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

¹ Department of Dental Pharmacology, Iwate Medical University School of Dentistry, Morioka, Japan

² Department of Periodontology, Iwate Medical University School of Dentistry, Morioka, Japan

³ Department of Biological Science and Technology, Life System, Institute of Technology and Science, University of Tokushima Graduate School, Tokushima, Japan

Correspondence
Yasuo Yoshida
yasuoy{at}iwate-med.ac.jp

Received March 31, 2008
Accepted August 5, 2008

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 the lcd gene, is responsible for bacterial H₂S production through the cleavage of L-cysteine. In this study, 26 of 29 crude extracts from reference and clinical strains of Streptococcus intermedius produced H₂S 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 H₂S production. Incubation of the remaining three extracts with L-cysteine did not result in H₂S 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. H₂S 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 H₂S-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 H₂S-producing strain.

Abbreviations: PLP, pyridoxal 5'-phosphate; GST, glutathione S-transferase.

The GenBank/EMBL/DDBJ accession numbers for the lcd sequences of S. intermedius strains ATCC 27335, IMU202, IMU151, IMU105, IMU122, IMU201 and DP102 are AB381917, AB381918, AB381919, AB381920, AB381921, AB381922 and AB381923, respectively.