Thermophilic iron -reducer

Zhang C, Liu S, Phelps TJ, Cole DR, Horita J, Fortier SM, Elless M, Valley JW (1997) Physiochemical, mineralogical, and isotopic characterization of magnetite-rich iron oxides formed by thermophilic iron-reducing bacteria. Geochim Cosmochim Acta 61 4621-4632... 

Greene AC, Patel BKC, Sheehy A. 1997. Deferribacter thermophilus gen. nov., sp. nov., a novel thermophilic manganese- and iron-reducing bacterium isolated from a petroleum reservoir. Int J Syst Bacteriol 47 505-9. 

This key enzyme of the dissimilatory sulfate reduction was isolated from all Desulfovibrio strains studied until now 135), and from some sulfur oxidizing bacteria and thermophilic Archaea 136, 137). The enzymes isolated from sulfate-reducing bacteria contain two [4Fe-4S] clusters and a flavin group (FAD) as demonstrated by visible, EPR, and Mossbauer spectroscopies. With a total molecular mass ranging from 150 to 220 kDa, APS reductases have a subunit composition of the type 012)32 or 02)3. The subunit molecular mass is approximately 70 and 20 kDa for the a and )3 subunits, respectively. Amino-acid sequence data suggest that both iron-sulfur clusters are located in the (3 subunit... 

Although under chemolithoautotrophic growth conditions, cell densities of only 3-5 x 10 cells per milliliter were observed, the specific rate of Fe(III) reduced per cell unit was about 10 times faster than what had been published for any other Fe(lll) reducer. This strengthens the hypothesis that microbially mediated Fe(III) reduction by obligately anaerobic thermophiles could have been an important process on early Earth, when elevated temperatures were predominant (Baross 1998 Kashefi and Lovley 2000), which includes the involvement in the formation of specific Banded Iron Formations. In light of the properties of the above Fe(lll) reducers, the theories on the origin and biogeochemistry of Banded Iron Formations should be revisited. 

Thermophilic microbes have been known for some years from the hot springs of Yellowstone National Park, USA (Farmer, 2000) but now are also documented from deep ocean hydrothermal vents, the most extreme of which is an Fe(III)-reducing member of the Archaea that can grow at 121°C (Kashefi St Lovley, 2003). Ocean vent microbial communities are diverse and include Archaea and Bacteria (Hoelc et al., 2003) which utilize hydrogen- and iron-oxidizing and sulfur-reducing metabolisms to produce microbial mats. They form rod-like, coccoid, and filamentous forms (Reysenbach and Cady, 2001). An equally diverse array of thermophilic microbes is also... 

David Boone, a Portland State Univrsity microbial ecologist, studies include the microbiology of deep terrestrial subsurfaces. He discovered an iron and sulfate-reducing bacterium, Bacillus infernos, the first anaerobic member of the bacterial genus Bacillus. The Bacillus from hell , as the name implies, was isolated 2700 m below the land surface. It is thermophilic (60°C), halotolerant (salt concentrations 0.6 M) and slightly alkaliphilic [24]. 

SRBs reduce sulfate to sulfide, which usually shows up as hydrogen sulfide or, if iron is available, as black ferrous sulfide (Fig. 10.10). In the absence of sulfate, some strains can function as fermenters and use organic compounds such as pyruvate to produce acetate, hydrogen, and carbon dioxide. Many SRB strains also contain hydrogenase enzymes, which allow them to consume hydrogen. Most common strains of SRB grow best at temperatures from 25 to 35°C. A few thermophilic strains capable of functioning efficiently at more than 60°C have been reported. 

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