Genome mining of Bacillus licheniformis MCC2514 for the identification of lasso peptide biosynthetic gene cluster and its characterization.

The probiotic strain Bacillus licheniformis MCC2514 has been shown to produce a strong antibacterial peptide and the whole
genome sequence of this strain is also reported in our previous study. The present study is focused on the genome level
investigation of this peptide antibiotic and its characterization. Genome mining of the culture revealed the presence of three
putative bacteriocin clusters, viz. lichenicidin, sonorensin and lasso peptide. Hence, the mode of action of the peptide was
investigated by reporter assay, scanning electron microscopy, and Fourier Transform Infrared spectroscopy. Additionally,
the peptide treated groups of Kocuria rhizophila showed a reduction in the fold expression for transcription-related genes.
The gene expression studies, quantitative β-galactosidase induction assay using the RNA stress reporter strain, yvgS along
with the homology studies concluded that lasso peptide is responsible for the antibacterial activity of the peptide which acts
as an inhibitor of RNA biosynthesis. Gene expression analysis showed a considerable increase in fold expression of lasso
peptide genes at various fermentation hours. Also, the peptide was isolated, and its time-kill kinetics and minimum inhibitory
concentration against the indicator pathogen K. rhizophila were examined. The peptide was also purified and the molecular
weight was determined to be ~ 2 kDa. Our study suggests that this bacteriocin can function as an effective antibacterial agent
in food products as well as in therapeutics as it contains lasso peptide, which inhibits the RNA biosynthesis.