Enhancement of oil biodegradation by using the biosurfactant produced from local Bacillus subtilis isolate

Background: Oil contamination poses a significant threat to the global environment and has attracted widespread attention in recent years. Given its significance, further exploration of biodegradation options for this contamination has never been more crucial than it is today. Therefore, the objective of the study was to improve the biodegradation of oil by utilizing local bacterial isolates alongside a biosurfactant produced by a Bacillus subtilis isolate. Twenty-two bacterial isolates were collected from four samples of hydrocarbon-contaminated soil. These isolates underwent screening to assess their effectiveness in degrading crude oil using two distinct methods.Methods: Soli samples were collected from two contaminated sites with oil pollutants in Baghdad city. Biodegradation ability was tested on liquid Bushnell Haas medium (BH), pH 7 supplemented with 1% of crude oil and then screened primarily using the 2,6-dichlorophenol indophenol method to determine the ability of isolates to degrade the crude oil. All isolates were identified morphologically and biochemically. Biosurfactants was extracted from Bacillus subtilis previously isolated.Results: Isolate SCS1 has appeared the highest ability reaching 52.6% compared with other isolates, also, the results of secondary screening confirmed that isolate SCS1 has given the best biodegradation reaching 53.8%. The isolate SCS1 was identified as Pseudomonas aeruginosa, this isolate was used to study the effect of biosurfactant on crude oil biodegradation. Results exhibited a high biodegradation efficiency reaching 85.1% in culture broths supplemented with 100 mg/100. It was noted that the use of 150 and 200 mg of biosurfactant led to a decrease in the biodegradation of crude oil.Conclusion: The use of biosurfactant led to an increase in the degradation rate by up to 61.7% of crude oil by Pseudomonas aeruginosa when using 25-100 mg of crude biosurfactant that produced by local isolate Bacillus subtilis.Keywords: Biodegradation; Biosurfactant; Bacillus subtilis; Pseudomonas aeruginosa