title: Analyses of current-generating mechanisms of Shewanella loihica PV-4 and Shewanella oneidensis MR-1 in microbial fuel cells.
abstract: Although members of the genus Shewanella have common features (e.g., the presence of decaheme c-type cytochromes [c-cyts]), they are widely variable in genetic and physiological features. The present study compared the current-generating ability of S. loihica PV-4 in microbial fuel cells (MFCs) with that of well-characterized S. oneidensis MR-1 and examined the roles of c-cyts in extracellular electron transfer. We found that strains PV-4 and MR-1 exhibited notable differences in current-generating mechanisms. While the MR-1 MFCs maintained a constant current density over time, the PV-4 MFCs continued to increase in current density and finally surpassed the MR-1 MFCs. Coulombic efficiencies reached 26% in the PV-4 MFC but 16% in the MR-1 MFCs. Although both organisms produced quinone-like compounds, anode exchange experiments showed that anode-attached cells of PV-4 produced sevenfold more current than planktonic cells in the same chamber, while planktonic cells of MR-1 produced twice the current of the anode-attached cells. Examination of the genome sequence indicated that PV-4 has more c-cyt genes in the metal reductase-containing locus than MR-1. Mutational analysis revealed that PV-4 relied predominantly on a homologue of the decaheme c-cyt MtrC in MR-1 for current generation, even though it also possesses two homologues of the decaheme c-cyt OmcA in MR-1. These results suggest that current generation in a PV-4 MFC is in large part accomplished by anode-attached cells, in which the MtrC homologue constitutes the main path of electrons toward the anode.
authors.affiliation: 305 Komaba Open Laboratory, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan. Phone: 81 3 5452 5749. Fax: 81 3 5452 5749. E-mail for Kazuhito Hashimoto: hashimoto@light.t.u-tokyo.ac.jp E-mail for Kazuya Watanabe: watanabe@light.t.u-tokyo.ac.jp.
authors.forename: Gregory J
authors.initials: GJ
authors.lastname: Newton
authors.forename: Shigeki
authors.initials: S
authors.lastname: Mori
authors.forename: Ryuhei
authors.initials: R
authors.lastname: Nakamura
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Hashimoto
authors.forename: Kazuya
authors.initials: K
authors.lastname: Watanabe
mesh_terms: D001674:Bioelectric Energy Sources; D003574:Cytochrome c Group / Q000235:genetics / Q000378:metabolism; D004560:Electricity; D004579:Electron Transport / Q000235:genetics; D010084:Oxidation-Reduction; D020592:Shewanella / Q000145:classification / Q000235:genetics / Q000502:physiology*
chemical_list: D003574:Cytochrome c Group