Purification and Characterization of Streptin, a Type A1 Lantibiotic Produced by Streptococcus pyogenes

Abstract

ABSTRACT Approximately 10% of Streptococcus pyogenes strains inhibit the growth of all nine indicators in a standardized streptococcal bacteriocin typing scheme. The present study has shown that this inhibitory profile, referred to as bacteriocin producer (P)-type 777 activity, is due to the type A1 lantibiotic streptin. Two major forms of streptin were purified to homogeneity from 95% acidified (pH 2) methanol extracts of S. pyogenes M25 cells by using a series of reversed-phase chromatographic separations. The fully processed form of streptin (streptin 1) is a 23-amino-acid peptide with a mass of 2,424 Da. The 2,821- M r form of the peptide (streptin 2) has three additional amino acids (TPY) at the N terminus. Strain M25 extracts also contained small quantities of the streptin 1 and streptin 2 peptides in various stages of dehydration. Streptin 1 and streptin 2 were each capable of specifically inducing streptin production when added to strain M25 cultures. The streptin gene cluster resembled that of other type A1 lantibiotics but appeared to lack a streptin-specific proteinase gene. Although the streptin structural gene ( srtA ) was widespread within S. pyogenes , being detected in 40 of 58 strains, each representing a different M serotype, only 10 of these srtA -positive strains produced active streptin. The failure of some strains to express streptin was attributed to an ∼4.5-kb deletion in their streptin loci, encompassing genes putatively encoding proteins involved in streptin processing ( srtB and srtC ) and transport ( srtT ). In other strains, srtA transcription appeared to be defective. No direct association could be detected between the production of streptin and the production of the lantibiotic-like hemolysin streptolysin S in strain M25.