Sulfidogenesis from 2-aminoethanesulfonate (taurine) fermentation by a morphologically unusual sulfate-reducing bacterium, Desulforhopalus singaporensis sp nov.

A pure culture of an obligately anaerobic marine bacterium was obtained fro m an anaerobic enrichment culture in which taurine (2-aminoethanesulfonate) was the sole source of carbon, energy, and nitrogen, Taurine fermentation resulted in acetate, ammonia, and sulfide as end products. Other sulfonates , including 2-hydroxyethanesulfonate (isethionate) and cysteate (alanine-3- sulfonate), were not fermented. When malate was the sole source of carbon a nd energy, the bacterium reduced sulfate, sulfite, thiosulfate, or nitrate (reduced to ammonia) but did not use fumarate or dimethyl sulfoxide as a te rminal electron acceptor for growth. Taurine-grown cells had significantly lower adenylylphosphosulfate reductase activities than sulfate-grown cells had, which was consistent with the notion that sulfate was not released as a result of oxidative C-S bond cleavage and then assimilated. The name Desu lforhopalus singaporensis is proposed for this sulfate-reducing bacterium, which is morphologically unusual compared to the previously described sulfa te-reducing bacteria by virtue of the spinae present on the rod-shaped, gra m-negative, nonmotile cells; endospore formation was not discerned, nor was desulfoviridin detected. Granules of poly-beta-hgdroxybutyrate were abunda nt in taurine-grown cells. This organism shares with the other member of th e genus Desulforhopalus which has been described a unique 13-base deletion in the 16S ribosomal DNA. It differs in several ways from a recently descri bed endospore-forming anaerobe (K. Denger, H. Laue, and A. M. Cook, Arch. M icrobiol. 168:297-301, 1997) that reportedly produces thiosulfate but not s ulfide from taurine fermentation. D. singaporensis thus appears to be the f irst example of an organism which exhibits sulfidogenesis during taurine fe rmentation. Implications for sulfonate sulfur in the sulfur cycle are discu ssed.