Purification and partial identification of bacteriocin ISK-1, a new lantibiotic produced by Pediococcus sp. ISK-1

Bacteriocin ISK-1 is a proteinaceous inhibitory substance produced by Pediococcus sp. ISK-1 isolated from well-aged Nukadoko. Bacteriocin ISK-1 was purified by acid treatment, ammonium sulfate precipitation, cation-exchange chromatography, and reversed-phase HPLC from the culture supernatant of Pediococcus sp. ISK-1. Purification of bacteriocin ISK-1 resulted in a 30-fold increase in the specific activity and the recovery was 17%. Molecular mass of bacteriocin ISK-1 measured by fast atom bombardment-mass spectrometry was 2,960. The amino acid composition analysis of bacteriocin ISK-1 showed that it contained unusual amino acids such as lanthionine and/or 3-methyllanthionine, which is a characteristic of lantibiotics. The N-terminal amino acid sequence analysis indicated the first seven N-terminal amino acid residues as NH2-K-K-K-S-G-V-I. The primary sequence showed significant similarity to the lantibiotics lacticin 481 from Lactococcus lactis and variacin from Micrococcus varians, which suggests that bacteriocin ISK-1 is a novel lantibiotic belonging to a lacticin-481 type.