Hydrogenase- and outer membrane c-type cytochrome-facilitated reduction of technetium(VII) by Shewanella oneidensis MR-1

Authors

Matthew J. Marshall, Pacific Northwest National Laboratory
Andrew Plymale, Pacific Northwest National LaboratoryFollow
David W. Kennedy, Pacific Northwest National LaboratoryFollow
Liang Shi, Pacific Northwest National LaboratoryFollow
Zheming Wang, Pacific Northwest National Laboratory
Samantha B. Reed, Pacific Northwest National Laboratory
Alice Dohnalkova, Pacific Northwest National Laboratory
Cody Simonson, Pacific Northwest National Laboratory
Chongxuan Liu, Pacific Northwest National LaboratoryFollow
Daad A. Saffarini, University of Wisconsin - Milwaukee
Margaret F. Romine, Pacific Northwest National Laboratory
John M. Zachara, Pacific Northwest National LaboratoryFollow
Alexander S. Beliaev, Pacific Northwest National Laboratory
James K. Fredrickson, Pacific Northwest National LaboratoryFollow

Date of this Version

2008

Citation

Environmental Microbiology (2008) 10(1), 125–136; doi:10.1111/j.1462-2920.2007.01438.x

Abstract

Pertechnetate, ⁹⁹Tc(VII)O₄^–, is a highly mobile radionuclide contaminant at US Department of Energy sites that can be enzymatically reduced by a range of anaerobic and facultatively anaerobic microorganisms, including Shewanella oneidensis MR-1, to poorly soluble Tc(IV)O_2(s). In other microorganisms, Tc(VII)O₄^– reduction is generally considered to be catalysed by hydrogenase. Here, we provide evidence that although the NiFe hydrogenase of MR-1 was involved in the H2-driven reduction of Tc(VII)O₄^– [presumably through a direct coupling of H₂ oxidation and Tc(VII) reduction], the deletion of both hydrogenase genes did not completely eliminate the ability of MR-1 to reduce Tc(VII). With lactate as the electron donor, mutants lacking the outer membrane c-type cytochromes MtrC and OmcA or the proteins required for the maturation of c-type cytochromes were defective in reducing Tc(VII) to nanoparticulate TcO₂·nH₂O_(s) relative to MR-1 or a NiFe hydrogenase mutant. In addition, reduced MtrC and OmcA were oxidized by Tc(VII)O₄^–, confirming the capacity for direct electron transfer from these OMCs to TcO₄^–. c-Type cytochrome-catalysed Tc(VII) reduction could be a potentially important mechanism in environments where organic electron donor concentrations are sufficient to allow this reaction to dominate.