Physiochemical and thermodynamic characterization of lipopeptide biosurfactant secreted by Bacillus tequilensis HK01

Abstract

An extensive investigation was applied to isolate biosurfactant producing bacteria from urban waste. Bacillus tequilensis HK01 was screened and identified as an efficient biosurfactant producer among 140 bacterial isolates. A comprehensive study was done to evaluate different aspects of the growth and biosurfactant production by this strain. Growth kinetic studies showed the fast-growing behavior of the strain. Biosurfactant production was initiated at stationary phase and reached to its maximum value of about 0.8 g l⁻¹ after 50 hours. Physiochemical characterization of the biosurfactant proved the lipopeptide structure with the critical micelle concentration of about 4.5 mg ml⁻¹. Surface excess concentration of the biosurfactant at water–air interface, apparent molar volume and standard free energy of biosurfactant micellization were determined as thermodynamic properties. Finally, a two-step experimental design was conducted to optimize culture components concentration to improve biosurfactant productivity. After screening significant culture components with Placket–Burman design, response surface method was used to optimize the concentration of essential ingredients. Optimization studies was led to 2.25 times improvement in biosurfactant production by HK01 strain.