Screening and characterisation of petroleum hydrocarbon-degrading bacteria isolated from petroleum-contaminated soil...

Remediating petroleum-contaminated soils from oil fields is one of the most challenging tasks for both the Libyan oil sector and the global oil industry. It is therefore necessary to isolate and identify bacteria capable of metabolically synthesising biosurfactants from oil-contaminated soil, as they can be used for bioremediation. Two bacterial strains, which degrade petroleum hydrocarbons and produce biosurfactants, were isolated from oil-contaminated soils in the southern Sirte basin in central North Libya, using an enrichment technique. Morphological, biochemical, and 16S rRNA analyses indicated that the isolates are more likely to be of the species Dietzia cinnamea and Rhodococcus pyridinivorans. The biodegradation efficiency (BE) of crude oil and diesel oil separately (1% v/v) was evaluated after 14 days of incubation for both strains using the GC-FID technique. The strains effectively degraded 91.87% and 75.35% of the crude oil. Whereas for diesel oil, they displayed a lower BE of 87.61% and 70.14%, respectively. Multiple screening tests were then used to check for the production of bioemulsifiers in the bacterial isolates. The drop collapse test was positive for both bacteria tested, collapsing the culture supernatant in less than 30 s. The oil spread test performed with crude oil showed a clear zone of 2.98 ± 0.02 cm and 2.71 ± 0.04 cm in diameter, respectively. Furthermore, the emulsification index (E₂₄) of biosurfactant against diesel oil was measured to be 34 ± 0.17% and 30.8 ± 0.3%, respectively. It was found that biosurfactants can enhance the efficiency of oil degradation, which makes them attractive for future application in the MEOR (microbial enhanced oil recovery) process. Therefore, it has potential applications in bioremediation.