Production of Hydrogen Sulfide from Sulfur-Containing Compounds by Various Bacteria. I. Experiments with Beef Infusion Agar Basic Medium. ∗

Discussion and Summary

1. None of the 22 strains of bacteria studied failed to produce hydrogen sulfide from beef infusion agar slants supplemented with cystine and cysteine. The latter may have been partially oxidized to cystine during autoclaving and incubation. From these data we cannot state whether the reduced or oxidized form of cystine is the immediate precursor for hydrogen sulfide formation. 2. The benzylation of the sulfhydryl group of cysteine did not prevent the desulfurization of the molecule by these bacteria, with the possible exception of M. tuberculosis and the two strains of S. aureus. The volatile decomposition product of S-benzyl-cysteine which reacted with the lead acetate paper was possibly benzyl mercaptan. 3. Hydrogen sulfide was produced from N-benzoyl-cysteine slants only by Proteus X-19 and OX-2, K. pneu-moniae, type B, and the two strains of S. aureus, while none of the bacteria was able to metabolize N,N-dibenzoyl-cystine with hydrogen sulfide formation. It appears, therefore, that benzoylation of the alpha amino groups prevents the evolution of hydrogen sulfide from cystine. If as proposed by Desnuelle for Escherkhia coli, 5 the reduction of cystine to cysteine is a necessary step for the production of hydrogen sulfide, it may be that blocking of the amino groups of cystine prevents the conversion of the disulfide to the sulfhydryl form. This would be contrary to the results of experiments with animals by Lewis, Updegraff, and McGinty 6 who administered N,N-dibenzoyl-cystine and recovered N-benzoyl-cysteine from the urine. Some bacteria are apparently able to use the sulfhydryl group of the benzoylated cysteine for hydrogen sulfide production.

4. None of the bacteria studied utilized the sulfur of cysteic acid, methionine, or S-benzyl-homocysteine for hydrogen sulfide or mercaptan formation. It seems that methionine is not converted to cystine or cysteine by these organisms prior to its possible utilization. Similar conclusions were reached in studies with Bad. tularense. 4