Identification and molecular analysis of βC–S lyase producing hydrogen sulfide in Streptococcus intermedius

Abstract

Hydrogen sulfide (H2S) is a toxic gas that induces the modification and release of haemoglobin in erythrocytes; however, it also functions in methionine biosynthesis in bacteria.βC–S lyase, encoded by thelcdgene, is responsible for bacterial H2S production through the cleavage ofl-cysteine. In this study, 26 of 29 crude extracts from reference and clinical strains ofStreptococcus intermediusproduced H2S froml-cysteine. The capacities in those strains were not higher than those in strains of the other anginosus group of streptococci,Streptococcus anginosusandStreptococcus constellatus, but were much greater than those in strains ofStreptococcus gordonii, which is known to have an extremely low capacity for H2S production. Incubation of the remaining three extracts withl-cysteine did not result in H2S production. Sequence analysis revealed that thelcdgenes from these three strains (S. intermediusstrains ATCC 27335, IMU151 and IMU202) contained mutations or small deletions. H2S production in crude extracts prepared fromS. intermediusATCC 27335 was restored by repairing thelcdgene sequence in genomic DNA. The kinetic properties of the purified recombinant protein encoded by the repairedlcdgene were comparable to those of native proteins produced by H2S-producing strains, whereas the truncated protein produced byS. intermediusATCC 27335 had no enzymic activity withl-cysteine orl-cystathionine. However, real-time PCR analysis indicated that thelcdgene in strains ATCC 27335, IMU151 and IMU202 is transcribed and regulated in a manner similar to that in the H2S-producing strain.