Extracellular Reduction of Hexavalent Chromium by Cytochromes MtrC and OmcA of Shewanella oneidensis MR-1

Purification and Characterization of the [NiFe]-Hydrogenase of Shewanella oneidensis MR-1

“…Future research will focus on testing these hypotheses. Because they are found in the MR-1 periplasm, Tc(IV)O 2 ⅐ nH 2 Ϫ , H 2 molecules diffuse into the NiFe active center that is buried deeply inside the hydrogenase (blue circle, large subunit; green circle, small subunit) via a H 2 channel. After oxidation, the released protons are transported out of the hydrogenase through a proposed proton channel into the PS, where they can be transported into the cytoplasm through H ϩ transporters (orange circle) located in the cytoplasmic or inner membrane (IM).…”

“…Phenotypic analyses of MR-1 mutants reveal that while multiheme c-type cytochromes, such as MtrC and OmcA, are directly involved in reduction of Fe(III) oxides, Tc(VII), U(VI), and Cr(VI), [NiFe]-hydrogenase ([NiFe]-H 2 ase) has also been implicated in Tc(VII) reduction (2,3,6,23,24,31). Biochemical characterization of purified proteins demonstrated that MtrC and/or OmcA could bind to the surface of crystalline Fe(III) oxide hematite (␣-Fe 2 O 3 ) and reduce hematite as well as Tc(VII), U(VI), Cr(VI), and chelated Fe(III), providing direct evidence that MtrC and OmcA can serve as terminal reductases for extracellular reduction of these oxidized metals and metal contaminants (2,10,13,17,19,25,35,36,40,42). MR-1 [NiFe]-H 2 ase is believed to be localized in the periplasm, where it has been implicated in both H 2 formation and oxidation in addition to Tc(VII) reduction (24,26).…”

Disruption of Putrescine Biosynthesis in Shewanella oneidensis Enhances Biofilm Cohesiveness and Performance in Cr(VI) Immobilization

“…S5 in the supplemental material). As it has been reported that, under similar conditions, S. oneidensis MR-1 reduces dichromate to Cr(III) (19,46), we obtained the XANES spectra of Cr in the biofilms of both WT and CP2-1-S1 to examine the Cr oxidation states (Fig. 3).…”

“…Biofilms of S. oneidensis play an important role in many environmental and biotechnological processes, including removing toxic metal contaminants, such as uranium and chromium, from the aqueous phase by transforming them into less soluble species (17,(19)(20)(21). Previous studies have suggested that exposure to toxic contaminants, e.g., chromate, could cause dispersal of S. oneidensis biofilms (14).…”

Extracellular Electron Transfer in in situ Petroleum Hydrocarbon Bioremediation

“…Similarly, Shewanella has been observed to precipitate reduced chrome (Cr(III)), likely involving the same enzymes as for Fe(III) reduction (Belchik et al, 2011). It can be hypothesised that the expression of extracellular electron transport pathways for soluble, oxidized electron acceptors precipitating during reduction, such as chrome and uranium was intended to keep the precipitates from forming inside the cells.…”