title: Hydrogenase- and outer membrane c-type cytochrome-facilitated reduction of technetium(VII) by Shewanella oneidensis MR-1.
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.
authors: Biological Sciences Division, Pacific Northwest National Laboratory, Richland, WA 99354, USA. matthew.marshall@pnl.gov
authors: Matthew J
authors: MJ
authors: Marshall
authors: Andrew E
authors: AE
authors: Plymale
authors: David W
authors: DW
authors: Kennedy
authors: Liang
authors: L
authors: Shi
authors: Zheming
authors: Z
authors: Wang
authors: Samantha B
authors: SB
authors: Reed
authors: Alice C
authors: AC
authors: Dohnalkova
authors: Cody J
authors: CJ
authors: Simonson
authors: Chongxuan
authors: C
authors: Liu
authors: Daad A
authors: DA
authors: Saffarini
authors: Margaret F
authors: MF
authors: Romine
authors: John M
authors: JM
authors: Zachara
authors: Alexander S
authors: AS
authors: Beliaev
authors: James K
authors: JK
authors: Fredrickson
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D003574:Cytochrome c Group / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004579:Electron Transport; D006859:Hydrogen / Q000378:metabolism; D006864:Hydrogenase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007506:Iron-Sulfur Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D010087:Oxides / Q000737:chemistry / Q000378:metabolism; D020592:Shewanella / Q000737:chemistry / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D013670:Sodium Pertechnetate Tc 99m / Q000737:chemistry / Q000378:metabolism*; D024482:Vitamin K 2 / Q000737:chemistry
chemical_list: D001425:Bacterial Outer Membrane Proteins; D003574:Cytochrome c Group; D007506:Iron-Sulfur Proteins; D010087:Oxides; D024482:Vitamin K 2; D006859:Hydrogen; D013670:Sodium Pertechnetate Tc 99m; C433527:MtrC protein, Shewanella; C118830:iron hydrogenase; C043296:nickel-iron hydrogenase; D006864:Hydrogenase