Response Surface Optimization of Culture Conditions for Cyclic Lipopeptide MS07 from Bacillus siamensis Reveals Diverse Insights Targeting Antimicrobial and Antibiofilm Activity

Abstract

Efforts to isolate a broad-spectrum antimicrobial peptide (AMP) from microbial sources have been on the rise recently. Here, we report the identification, the optimization of the culture conditions, and the characterization of an efficient AMP from the Bacillus strain designated MS07 that exhibits antimicrobial and antibiofilm activity. The production of MS07 was maximized by evaluating the culture conditions by the response surface methodology to obtain optimum media compositions. The biochemical integrity of MS07 was assessed by a bioassay indicating inhibition at ~6 kDa, like tricine-SDS-PAGE. MALDI-TOF confirmed the molecular weight and purity, showing a molecular mass of 6.099 kDa. Peptide MS07 exhibited antimicrobial activity against both Gram-positive and Gram-negative bacteria. The MIC of MS07 for Escherichia coli, Alcaligenes faecalis, MRSA, and Pseudomonas aeruginosa ranged from 16–32 µg/mL, demonstrating superior potency. The biomass was diminished by about 15% and 11%, with rising concentrations up to 8 × MIC, for P. aeruginosa and E. coli biofilm, respectively. MS07 exhibited an 8 µM and 6 µM minimum bactericidal concentration against the biofilm of the Gram-negative strains P. aeruginosa and E. coli, respectively. Peptide MS07 reduced and interrupted the biofilm development in a concentration-dependent manner, as determined by BacLight live/dead staining using confocal microscopy.