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.