Q-292. Roles of OmcB and OmcE from Shewanella putrefaciens W3-18-1 in Iron (III) and Manganese (IV) Reduction

J. Chen1, H. Gao1,2, Y. Liang1,3, Z. He1, J. Zhou1;
1Univ. of Oklahoma, Norman, OK, 2Michigan State Univ., East Lansing, MI, 3Central South Univ., Changsha, CHINA.

Shewanella putrefaciens W3-18-1 differs from S. oneidensis MR-1 in the metal reduction gene cluster significantly. According to genome annotation, an analog to OmcB of MR-1 is present while analogs to OmcA or to the secondary metal reductase and accessory proteins (MtrDEF) of MR-1 lack. Instead, it possesses an 11-heme c-type cytochrome OmcE at the location of OmcA in MR-1. To examine whether OmcE of W3-18-1 is functionally equivalent to OmcA of MR-1 and whether OmcB/A is the only iron reductase in W-18-1, mutational analyses were carried out. In-frame omcB, omcE single and omcBE double deletion strains were constructed and confirmed by sequencing. As expected, mutations in these genes barely affected aerobic growth of these mutants. Tests under anaerobic conditions with 50 mM lactate as electron donors and one of Fe2O3, α-FeO(OH), β-FeO(OH), ferric citrate and MnO2 as electron acceptors showed that reduction of solid-phase Fe(III) and Mn(IV) in S. putrefaciens W3-18-1 was dependent on the presence of at least one OMC protein (OmcE, OmcB) and deletion of both OMCs (OmcE & OmcB) leads to severe deficiency in reduction of solid-phase Fe(III) and MnO2 as observed in MR-1. This result suggests that OmcE of W3-18-1 is functionally equivalent to OmcA of MR-1 in insoluble metal reduction. Interestingly, the double mutant of W3-18-1 showed deficiency in soluble iron reduction much more severe than that of MR-1. Whether this difference is due to MtrDEF are currently under investigation.