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  • Title: Hydrogenase- and outer membrane c-type cytochrome-facilitated reduction of technetium(VII) by Shewanella oneidensis MR-1.
    Author: Marshall MJ, Plymale AE, Kennedy DW, Shi L, Wang Z, Reed SB, Dohnalkova AC, Simonson CJ, Liu C, Saffarini DA, Romine MF, Zachara JM, Beliaev AS, Fredrickson JK.
    Journal: Environ Microbiol; 2008 Jan; 10(1):125-36. PubMed ID: 17888007.
    Abstract:
    Pertechnetate, (99)Tc(VII)O(4)(-), 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)O(4)(-) 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 H(2)-driven reduction of Tc(VII)O(4)(-)[presumably through a direct coupling of H(2) 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 TcO(2) x nH(2)O((s)) relative to MR-1 or a NiFe hydrogenase mutant. In addition, reduced MtrC and OmcA were oxidized by Tc(VII)O(4)(-), confirming the capacity for direct electron transfer from these OMCs to TcO(4)(-). 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.
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