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Applied and Environmental Microbiology, September 2004, p. 5415-5425, Vol. 70, No. 9
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.9.5415-5425.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Shewanella oneidensis MR-1 Restores Menaquinone Synthesis to a Menaquinone-Negative Mutant

Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin

Received 10 February 2004/ Accepted 14 May 2004

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.

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