Biosurfactant Production by Bacillus tequilensis?ZSB10: Structural Characterization,Physicochemical, and Antifungal Properties

A new biosurfactant was obtained from a moderately halophilic bacterium identified as Bacillus tequilensis ZSB10 that was isolated from a saline water pond located in Tehuacan-Cuicatlan valley, Mexico. A kinetic analysis of the bacterial growth of the ZSB10 strain showed a maximum growth at 24 h regardless of the initial pH (5, 7.4, and 9). The best results were found at pH = 7.4 in terms of bacterial growth, besides which the produced biosurfactant showed emulsifying and surfactant properties with an emulsification index (E₂₄) and surface tension change (ΔST) of 54 ± 0% and 26 mN m^?1, respectively. Extracted ZSB10 crude biosurfactant had a yield of 106 ± 6 mg L^?1, an E₂₄ = 58.4 ± 0.2%, and a ΔST = 26 mN m^?1 with a critical micelle concentration (CMC) of 44.82 mg L^?1. Also, its structure was characterized by MALDI-TOF mass spectrometry as a surfactin, iturin A, and fengycin mixture whose main isoform was leu/ile-7 C₁₅ surfactin M + Na]⁺. Finally, the ZSB10 crude biosurfactant showed antifungal activity against Helminthosporium sp., with a 79.3% growth inhibition and an IC₅₀ of 1.37 mg per disc. Therefore, this biosurfactant could be used as biopesticide.