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Complete Type III Secretion System of a Mesophilic Aeromonas hydrophila Strain. Silvia Vilches, 2004. Shewanella oneidensis MR-1 Restores Menaquinone Synthesis to a Menaquinone-Negative Mutant. Charles R. Myers, 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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