yeast extract. These species are also aerobic, requiring oxygen for growth.

Ecology

Stream at B-drift in Iron Mountain (~1m across). The biofilm is contains pyritic sediments and forms dense slime streamers during summer and fall months here. Image courtesy of Edwards et al.

An Iron Mountain Stream, courtesy of Woods Hole Currents.

Ferroplasma has been located at Iron Mountain in northern California. It can grow where the temperature is between 15 and 47^oC, with an optimum temperature of 35-36^oC, and where the pH is between 1.3 and 2.2, with an optimum pH of 1.7.

References

Pivovarova et al. 2002. Phenotypic Features of Ferroplasma acidiphilum Strains Y^T and Y-2. Microbiology Vol. 71 No. 6: 698-706.

Edwards et al. 2000. An Archaeal Iron-Oxidizing Extreme Acidophile Important in Acid Mine Drainage. Science Vol 287: 1796-1799.

Gihring et al. 2003. Arsenic resistance in the archaeon "Ferroplasma acidarmanus": new insights into the structure and evolution of the ars genes. Extremophiles Vol. 7 Iss. 2: 123-130.