Antibacterial Activities of Predicted AMP in Lactiplantibacillus plantarum K9

This study aimed to identify novel antimicrobial peptides (AMPs) from Lactiplantibacillus plantarum K9, isolated from Protaetia brevitarsis seulensis larvae, using genome and transcriptome analyses. L. plantarum K9, among the isolated lactic acid bacteria from P. brevitarsis larvae, showed the strongest antimicrobial activity, with MIC₉₀ values of 22 μL against E. coli and 21 μL against S. aureus. Approximately 54% of the antimicrobial activity was attributed to peptides or proteins. Genome analysis revealed a 3 Mb chromosome and three plasmids. Screening of hypothetical proteins using CAMP_R4 identified 18 AMP candidates. Transcriptomic analysis showed that most AMP genes were more highly expressed in the stationary phase and were upregulated under low-pH conditions. Antimicrobial assays using synthetic peptides demonstrated that AMP4, 6, 7, 12-2, 14, and 18 exhibited strong activity against S. aureus, whereas AMP16 and 18 were effective against E. coli. After cloning each AMP and assessing its antimicrobial activity, the cloned AMPs exhibited overall greater antimicrobial activity against S. aureus than against E. coli. Among all candidates, AMP12 displayed the strongest antimicrobial activity and high specificity toward S. aureus. Structural analysis revealed a conserved α-helical region that is likely responsible for membrane-targeting antimicrobial activity. Collectively, these findings suggest that L. plantarum K9 AMP12 is a novel antimicrobial peptide that contributes to the strain's antimicrobial properties.