PNNL

Abstract

Microbial iodate (IO3-) reduction is a major component in the biogeochemical cycling of iodine and the bioremediation of iodine-contaminated environments; however, the molecular mechanism of microbial IO3- reduction is poorly understood. The objective of this study was to determine the protein secretion and metal reduction genes required for IO3- reduction by Shewanella oneidensis with lactate, formate, and 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 GspD was impaired in IO3- reduction. Deletion mutants lacking the cyclic AMP receptor protein CRP, cytochrome maturation permease CcmB, and c-type cytochrome CymA were impaired in IO3- reduction with all electron donors, while c-type cytochrome MtrA and outer membrane b-barrel protein MtrB 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 type II protein secretion of an unidentified IO3- reductase to the S. oneidensis outer membrane.