Sulfur-mediated electron shuttling during bacterial iron reduction

Science  30 May 2014:
Vol. 344, Issue 6187, pp. 1039-1042
DOI: 10.1126/science.1252066

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How bacteria manage to breathe on rust

In the absence of oxygen, anaerobic bacteria turn to other chemical compounds during respiration. This can be helpful in detoxifying heavy-metal pollution. Flynn et al. (see the Perspective by Friedrich and Finster) found that alkaline conditions prevent a detoxifying bug—Shewanella oneidensis—from using enzymes to reduce rust-like minerals. Instead, the bacteria reduce elemental sulfur compounds, generating hydrogen sulfide that reduces the iron indirectly. This interplay between anoxic biogeochemical cycles may explain why some anaerobic bacteria contain the genetic machinery necessary to reduce multiple compounds besides oxygen.

Science, this issue p. 1039; see also p. 974


Microbial reduction of ferric iron [Fe(III)] is an important biogeochemical process in anoxic aquifers. Depending on groundwater pH, dissimilatory metal-reducing bacteria can also respire alternative electron acceptors to survive, including elemental sulfur (S0). To understand the interplay of Fe/S cycling under alkaline conditions, we combined thermodynamic geochemical modeling with bioreactor experiments using Shewanella oneidensis MR-1. Under these conditions, S. oneidensis can enzymatically reduce S0 but not goethite (α-FeOOH). The HS produced subsequently reduces goethite abiotically. Because of the prevalence of alkaline conditions in many aquifers, Fe(III) reduction may thus proceed via S0-mediated electron-shuttling pathways.

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