New gene cluster for lantibiotic streptin possibly involved in streptolysin S formation

Streptolysin S (SLS) is a serum-extractable and oxygen-stable hemolysin produced by Group A Streptococcus. A SLS-deficient mutant in which transposon Tn 916 was inserted in a locus distinct from the sag gene cluster [Nizet et al. (2000) Infect. Immun. 68, 4245-4254] was obtained by filter mating of the transposon-harbouring Enterococcus faecalis strain and Streptococcus pyogenes BL(T). This mutant, N22, had completely lost the hemolytic activity, in consequence of insertion of a single Tn 916 into a hitherto-unknown lantibiotic gene cluster composed of 10 open reading frames. The arrangement and sequence of this lantibiotic gene cluster were similar to those of nisin and subtilin, and so we designated this new lantibiotic as streptin. The bactericidal activity of streptin was abolished on treatment with trypsin or proteinase K. The different host range and nucleotide sequence clearly distinguished streptin from streptococcins. Streptin was not hemolytic and its bacteriocin activity was independent of carrier oligonucleotides effective for SLS. The fact that N22 also lost the anti-bacterial activity against indicator streptococci reveals that the factor(s) required for lantibiotic formation plays an important role in SLS formation as well.