Abstract
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.