Screening of biosurfactant-producing bacteria from petroleum-contaminated samples and optimization of fermentation conditions

Abstract In petroleum contamination bioremediation, the difficulties in screening efficient biosurfactant-producing bacteria, their low yields, and unsatisfactory remediation effects have limited practical applications. The study employed the “transparent zone preliminary screening–surface tension/emulsification activity re-screening” strategy to test samples from polluted petroleum environments. This strategy combines the “rapid identification of potential strains” with “precise quantification of activity”, avoiding the problems of missed or incorrect screening in traditional single-screening methods, significantly enhancing the efficiency and accuracy of screening for highly productive strains, and simultaneously conducting product identification, fermentation optimization, and soil pollution remediation experiments. Results show that oilfield soil is the best source of biosurfactant-producing bacteria. Bacillus subtilis screened from this source produces a lipopeptide-type biosurfactant, with a minimum surface tension of 28.5 ± 0.5 mN/m and a maximum emulsification index of 65.6 ± 0.8 %. Under optimized fermentation conditions (carbon source 2.0 %, nitrogen source 1.5 %, initial pH 7.0, 72 h of fermentation), lipopeptide yield increased significantly compared with basic conditions. In practical remediation tests, the combination of “strain + lipopeptide” reached a petroleum degradation rate of 85.5 %, which was much higher than that of the indigenous microbial group or the strain alone. The dehydrogenase activity reached 2.2 mg/g·h, indicating higher microbial metabolic efficiency. In conclusion, the screened B. subtilis and its lipopeptide biosurfactant provide quantifiable and reliable resources and technical solutions for petroleum contamination bioremediation, supporting further process optimization and industrial-scale application.