Extracellular Electron Exchange Capabilities ofDesulfovibrio ferrophilusandDesulfopila corrodens

Microbial extracellular electron transfer plays an important role in diverse biogeochemical cycles, metal corrosion, bioelectrochemical technologies, and anaerobic digestion. Evaluation of electron uptake from pure Fe(0) and stainless steel indicated that, in contrast to previous speculation in the literature,Desulfovibrio ferrophilusandDesulfopila corrodensare not able to directly extract electrons from solid-phase electron-donating surfaces.D. ferrophilusgrew with Fe(III) as the electron acceptor, butDp. corrodensdid not.D. ferrophilusreduced Fe(III) oxide occluded within porous alginate beads, suggesting that it released a soluble electron shuttle to promote Fe(III) oxide reduction. Conductive atomic force microscopy revealed that theD. ferrophiluspili are electrically conductive and the expression of a gene encoding an aromatics-rich putative pilin was upregulated during growth on Fe(III) oxide. The expression of genes for multi-hemec-type cytochromes was not upregulated during growth with Fe(III) as the electron acceptor, and genes for a porin-cytochrome conduit across the outer membrane were not apparent in the genome. The results suggest thatD. ferrophilushas adopted a novel combination of strategies to enable extracellular electron transport, which may be of biogeochemical and technological significance.