Virgicin, a Novel Lanthipeptide from Virgibacillus Sp. Strain AK90 Exhibits Inhibitory Activity Against Gram-positive Bacteria

There is a significant increase in the discovery of new antimicrobial compounds in recent past to combat drug resistant pathogens. Members of the genus Bacillus and related genera have been screened extensively due to their ability to produce wide range of antimicrobial compounds. In this study, we have isolated and characterized a new antimicrobial peptide from a marine bacterium identified as Virgibacillus species. The low molecular mass and stability of the antimicrobial substance pointed towards the bacteriocinogenic nature of the compound. The RAST analysis of genome sequence showed presence of a putative bacteriocin biosynthetic cluster containing genes necessary for synthesis of a lanthipeptide. Translated amino acid sequence of mature C-terminal propeptide showed identity with salivaricin A (52.2%) and lacticin A (33.3%). Accordingly, the mass (2417 Da) obtained by MALDI analysis was in agreement with posttranslational modifications of the leader peptide to yield three methyl lanthionine rings and a disulfide bond between two free cysteine residues. The lanthipeptide was named as virgicin, which selectively inhibited the growth of Gram-positive bacteria and biofilm formation by Enterococcus faecalis. Inhibition of biofilm formation by E. faecalis was also observed in in vitro model experiments using hydroxyapatite discs. Thus, virgicin appears to be a promising new bacteriocin to control oral biofilm formation by selective pathogens.