Synergistic Bacterial Consortium Enables Rapid Engine Crude Oil Degradation Under Alkaline-Marine Stress

Petroleum hydrocarbon contamination under alkaline–marine conditions remains a critical environmental challenge due to reduced microbial activity and persistence of recalcitrant fractions. In this study, five biosurfactant-producing hydrocarbon-degrading bacterial strains (Ochrobactrum tritici, Achromobacter xylosoxidans, Rhizobium sp., Novosphingobium organovorum, and Sphingobium yanoikuyae) were evaluated individually and as a consortium for the degradation of 3% engine crude oil under simulated marine stress (pH 8.7, 3.5% NaCl, 30°C). GC–MS-based quantitative analysis revealed fraction-specific degradation: the consortium achieved near-complete removal of alkanes (99.63%) and cycloalkanes (99.54%) by day 20, and complete degradation of benzene, toluene, ethylbenzene, and xylene (BTEX) and polycyclic aromatic hydrocarbons by day 10. Time-resolved metabolite profiling identified key intermediates including fatty acids, catechol derivatives, and phthalic acid, indicating coordinated β-oxidation and aromatic ring-cleavage pathways. The consortium exhibited enhanced degradation kinetics (k = 0.124–0.280 day–1) and higher specific growth rate (µ = 0.103 day–1), demonstrating metabolic synergy. CFU-based population dynamics further confirmed cooperative interactions and functional specialization among strains. These findings provide mechanistic and quantitative insights into consortium-driven hydrocarbon biodegradation under alkaline–saline stress conditions.