Isolation, characterization, and bioremediation potential of oil-degrading bacteria from contaminated soils in Shiraz and Bandar Abbas, Iran

Petroleum hydrocarbons are among the most persistent environmental pollutants, posing serious risks to soil and aquatic ecosystems. Bioremediation using indigenous hydrocarbon-degrading bacteria provides a cost-effective and environmentally sustainable alternative to physical and chemical treatments. In this study, oil-degrading bacteria were isolated from contaminated soils collected near oil refineries in Shiraz and Bandar Abbas, Iran, and screened for their biodegradation potential. A total of twenty-four bacterial isolates were obtained, among which four showed the highest growth rates and crude-oil degradation efficiency. These isolates were further evaluated for biosurfactant production using hemolysis, drop-collapse, oil displacement, emulsification (E24), and bacterial adherence to hydrocarbon (BATH) assays, as well as for hydrocarbon removal by spectrophotometry and gas chromatography with flame ionization detection (GC-FID). In biosurfactant assays, SHA showed significantly higher E24 and BATH values than the other isolates (P < 0.05; Table 3). By spectrophotometry and GC-FID, SHA and SWOC achieved the highest crude-oil removal after seven days (84.2% and 85.8%, respectively), and GC-FID confirmed degradation across C13-C32 n-alkanes.Molecular identification based on 16S rRNA sequencing revealed that isolate SHA belonged to Acinetobacter junii (Gram-negative) and isolate SWOC to Lysinibacillus boronitolerans (Gram-positive). Interestingly, co-cultivation of the two isolates resulted in reduced degradation efficiency (55%), indicating an antagonistic interaction between them. These findings suggest that both isolates possess strong individual potential for the bioremediation of oil-contaminated soils, and further studies are warranted to investigate the mechanistic basis of antagonism and to validate their performance under field conditions.