Rapid biosynthesis of biosurfactants by Bacillus tequilensis SL9 isolated from oily sludge: Characterization, optimization, and potential applications

The demand of biosurfactants is increasing. It is of great significance to obtain nonpathogenic and high-yielding microorganisms for the industrial-scale production of biosurfactants. A biosurfactant-producing strain SL9 was isolated from oily sludge. It was identified as Bacillus tequilensis based on colonial morphology and 16S rDNA sequence analysis. The biosurfactants produced by strain SL9 was extracted by modified acid precipitation method. A mixture of C₁₂, C₁₃, C₁₄ and C₁₅ surfactin homologues was detected based on HPLC–MS analysis. The optimum production of biosurfactants occurs at pH 7.0 and in the presence of 1.0 g/L NaCl. The optimal carbon source and nitrogen source were 40.0 g/L sucrose and 4.0 g/L NaNO₃, respectively. The maximum yield of biosurfactants from strain SL9 was up to 1332.68 mg/L. Interestingly, B. tequilensis SL9 can rapidly synthesize biosurfactants with a yield of 739.36 mg/L in 12 h. The extracted biosurfactants reduced the surface tension of water from 72.1 to 27.5 mN/m with a CMC of 33 mg/L. The biosurfactants can also emulsify paraffin with a EI₂₄ value of 57.58% and keep this good emulsifying activity after 96 h. The produced biosurfactants showed antimicrobial activities against Staphylococcus aureus, Cladosporium sp. and Alternaria sp. with inhibitory rate of 75.67%, 59.07% and 22.91%, respectively. The isolated strain B. tequilensis SL9 can be a nonpathogenic producer for rapid biosynthesis of biosurfactants with a relative high yield. Strain SL9 and its biosurfactant products are promising for application in the oil exploration, bioremediation, agricultural biocontrol, and pharmaceutical industries.