Identification and characterization of antimicrobial peptide produced by indigenously isolated Bacillus paralicheniformis UBBLi30 strain

The antimicrobial compound produced by Bacillus paralicheniformis UBBLi30 showed UV spectra absorption at 208 nm. Fourier transform infrared (FTIR) revealed characteristic bands for aliphatic chain related to hydrophobic amino acids (L-isoleucine/L-leucine) (3068, 2965 and 2871 cm⁻¹) and peptide bonds (1538, 1667 and 3312 cm⁻¹). The proton nuclear magnetic resonance (¹H NMR) showed signals for aromatic amino acid (6.5–9.5 ppm) and alkyl amines (3–4 ppm). The results of carbon (¹³C) NMR showed signals for aromatic, nitro and amide compounds. Besides this, the mass fragments (1422.576 [M+H]⁺, 711.912 [M+2H]²⁺ and 475.174 [M+3H]³⁺ m/z) observed in electrospray ionization mass spectrometry (ESI-MS) were coordinated well to the fragments of polypeptide antibiotic bacitracin. The presence of bacA gene further confirmed the production of bacitracin. Bacitracin inhibited the growth of a range of Gram-positive bacteria such as Micrococcus luteus, methicillin-resistant Staphylococcus aureus (MRSA), S. aureus, Streptococcus pyogenes and Propionibacterium acnes, and biofilm formation of M. luteus and MRSA. Moreover, this polypeptide reduced the zeta potential of M. luteus and MRSA, indicating the electrostatic sorption on bacterial surface and concentration-dependent cell membrane damages. Besides this, polypeptide showed stability in the presence of proteases (proteinase K, trypsin and pepsin), pH (1, 3, 5, 7, 9 and 11) and temperature up to 100 °C. B. paralicheniformis UBBLi30 therefore has the potential to be utilized as a bio-preservative to control the growth of spoilage and pathogenic bacteria.