Metal Reduction and Protein Secretion Genes Required for Iodate Reduction by Shewanella oneidensis.

The metal-reducing γ-proteobacterium Shewanella oneidensis reduces iodate (IO3- as anaerobic terminal electron acceptor. Microbial IO3- electron transport pathways are postulated to terminate with nitrate (NO3-) reductase, which reduces IO3- as alternative electron acceptor. Recent studies with S. oneidensis, however, have demonstrated that NO3 reductase is not involved in IO3- reduction. The main objective of the present study was to determine the metal reduction and protein secretion genes required for IO3- reduction by Shewanella oneidensis with lactate, formate, or H2 as electron donors. With all electron donors, the type I and type V protein secretion mutants retained wild-type IO3- reduction activity, while the type II protein secretion mutant lacking the outer membrane secretin GspD was impaired in IO3- reduction. Deletion mutants lacking the cyclic AMP receptor protein CRP, cytochrome maturation permease CcmB, and inner membrane-tethered ctype cytochrome CymA were impaired in IO3- reduction with all electron donors, while deletion mutants lacking c-type cytochrome MtrA and outer membrane β-barrel protein MtrB of the outer membrane MtrAB module were were impaired in IO3- reduction with only lactate as electron donor. With all electron donors, mutants lacking the c-type cytochromes OmcA and MtrC of the metal-reducing extracellular electron conduit MtrCAB retained wild-type IO3- reduction activity. These findings indicate that IO3- reduction by S. oneidensis involves electron donor-dependent metal reduction and protein secretion pathway components, including the outer membrane MtrAB module and type II protein secretion of an unidentified IO3- reductase to the S. oneidensis outer membrane. [ABSTRACT FROM AUTHOR]