Abstract: A mutant strain named BV227 with higher yield of antimicrobial lipopeptides was obtained from Bacillus velezensis BVQ121, a strain producing lipopeptides, by atmospheric and room temperature plasma (ARTP)-LiCl mutagenesis. Under optimized fermentation conditions, BV227 produced 122.31% more lipopeptides than did BVQ121. Liquid chromatography-mass spectrometry (LC-MS), whole-genome sequencing, and transcriptome analysis revealed that: 1) the mutant strain produced more types and larger amounts of fengycin homologs; 2) four key nonsynonymous single-nucleotide polymorphisms (SNPs) significantly affected the lipopeptide biosynthetic pathway; 3) genes involved in quorum sensing were significantly enriched; and 4) the alcohol dehydrogenase and fatty acid hydroxylase genes were significantly up-regulated, enhancing fatty acid precursor supply and increasing the structural diversity and bioactivity of lipopeptide. Antimicrobial assays using the Oxford cup method confirmed that the lipopeptides produced by the mutant strain exhibited strong inhibitory effects against Salmonella sp. and Edwardsiella ictaluri, and demonstrated excellent thermal stability. In summary, the mutant strain, in comparison to the parental strain, had an enhanced ability to produce lipopeptides under optimized fermentation conditions. Our findings confirmed the influence of genomic variation on the expression of key genes related to the synthesis of antimicrobial lipopeptides. This study provides a molecular foundation for establishing gene expression regulatory networks and rationally designing metabolic engineering strategies, and also offers a theoretical basis for the large-scale application of B. velezensis in food preservation and other fields.

Key words: atmospheric and room temperature plasma-LiCl mutagenesis, Bacillus velezensis, antimicrobial lipopeptides, genomic analysis