Mechanisms Underlying Efficient n-Eicosane Degradation and Physiological Adaptation in Rhodococcus erythropolis KB1

Low temperature limits microbial remediation of petroleum hydrocarbon-contaminated environments, yet the physiological basis for long-chain alkane degradation under cold stress remains insufficiently understood. In this study, Rhodococcus erythropolis KB1 was cultured with n-eicosane as the sole carbon source at 4°C, 16°C, and 30°C for 5, 10, and 15 days. Degradation performance, growth-associated traits, surface tension, membrane permeability, redox-energy metabolism, key enzyme activities, and putative GC-MS signals were evaluated. KB1 showed the highest n-eicosane degradation efficiency at 30°C, reaching 86.84 ± 0.21% by Day 15, accompanied by enhanced biomass accumulation, protein content, cytochrome P450 monooxygenase (CYP450) activity, adenosine triphosphate (ATP) and nicotinamide adenine dinucleotide phosphate (NADPH) contents, and Na⁺-K⁺-ATPase and Ca²⁺-Mg²⁺-ATPase activities. Notably, KB1 retained substantial low-temperature degradation capacity, achieving 60.13 ± 0.44% degradation at 4°C by Day 15. Correlation analysis indicated that degradation efficiency was associated with membrane permeability, reducing-power supply, ion-transport activity, biomass accumulation, and interfacial regulation rather than a single enzymatic response. Gas chromatography-mass spectrometry (GC-MS) analysis detected 23 putative compounds, including shorter-chain alkane-related signals, fatty alcohols, and fatty acid methyl esters, supporting a pathway involving terminal oxidation, β-oxidation, and downstream tricarboxylic acid (TCA)-cycle-related metabolism. Overall, R. erythropolis KB1 coordinates membrane-interface remodeling, redox-energy coupling, ion transport, and oxidative transformation to sustain n-eicosane degradation across temperature gradients. These findings identify KB1 as a promising cold-adapted microbial resource for petroleum hydrocarbon bioremediation.