Molecular and functional characterization of Bacillus Lipopeptides: Cytotoxicity, antioxidant potential, and mechanistic antimicrobial Action

Microbial lipopeptides are promising bioactive compounds with potential applications in food, nutraceutical, and therapeutic fields due to their biological activities. In this study, we evaluated two lipopeptide-producing strains, H6 and S15, focusing on their cytotoxic, antioxidant/pro-oxidant behavior, and antimicrobial effects against bacterial and fungal pathogens. HT-29 and Caco-2 cell models were employed to assess cytotoxicity, revealing minimal effects at low concentrations (≤20 μg/mL) and dose-dependent reductions in cell viability at higher doses, accompanied by marked increases in intracellular reactive oxygen species (ROS). Cellular antioxidant activity evaluated in human erythrocytes (CAA-RBC assay) demonstrated that both compounds exhibit membrane-protective antioxidant effects at non-cytotoxic concentrations, with S15 showing superior activity. Antibacterial assays indicated strong, concentration-dependent activity preferentially against Gram-positive bacteria, while molecular docking revealed that fengycin homologs interact with β-tubulin and bacterial GyrB, suggesting additional intracellular targets. Antifungal docking studies further demonstrated that shorter-chain fengycins (C13–C15) have higher binding affinity and optimal interactions with β-tubulin. Collectively, these results highlight the dual pro-oxidant and antioxidant nature of H6 and S15, their potent antimicrobial effects, and the importance of structural features in determining bioactivity. These results highlight the potential of these biosurfactants for use as functional food additives, nutraceutical ingredients, and antimicrobial agents.