Identification and molecular analysis of betaC-S lyase producing hydrogen sulfide in Streptococcus intermedius

Hydrogen sulfide (H(2)S) is a toxic gas that induces the modification and release of haemoglobin in erythrocytes; however, it also functions in methionine biosynthesis in bacteria. betaC-S lyase, encoded by the lcd gene, is responsible for bacterial H(2)S production through the cleavage of l-cysteine. In this study, 26 of 29 crude extracts from reference and clinical strains of Streptococcus intermedius produced H(2)S from l-cysteine. The capacities in those strains were not higher than those in strains of the other anginosus group of streptococci, Streptococcus anginosus and Streptococcus constellatus, but were much greater than those in strains of Streptococcus gordonii, which is known to have an extremely low capacity for H(2)S production. Incubation of the remaining three extracts with l-cysteine did not result in H(2)S production. Sequence analysis revealed that the lcd genes from these three strains (S. intermedius strains ATCC 27335, IMU151 and IMU202) contained mutations or small deletions. H(2)S production in crude extracts prepared from S. intermedius ATCC 27335 was restored by repairing the lcd gene sequence in genomic DNA. The kinetic properties of the purified recombinant protein encoded by the repaired lcd gene were comparable to those of native proteins produced by H(2)S-producing strains, whereas the truncated protein produced by S. intermedius ATCC 27335 had no enzymic activity with l-cysteine or l-cystathionine. However, real-time PCR analysis indicated that the lcd gene in strains ATCC 27335, IMU151 and IMU202 is transcribed and regulated in a manner similar to that in the H(2)S-producing strain.