Biosurfactant-nonionic mixed micelles enhance heavy crude oil bioremediation: interfacial synergy and multilevel microbial responses.

To address the water-oil-cell interfacial mass-transfer barrier limiting microbial degradation of heavy crude oil, this study evaluated a biosurfactant-nonionic mixed-micelle strategy that integrates interfacial performance with microbial compatibility. Four binary surfactant systems were screened using the petroleum hydrocarbon-degrading consortium B10. Among them, the rhamnolipid/Triton X-100 formulation, designated RT, showed the best overall balance of mixed-micelle synergy, crude-oil solubilization, microbial growth compatibility, and apparent hydrocarbon attenuation. After 7 d, RT achieved an apparent attenuation efficiency of 60.0%, compared with 21.9% in the surfactant-free B10 control, with the largest increases observed for the C16-C22 and C23-C32 fractions. RT treatment was accompanied by increased protein-like extracellular polymeric substance (EPS) content, changes in FTIR and fluorescence characteristics, a more negative zeta potential, and greater apparent cell-surface hydrophobicity. Metatranscriptomic analysis further revealed higher transcript abundance of genes associated with motility and chemotaxis, membrane transport, fatty acid metabolism, and the tricarboxylic acid cycle. Together, these multidimensional observations support a proposed mechanism model in which mixed-micelle interfacial regulation is associated with EPS compositional responses, cell-surface property changes, and consortium-level transcriptional adjustments, rather than solubilization alone.