Purpose: This self-lethality phenotype is rarely observed in bacteriocin-producers because immunity proteins are generally co-transcribed with the bacteriocin structural gene. Additionally, no mutations or atypical gene arrangements were observed within the gene cluster for munL. Therefore, the objective of this study was to identify the component(s) causing the self-lethality.
Methods: The supernatant from an 18-hour culture of E. mundtii CUFG08 was filter-sterilized and applied to a SepPak C18 solid phase extraction cartridge. The fraction eluted via 50% isopropanol was applied to a cation-exchange column, and the non-retained portion was applied to a 250 mm x 4.6 mm Jupiter 5 µ C5 300 Å column connected to an Agilent 1100 HPLC. The peak that contained the bacteriocin activity was collected and sequenced using trypsin digestion and MS/MS for amino acid sequencing.
Results: The isolated compound was found to be a 50-residue peptide, designated mundticin K (munK). This mature peptide is identical to mundticin KS (munKS), except that munKS is cleaved after the double-glycine motif, resembling other class IIa bacteriocins. MunK contains an additional 7-residue N-terminal sequence including the double-glycine motif, which is longer than the mature 43-residue munKS.
Significance: This data may be used to discover more information on the mechanism of action of class IIa bacteriocins, the maturation process, and the mechanism of the immunity protein. It may also help increase the understanding of how sensitive strains, such as L. monocytogenes, develop resistance to class IIa bacteriocins.