Optimization of biosurfactant production from chemically mutated strain of Bacillus subtilis using waste automobile oil as low-cost substrate

Abstract

In this study, we have evaluated biosurfactant production potential of locally isolated strain of Bacillus subtilis (accession # KX788864) using waste automobile oil as cost-effective substrate with waste-to-value nexus. The wild strain of B. subtilis yielded 2.1 g/L biosurfactant, showed 42% emulsification index, and 38.27 cm2 of total oil displacement. The ethidium bromide (EtBr) mutagenesis was performed by exposing native B. subtilis strain with varying concentrations of EtBr (50, 100, 150 and 200 µg/10 mL) for different time intervals of 30, 60 and 90 min. Significantly higher yield (4.2 g/L) was attained from B. subtilis MS1 exposed to EtBr (50 µg/10 mL) for 60 min confirming the positive effect of mutagenesis. The mutated strain (B. subtilis MS1) showed improved emulsification index (50.53%) and oil displacement (49.32 cm2). Fourier-transform infrared (FTIR) spectroscopy analysis of biosurfactant produced from mutated strain (B. subtilis MS1) confirmed the lipopeptide nature of biosurfactant due to the existence of amide, amine and phospholipids functional groups. The maximum surfactant yielding mutant was proceeded for optimization using response surface methodology (RSM) technique and the interaction effect of different parameters was studied that allow biosurfactant hyperproduction. After optimization, maximum biosurfactant (4.7 g/L) was obtained at pH 7, temperature 35 °C, inoculum size 3 mL and an overall incubation of 120 h. In conclusion, the economical production of biosurfactant, along with novel functional properties (i.e., oil/hydrocarbon recovery and emulsification properties), this research may be valuable for numerous bioremediation and industrial biotechnological applications.