Reduction of low potential electron acceptors requires the CbcL inner membrane cytochrome of Geobacter sulfurreducens

• Published in: Bioelectrochemistry (Amsterdam, Netherlands) Netherlands), 2016-02, Vol.107 (C), p.7-13
• Main Authors: Zacharoff, Lori, Chan, Chi Ho, Bond, Daniel R.
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; BASIC BIOLOGICAL SCIENCES; Bioelectric Energy Sources; Biofilms - growth & development; Cytochrome; Cytochromes - genetics; Cytochromes - metabolism; Electrochemistry; Electrodes; Electron Transport; Extracellular respiration; Ferric Compounds - metabolism; Gene Deletion; Geobacter; Geobacter - enzymology; Geobacter - metabolism; Manganese Compounds - metabolism; Membrane Proteins - genetics; Membrane Proteins - metabolism; Metal reduction; Microbial electrochemical cell; Oxides - metabolism
• ISSN: 1567-5394; 1878-562X
• DOI: 10.1016/j.bioelechem.2015.08.003

The respiration of metals by the bacterium Geobacter sulfurreducens requires electrons generated by metabolism to pass from the interior of the cell to electron acceptors beyond the cell membranes. The G. sulfurreducens inner membrane multiheme c-type cytochrome ImcH is required for respiration to extracellular electron acceptors with redox potentials greater than −0.1V vs. SHE, but ImcH is not essential for electron transfer to lower potential acceptors. In contrast, deletion of cbcL, encoding an inner membrane protein consisting of b-type and multiheme c-type cytochrome domains, severely affected reduction of low potential electron acceptors such as Fe(III)-oxides and electrodes poised at −0.1V vs. SHE. Catalytic cyclic voltammetry of a ΔcbcL strain growing on poised electrodes revealed a 50mV positive shift in driving force required for electron transfer out of the cell. In non-catalytic conditions, low-potential peaks present in wild type biofilms were absent in ∆cbcL mutants. Expression of cbcL in trans increased growth at low redox potential and restored features to cyclic voltammetry. This evidence supports a model where CbcL is a component of a second electron transfer pathway out of the G. sulfurreducens inner membrane that dominates when redox potential is at or below −0.1V vs. SHE. [Display omitted] •G. sulfurreducens electron transfer pathways vary with redox potential.•CbcL is a putative inner membrane multiheme cytochrome quinone oxioreductase.•Deletion of cbcL impaired reduction of only low potential electron acceptors.•ΔcbcL cyclic voltammetry is specifically altered near −0.15V vs. SHE.•Data is consistent with 3 inner membrane pathways active at different potentials.