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 (E-24) and surface tension change (Delta ST) of 54 +/- 0% and 26 mN m(-1), respectively. Extracted ZSB10 crude biosurfactant had a yield of 106 +/- 6 mg L-1, an E-24 = 58.4 +/- 0.2%, and a Delta ST = 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 C-15 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.