Biosurfactant production and characterization of Bacillus sp ZG0427 isolated from oil-contaminated soil

An effective biosurfactant-producing strain, denoted ZG0427, was isolated from oil-contaminated soil samples collected from an oilfield in northwest China using the drop-collapse test, oil displacement test, and surface tension measurements. The strain was identified as Bacillus sp. based on the results of morphological and biochemical tests and 16S rDNA sequence analysis. The kinetics of cell growth and biosurfactant production were monitored. A maximum biosurfactant production of 2.79 g/L was achieved when the cells were cultivated in fermentation medium containing 2 % (w/v) of glucose as the sole carbon source, with shaking (180 rpm) at 37 degrees C for 32 h. The extracted biosurfactant reduced the surface tension of deionized water to 24.6 mN/m, with a critical micelle concentration of 50 mg/L, and showed a remarkable ability to reduce both surface tension and emulsification over wide ranges of pH (5.0-12.0), temperature (-70 to 121 degrees C), and NaCl concentrations (0-10 %, w/v), respectively. The biosurfactant was extracted from the culture supernatant and partially characterized as lipopeptide.