Shewanella oneidensis MR-1 restores menaquinone synthesis to a menaquinone-negative mutant.
The mechanisms underlying the use of insoluble electron acceptors by metal-reducing bacteria, such as Shewanella oneidensis MR-1, are currently under intensive study. Current models for shuttling electrons across the outer membrane (OM) of MR-1 include roles for OM cytochromes and the possible excretion of a redox shuttle. While MR-1 is able to release a substance that restores the ability of a menaquinone (MK)-negative mutant, CMA-1, to reduce the humic acid analog anthraquinone-2,6-disulfonate (AQDS), cross-feeding experiments conducted here showed that the substance released by MR-1 restores the growth of CMA-1 on several soluble electron acceptors. Various strains derived from MR-1 also release this substance; these include mutants lacking the OM cytochromes OmcA and OmcB and the OM protein MtrB. Even though strains lacking OmcB and MtrB cannot reduce Fe(III) or AQDS, they still release a substance that restores the ability of CMA-1 to use MK-dependent electron acceptors, including AQDS and Fe(III). Quinone analysis showed that this released substance restores MK synthesis in CMA-1. This ability to restore MK synthesis in CMA-1 explains the cross-feeding results and challenges the previous hypothesis that this substance represents a redox shuttle that facilitates metal respiration.
Myers
Charles R
CR
Department of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Watertown Plank Rd., Milwaukee, WI 53226, USA. cmyers@mcw.edu
Myers
Judith M
JM
D004579:Electron Transport; D005290:Ferric Compounds / Q000378:metabolism; D005650:Fumarates / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D007700:Kinetics; D009566:Nitrates / Q000378:metabolism; D010084:Oxidation-Reduction; D020592:Shewanella / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D024482:Vitamin K 2 / Q000378:metabolism*
D005290:Ferric Compounds; D005650:Fumarates; D009566:Nitrates; D024482:Vitamin K 2; C025314:ferric citrate; C032005:fumaric acid; D007501:Iron