Rhamnolipid-mediated crude oil recovery and biodegradation using Citrobacter amalonaticus: Implications for sustainable soil remediation

Crude oil contamination remains a major environmental challenge, necessitating sustainable and efficient remediation strategies. In this study, the synergistic potential of a biosurfactant and its producing strain, Citrobacter amalonaticus TES I, was investigated for crude oil recovery and biodegradation in contaminated soil systems. The rhamnolipid biosurfactant, owing to its superior surface-active properties, facilitated hydrocarbon emulsification and increased the bioavailability of petroleum fractions, thereby improving microbial access to complex hydrocarbons. The optimized biosurfactant reduced surface tension from 72 to 41.41 mN/m and exhibited a critical micelle concentration (CMC) of 60 mg/L. Laboratory-scale biosurfactant-assisted oil recovery achieved 75.90% crude oil recovery. Furthermore, treatment with C. amalonaticus TES I resulted in an 88.7% reduction in recoverable petroleum hydrocarbons after 30 days, as determined by gravimetric analysis, while GC-MS analysis indicated changes in the degradation and transformation of aliphatic and aromatic fractions following biosurfactant treatment. Mechanistic insights obtained from FTIR, NMR, dynamic light scattering (DLS), zeta potential analysis, FESEM-EDX and GC-MS collectively demonstrated enhanced hydrocarbon mobilization and transformation of petroleum fractions following biosurfactant treatment. The reduction in interfacial tension mediated by rhamnolipid played a critical role in promoting hydrocarbon uptake and accelerating biodegradation pathways. The study highlights the applicability of biosurfactant-assisted bioremediation as a sustainable and eco-friendly approach for restoration of petroleum-contaminated soils. The findings contribute to the advancement of integrated biotechnological solutions for environmental cleanup and circular bioeconomy-based remediation strategies.