To adapt to external stimuli, bacteria fine-tune important protein activities using post-translational modifications. The present study provides novel insights into the molecular mechanism of the antimicrobial peptide BCp12. We demonstrate that BCp12 significantly suppressed bacterial growth, induced cell apoptosis, and modulated overall malonylation levels in Staphylococcus aureus cells. Malonylateomic analysis was performed to identify the proteins malonylated by the BCp12 treatment of S. aureus. In total, 53 malonylated proteins (17 up-regulated, 36 down-regulated) were identified as differentially expressed malonylated proteins (DMPs; > 1.5-fold or <0.67-fold, P < 0.05). This result was confirmed via the identification of 21 differential metabolites (DMs; VIP > 1, P < 0.05) in the arginine and proline metabolome. Bioinformatic analysis revealed that the DMPs and DMs were especially enriched in the arginine synthesis pathway. By integrating our lysine malonylational and metabolomic data, we provide new insights into the mechanism by which BCp12 inhibits S. aureus.

Aims Staphylococcus aureus has emerged as a serious threat to food safety owing to biofilm formation. The study aimed to examine the antibiofilm mechanism of a novel milk‐derived antimicrobial peptide BCp12 against it. Methods and results Antibiofilm activity of BCp12 was studied by crystal violet staining, MTT assay, motility, SEM and CLSM. TMT proteome, real‐time PCR and molecular docking in silico were conducted to evaluate the mechanism of BCp12 against S. aureus biofilm. The results showed that BCp12 had significant antibiofilm activity at 1 × MIC and sub‐MIC. BCp12 induced the dispersion of structure of S. aureus biofilm BCp12 inhibited the movement of S. aureus. A total of 703 proteins were downregulated and 334 proteins were upregulated after BCp12 treatment. The proteins (agrA, agrB, agrC and psmβ) of the QS systems were downregulated. Additionally, the expression of the agr‐related genes, agrA, agrB, agrC and psmβ, was downregulated. BCp12 was bound to the receptor proteins agrA and agrC through hydrogen bonds and π–π bonds. Conclusions The results showed the antibiofilm activity of BCp12 and it inhibits the biofilm formation by interfering agr QS system. Significance and Impact of Study BCp12 has the potential to be a novel antibiofilm agent against S. aureus biofilm and used in the food industry.

BCp12 is a novel casein-derived antibacterial peptide with a broad-spectrum antibacterial effect. However, its action mechanism against E. coli is unknown. In this study, the growth curve showed that BCp12 had excellent antibacterial activity against E. coli. Red (propidium iodide staining) and green (fluorescein isothiocyanate staining) fluorescence signals were detected at the edges of the E. coli cells treated with BCp12. scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that E. coli cells became rough and shrunken, and part of the cell contents leaked to form a cavity. Furthermore, the iTRAQ proteome analysis showed that 193 and 174 proteins were significantly up-regulated and down-regulated, respectively, after BCp12 treatment. Four enzymes involved in fatty acid degradation of E. coli were down-regulated, disrupting the synthesis of cell membranes. Molecular docking and gel retardation assays showed that BCp12 could bind to genes encoding four key enzymes involved in the fatty acid degradation pathway through hydrogen bonding and hydrophobic interactions, thus significantly inhibiting their activities. Overall, the results indicate that BCp12 inhibits the growth of E. coli, causing metabolic disorders, thus destroying the structure of cell membranes.