Rhamnolipid-like glycolipid biosurfactant mediated degradation of phenanthrene and fluoranthene by Pseudomonas aeruginosa and its impact on soil enzyme activities.

Phenanthrene (Phe) and fluoranthene (Fla) are polycyclic aromatic hydrocarbons (PAHs) known for their significant toxicity and resistance to degradation, making them biohazardous substances. This study explains the efficient degradation of Phe and Fla using two bacterial isolates-Pseudomonas aeruginosa BB-BE3, and P. aeruginosa BBBJ. These isolates produced excellent amount of rhamnolipid-like glycolipid biosurfactant, with strong emulsification activity. The isolate BB-BE3 attained degradation rates of up to 93% for Phe and 73% for Fla, while BBBJ achieved degradation rate of 81% for Phe and 76% for Fla, respectively under in vitro conditions. Both isolates were found to produce catechol 1,2 dioxygenase and catechol 2,3 dioxygenase enzymes. In microcosm study, treatment of PAH-contaminated soil with biosurfactant-producing bacterial isolates in combination with their extracted biosurfactants resulted in substantially enhanced degradation efficiencies, achieving 89-99% PAHs removal across all experimental setups compared to the control. Soil enzyme activities, including dehydrogenase and fluorescein diacetate hydrolysis, were evaluated as indicators of microbial metabolic activity. Notably, soils inoculated with biosurfactant-producing bacteria along with extracted biosurfactants exhibited elevated enzyme activities at both 15 and 30 days of incubation, reflecting sustained and robust microbial activity. Collectively, these findings demonstrate the strong potential of biosurfactant-producing bacterial isolates as an effective bioremediation strategy for the degradation of PAHs in contaminated soils.