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Fe(III) reduction during pyruvate fermentation by D esulfotomaculum reducens strain MI ‐1

Desulfotomaculum reducens MI ‐1 is a G ram‐positive, sulfate‐reducing bacterium also capable of reducing several metals, among which is F e(III). Very limited knowledge is available on the potential mechanism(s) of metal reduction among Gram‐positive bacteria, despite their preponderance in the micr...

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Bibliographic Details
Published in:Geobiology 2014-01, Vol.12 (1), p.48-61
Main Authors: Dalla Vecchia, E., Suvorova, E. I., Maillard, J., Bernier‐Latmani, R.
Format: Article
Language:English
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Summary:Desulfotomaculum reducens MI ‐1 is a G ram‐positive, sulfate‐reducing bacterium also capable of reducing several metals, among which is F e(III). Very limited knowledge is available on the potential mechanism(s) of metal reduction among Gram‐positive bacteria, despite their preponderance in the microbial communities that inhabit some inhospitable environments (e.g., thermal or hyperthermal ecosystems, extreme p H or salinity environments, heavy metal or radionuclide contaminated sediments). Here, we show that in the presence of pyruvate, this micro‐organism is capable of reducing both soluble F e(III)‐citrate and solid‐phase hydrous ferric oxide, although growth is sustained by pyruvate fermentation rather than F e(III) respiration. Despite the fact that Fe(III) reduction does not support direct energy conservation, D . reducens uses it as a complementary means of discarding excess reducing equivalent after H 2 accumulation in the culture headspace renders proton reduction unfavorable. Thus, F e(III) reduction permits the oxidation of greater amounts of pyruvate than fermentation alone. F e(III) reduction by D . reducens is mediated by a soluble electron carrier, most likely riboflavin. Additionally, an intracellular electron storage molecule acts as a capacitor and accumulates electrons during pyruvate oxidation for slow release to F e(III). The reductase responsible for the transfer of electrons from the capacitor to the soluble carrier has not been identified, but data presented here argue against the involvement of c ‐type cytochromes.
ISSN:1472-4677
1472-4669
DOI:10.1111/gbi.12067