TAURINE REDUCTION IN ANAEROBIC RESPIRATION OF BILOPHILA-WADSWORTHIA RZATAU

Organosulfonates are important natural and man-made compounds, but unt il recently (T, J, Lie, T, Pitta, E. R. Leadbetter, W. Godchaux III, a nd J. R. Leadbetter. Arch, Microbiol. 166:201-210, 1996), they were no t believed to be dissimilated under anoxic conditions. We also chose t o test whether alkane- and arenesulfonates could serve as electron sin ks in respiratory metabolism. We generated 60 anoxic enrichment cultur es in mineral salts medium which included several potential electron d onors and a single organic sulfonate as an electron sink, and we used material from anaerobic digestors in communal sewage works as inocula, None of the four aromatic sulfonates, the three unsubstituted alkanes ulfonates, or the N-sulfonate tested gave positive enrichment cultures requiring both the electron donor and electron sink for growth. Nine cultures utilizing the natural products taurine, cysteate, or isethion ate were considered positive for growth, and all formed sulfide. Two c learly different pure cultures were examined. Putative Desulfovibrio s p, strain RZACYSA, with lactate as the electron donor, utilized sulfat e, aminomeathanesulfonate, taurine, isethionate, and cysteate, convert ing tile latter to ammonia, acetate, and sulfide, Strain RZATAU was id entified by 16S rDNA analysis as Bilophila wadsworthia. Ire the presen ce of, e.g., formate as the electron donor, it utilized, e.g., cysteat e and isethionate and converted taurine quantitatively to cell materia l and products identified as ammonia, acetate, and sulfide. Sulfite an d thiosulfate, but not sulfate, were utilized as electron sinks, as wa s nitrate, when lactate was provided as the electron donor and carbon source. A growth requirement for 1,4-naphahoquinone indicates a menaqu inone electron carrier, and the presence of cytochrome c supports the presence of an electron transport chain, Pyruvate-dependent disappeara nce of taurine from cell extracts, as well as formation of alanine and release of ammonia and acetate, was detected. We suspected that sulfi te is an intermediate, and we detected desulfoviridin (sulfite reducta se). We thus believe that sulfonate reduction is one aspect of a respi ratory system transferring electrons from, e.g., formate to sulfate re ductase via an electron transport system which presumablygenerates a p roton gradient across the cell membrane.