Abstract

Biosurfactants are surface-active microbial molecules with increasing industrial relevance as sustainable alternatives to synthetic surfactants. Among them, lipopeptides produced by Bacillus species, particularly surfactin, exhibit strong interfacial activity and biological functionality. In this study, rhizospheric soils from the La Araucanía region, Chile, were explored as a source of biosurfactant-producing bacteria. Eighteen strains were isolated, and two high-performing strains, Solo 1 and Solo 4, were identified as Bacillus amylolique- faciens and Bacillus subtilis, respectively. Both strains harbored the srfAA gene and pro- duced surfactin isoforms confirmed by MALDI-TOF MS. Kinetic analysis revealed distinct production profiles, with Solo 1 reaching a maximum of 90 mg L−1 at 24 h, whereas Solo 4 showed continuous production up to 224.4 mg L−1 at 72 h. Both biosurfactants exhibited high emulsification capacity (>80%) and stability across wide ranges of temperature, pH, and salinity. Importantly, cell-free supernatants from both strains showed antibacterial and antibiofilm activity against Staphylococcus aureus, with Solo 4 reaching 81% biofilm inhibition. In addition, surfactin-enriched extracts inhibited the pathogenic bacterium Pseudomonas syringae and the filamentous fungus Fusarium oxysporum, with Solo 4 consist- ently showing stronger antimicrobial performance. Overall, these findings identify Solo 4 as a promising native Bacillus strain for future development of biosurfactant-based sys- tems aimed at antimicrobial control, biofilm management, agricultural pathogen suppres- sion, surface sanitation, and environmentally compatible biotechnological processes.