Production and Characterisation of Mobilisin, a Broad-Spectrum Antimicrobial Peptide from Bacillus mobilis

Antimicrobial peptides offer significant potential in addressing antimicrobial resistance, as pathogens develop low or no resistance against them. This study aimed to isolate and screen AMP-producing bacteria from environmental samples with broad-spectrum antibacterial activity. Preliminary screening yielded 185 AMP-producing bacterial isolates and subsequently, the most promising isolate with broad-spectrum antibacterial activity was identified as Bacillus mobilis by 16S rRNA sequencing. The AMP from B. mobilis was named mobilisin and purified by hydrophobic adsorption chromatography using Diaion HP-20, followed by RP-HPLC. The molecular weight and probable sequence of mobilisin were observed to be 861.16 Da and KNMFPPK, respectively, using LC-MS/MS and PEAKS Studio 11 analysis. The purified mobilisin showed a notable antibacterial spectrum against both Gram-negative and Gram-positive bacteria with MICs of 31.25 and 62.5 µg/ml, respectively. The antibacterial potential of mobilisin was further confirmed with the synthesised peptide (KNMFPPK), which showed MIC in a similar range. The purified mobilisin exhibited thermal stability at a wide temperature range (4 °C to 80 °C) and maintained its integrity over a broad pH (2.0-11.0) range. Mobilisin also exhibited stability in the presence of various surfactants and organic solvents. The bactericidal potential of mobilisin was confirmed in vitro by scanning electron microscopy (SEM), where it displayed high efficacy by destroying the cell membrane integrity of both Gram-positive and Gram-negative bacteria. The purified mobilisin further demonstrated its applicability in fresh produce preservation by inhibiting the growth of Gram-negative and Gram-positive bacteria on strawberry fruits. Given its broad-spectrum antibacterial properties and biochemical resilience, mobilisin holds the potential for diverse applications in the pharmaceutical and food sectors.