Potential of Crude and Diesel Oil Biodegradation by Two Indigenous Nitrogen‐Fixing Bacteria Isolated From Oil‐Polluted Soil in the Sirte Basin, Libya

Bioremediation is a commonly applied, cost‐effective and environmentally friendly treatment for soils contaminated with petrogenic hydrocarbons. However, this method has not yet been widely used in Libya to treat oil‐contaminated soil, particularly in the Sirte Sedimentary Basin. In this study, the enrichment approach was used to isolate three hydrocarbon‐degrading bacteria, designated A‐1, A‐2 and A‐3, from petroleum‐affected soil in Libya’s Sirte sedimentary basin. Based on phenotypic and genetic traits, the isolates belonged to three genera and were identified as Azospirillum sp. , Microbacterium sp. and Mesorhizobium sp. respectively. An assessment of the ability of the isolated bacteria to utilise crude and diesel oil as hydrocarbon substrates revealed growth accompanied by varying rates of degradation, as determined by turbidity, residual oil concentration measurements and screening for biosurfactant production. Gas chromatography–flame ionisation detection (GC–FID) was used to measure biodegradation efficiency (%BE). The A‐1 isolate showed the highest %BE at 68.66% for crude oil, followed by A‐2 at 46.19%, while A‐3 had the lowest at 23.4%. A‐1 and A‐2 also effectively reduced diesel oil, with BE of 66.24% and 36.21% respectively. In addition, A‐1 and A‐2 achieved complete reduction of detectable hydrocarbon components of crude oil (C7–C12 and C28–C34), while A‐3 showed disappearance of detectable hydrocarbon components C31–C34. Screening of the isolated bacteria for biosurfactant production yielded positive results across all assays used; therefore, further characterisation of the biosurfactants is highly recommended. The findings of this study provide valuable insights into the role of two indigenous nitrogen‐fixing bacteria, Azospirillum sp. and Mesorhizobium sp., as well as Microbacterium sp., in the degradation of crude and diesel oil, suggesting a promising avenue for their application as an eco‐friendly remediation approach for oil spills in production fields (in situ) in Libya.