Integration of top-down rhizospheric selection and bottom-up consortium engineering enhances mechanistic biodegradation of crude oil hydrocarbons and soil recovery.

Effective remediation of crude oil-contaminated soils enriched in recalcitrant polycyclic aromatic hydrocarbons (PAHs) requires strategies that couple microbial degradative capacity with ecological compatibility. This study evaluated an ex situ rhizoremediation system integrating Crotalaria pallida with a trait-selected hydrocarbon-degrading bacterial consortium and a biosurfactant amendment, using a combination of bottom-up functional selection and top-down rhizosphere filtering. After 90 days, consortium-amended treatments achieved up to 98.3% PAH and 94.7% total petroleum hydrocarbon (TPH) removal, accompanied by a significant decrease in PAH-associated ecological risk. GC-MS profiles showed a reduction of aliphatic and aromatic hydrocarbons and the presence of oxidized transformation products, suggesting transformation of the residual hydrocarbon fraction. Hydrocarbon attenuation was accompanied by increased soil enzymatic activities and treatment-associated restructuring of the rhizosphere bacterial community. Amplicon-based bacterial community profiling revealed shifts in key bacterial taxa, while PICRUSt analysis indicated treatment-associated differences in predicted functional pathways related to xenobiotic and hydrocarbon metabolism. Together, the chemical, biochemical, and microbial responses demonstrate that integrating C. pallida with a trait-selected bacterial consortium, supplemented with biosurfactants, can stimulate hydrocarbon attenuation while supporting the biological recovery of crude oil-contaminated soil. These findings provide an integrated rhizoremediation framework linking contaminant removal to microbial community restructuring, predicted functional potential, and a reduction in PAH-associated ecological risk.