Environmental contamination from heavy oil is a worldwide problem. In this study, a heavy oil degrading bacterial consortium DL-1314 composed of Bacillus sp. DL-13, Brevibacillus sp. DL-1 and Acinetobacter sp. DL-34 was constructed. The constituents were all biosurfactant-producing bacteria and heavy oil-degrading bacteria. Bench-scale experiments were used to investigate the performance of the bacterial consortium in degrading heavy oil. The bacterial consortium could quickly start up the heavy oil biodegradation and degrade 60.75% of heavy oil in 8 days. Gas chromatography-mass spectrometry (GC-MS) analysis evidenced that the bacterial consortium could degrade 66.32% of saturated hydrocarbons and 63.16% of aromatic hydrocarbons, especially C15-C35 n-alkanes and 2- ring-5-ring PAHs. Analysis of the dynamic changes in the consortium DL-1314 revealed that Bacillus sp. DL-13 played a major role in the formation of surfactants in the early stage of biodegradation, Brevibacillus sp. DL-1 degraded light hydrocarbons in heavy oil, and Bacillus sp. DL-13 and Acinetobacter sp. DL-34 degraded bio-refractory hydrocarbons in heavy oil by synergistic metabolism. In-depth characterization composition of the heavy oil and the microbial consortium revealed chemical and degradation diversity, providing a more comprehensive and accurate understanding of the biodegradation process.

High-efficiency bioremediation technology for heavy oil pollution has been a popular research topic in recent years. Laccase is very promising for the remediation of heavy oil pollution because it can not only convert bio-refractory hydrocarbons into less toxic or completely harmless compounds, but also accelerate the biodegradation efficiency of heavy oil. However, there are few reports on the use of laccase to enhance the biodegradation of heavy oil. In this study, we investigated the effect of laccase on the bacterial consortia degradation of heavy oil. The degradation efficiencies of bacterial consortia and the laccase-bacterial consortia were 60.6 ± 0.1% and 68.2 ± 0.6%, respectively, and the corresponding heavy oil degradation rate constants were 0.112 day⁻¹ and 0.198 day⁻¹, respectively. The addition of laccase increased the heavy oil biodegradation efficiency (p < 0.05) and biodegradation rate of the bacterial consortia. Moreover, gas chromatography–mass spectrometry analysis showed that the biodegradation efficiencies of the laccase-bacterial consortia for saturated hydrocarbons and aromatic hydrocarbons were 82.5 ± 0.7% and 76.2 ± 0.9%, respectively, which were 16.0 ± 0.3% and 13.0 ± 1.8% higher than those of the bacterial consortia, respectively. In addition, the degradation rate constants of the laccase-bacterial consortia for saturated hydrocarbons and aromatic hydrocarbons were 0.267 day⁻¹ and 0.226 day⁻¹, respectively, which were 1.07 and 1.15 times higher than those of the bacterial consortia, respectively. The degradation of C15 to C35 n-alkanes and 2 to 5-ring polycyclic aromatic hydrocarbons by laccase-bacterial consortia was higher than individual bacterial consortia. It is further seen that the addition of laccase significantly improved the biodegradation of long-chain n-alkanes of C22–C35 (p < 0.05). Overall, this study shows that the combination of laccase and bacterial consortia is an effective remediation technology for heavy oil pollution. Adding laccase can significantly improve the heavy oil biodegradation efficiency and biodegradation rate of the bacterial consortia.

Bioremediation of extra-heavy oil contaminated soil has become a hot research field. It is difficult for extra-heavy oil to be degraded by bacteria. In this study, strain C-1 was isolated from Venezuelan extra-heavy oil-contaminated soil. Morphological, physiological and phylogenetic analysis identified strain C-1 as Dietzia cercidiphylli. The strain could degrade 25.58 ± 0.48% of extra-heavy oil at an initial concentration of 100 mg L⁻¹ in 14 days with the degradation rate constant of 0.021 per day. GC-MS analysis demonstrated that the strain could effectively degrade medium (C13–C17) and longer (C44) length chain n-alkanes. This is the first report that the Dietzia strain can degrade extra-heavy oil, especially C44 n-alkanes. Dietzia cercidiphylli C-1 could be applied in extra-heavy oil contaminated soil bioremediation in the future.