Electron uptake of sulfate reducing bacteria by using outer-membrane cytochromes
Dept. of Applied Chemistry, The University of Tokyo
Micobially influenced corrosion (MIC) is a serious problem causing enormous economic losses that were estimated to be around 0.3% of the GDP of an industrialized country . MIC is closely related to the metabolic activities of sulfate reducing bacteria (SRB). Desulfovibrio ferrophilus IS5 is a novel SRB strain that was isolated in 2004, and became the first known bacteria that has the ability to extract electrons directly from iron (Fe0) to induce severe iron corrosion under anaerobic conditions . However, the electron uptake process of D. ferrophilus IS5 from the outer solids has not been experimentally proved and the mechanism is poorly understood.To examine if D. ferrophilus IS5 has the outer membrane (OM) electron transfer (ET) pathway, we sequenced its whole genome, and identified several genes that are likely to code for OM c-type cytochromes (c-Cyts). The existence of OM c-Cyts was further evidenced by the spectroscopic and heme-staining analysis for the extracted membrane fractions. Therefore, these results indicate that D. ferrophilus IS5 possesses OM c-Cyts, which potentially facilitate a direct electron flow from extracellular solids to cell interior at the cell/electrode surface. To examine that D. ferrophilus IS5 can extract electrons from electrodes via OM c-Cyts, we performed electrochemical measurements to monitor the microbial electron uptake from an electrode that serves as a sole electron donor. When sulfate was introduced as the metabolic electron acceptor, significant cathodic current increase was observed at an on-set potential of _200 mV (vs. SHE). These results suggest that D. ferrophilus IS5 couples ET via OM c-Cyts with sulfate reduction. Further details for voltammetric data will be discussed.
1）Gerhardus H. Koch et al., Corrosion Cost and Preventive Strategies in the United States, 2002. 2）Hang T. Dinh et al., Nature, 2004, 427, 829.
keywords:Desulfovibrio ferrophilus IS5,Extracellular Electron Transport,Iron Corrosion,Outer membrane Cytochrome c