Evaluation of biosurfactant producing activity of Bacillus thuringiensis-VITNDUVNB04 isolated from oil contaminated soil by various methods

Biosurfactants are the surface active molecules that are produced by microorganisms. The present study focused on the isolation of biosurfactant producing bacteria from oil contaminated soil samples of an automobile mechanical workshop near VIT University, Vellore. A total of 5 bacterial colonies were isolated from the collected samples (DNT-1 to DNT-5). Among them the isolate DNT-2 showed maximum biosurfactant production followed by DNT-3 and DNT-5. In primary screening DNT-2 showed a good haemolytic activity with a zone of clearance of 18 mm followed by DNT-3 (12 mm) and DNT-5 (10 mm). All three isolates were positive for lipase production and capable of degrading tributyrin. In the secondary screening method, DNT-2 showed high activity with 22 mm of oil spreading activity and 20 mm of drop collapsing activity. The emulsifying capacity of DNT-3, DNT-2 and DNT-5 was evaluated using E24 emulsification index where isolates showed 52%, 86% and 43% of activity respectively. Among all the isolates DNT-2 showed high surfactant production in all screening assays. Potential isolate DNT-2 was identified as Bacillus thuringiensis using biochemical tests and molecular 16s r RNA sequencing analysis.