Low Temperature Biodegradation of Heavy Oil by Pseudomonas Strains Isolated from Oil- Contaminated Sites and Activated Sludge

Low temperatures increase the viscosity of heavy oil and limit the solubility of short-chain alkanes, which increases their toxicity to microorganisms and delays biodegradation. This study aimed to isolate efficient heavy oil-degrading bacteria from contaminated soil and sewage sludge to evaluate their potential for bioremediation under cold climate conditions. Using enrichment culture with heavy oil as the sole carbon source, two potent strains (designated C1 and C2) were isolated from the Japanese soil, and a third strain (C3) was isolated from the Korean sludge. All three strains were identified as Pseudomonas aeruginosa via 16S rDNA sequencing. Residual oil was estimated using Gas chromatography analysis. At 30°C, C1, C2, and C3 showed 57%, 51%, and 33% after 7 days, respectively. At 15°C, degradation was delayed by a lag phase, suggesting a temperature-dependent metabolic activation. At 10°C, C3 displayed negligible activity, whereas C1 and C2 degraded 49% and 12% in two weeks. Notably, at 5°C, no activity was observed in 7 days. However, 35% degradation was observed by C1 and C2 after 98 days. The strains C1 and C2 also showed 60% and 70% heavy oil biodegradation in artificially contaminated soil at 5°C. In conclusion, these Pseudomonas strains, especially C1 and C2 demonstrated the ability to degrade heavy oil in low-temperature environments and can contribute to environmental sustainability.