Q-297. Characterization of Pyruvate Fermentation by Desulfovibrio desulfuricans strain G20, Desulfovibrio vulgaris Hildenborough and Their Cytochrome c3 Mutants

B. J. Giles, H-C. B. Yen, J. D. Wall;
Univ. of Missouri, Columbia, MO.

The ability of the genus Desulfovibrio to efficiently reduce sulfate renders these bacteria readily culturable and thus subject to molecular examination. An effective electron transport system is necessary for survival in environmental niches where electron acceptors are variable and also functions to alter the redox state of toxic metals rendering them insoluble. To examine the flow of electrons for sulfate and/or metal reduction, it is helpful that these bacteria can grow independently of sulfidogenesis . Fermentative growth by D. desulfuricans strain G20 and D. vulgaris offers an alternate route for electron flow and aids in identifying key steps. Our molecular study of fermentation began by comparing growth of wild type and a mutant of the type-1 tetraheme cytochrome c3 gene in G20, generated by plasmid insertion. This mutant had apparent wild-type growth on lactate/sulfate but limited growth on pyruvate/sulfate. The CycA- mutant appeared to fermented pyruvate with similar kinetics and yields as wild type. However, analysis of end products indicated differences. Neither wild type nor mutant accumulated significant H2 but substantial amounts of succinate were generated by wild type only. Some fumarate accumulated with mutant fermentation but wild type generated five-fold less. Other metabolites are being identified and quantified by HPLC and enzymatic analysis to provide net carbon and reductant balance. To complement this study, a cycA deletion of D. vulgaris was generated by marker exchange mutagenesis which displayed several phenotypic differences from the G20 CycA- mutant. The DvH mutant respired more slowly than its parental strain on both lactate/sulfate and pyruvate/sulfate. When fermenting pyruvate, the DvH CycA- surprisingly exceeded wild-type growth rate and yields, producing about 50% more cell mass. Inhibition of fermentation by end products is underway and there are clear differences between the two strains and their CycA- mutants. Also a number of enzymes which appear upregulated during fermentative growth are being mutated.