Production and characteristics of biosurfactant produced by Bacillus pseudomycoides BS6 utilizing soybean oil waste

Bacillus pseudomycoides BS6, a bacterial strain isolated from edible oil contaminated soil, was identified to be a potent producer of biosurfactant using soybean oil waste as the sole source of carbon and energy and showed good interfacial characteristics. Crude biosurfactants were obtained from cell-free culture supernatant and was further purified by column chromatography on reverse-phase silica gel, ultra-filtration, acidification and lyophilisation. Thin-layer chromatography (TLC) and Fourier Transform Infrared Spectroscopy (FT-IR) analyses showed that the biosurfactant produced by strain BS6 was lipopeptide. The chemical structure of the purified lipopeptide was analyzed by GC-MS, amino acid analyzer and LTQ Orbitrap Elite combination mass spectrometer. It was inferred that the compound was a novel cyclic lipopeptide with a long-chain fatty acid 3-OH-C18 and a peptide comprised of five amino acids. The molar concentration of glutamic acid, methionine and lysine in the peptide chain was 19.36%, 56.32%, and 19.61%, respectively. The critical micelle concentration of the purified lipopeptide was only 56 mg l−1 and could reduce the surface tension of water from 71.6 mN m−1 to 30.2 mN m−1. Its emulsification index against five plant oils and two hydrocarbons was approximately 62.8–94.2%. All these characteristics support bioconversion by BS6 is a promising and commercial way of recycling waste cooking oil and bioremediation in petroleum-contaminated sites.