Microbial degradation mechanisms of surface petroleum contaminated seawater in a typical oil trading port

Petroleum hydrocarbons are significant new persistent organic pollutants for marine oil spill risk areas. Oil trading ports, in turn, have become major bearers of the risk of offshore oil pollution. However, studies on the molecular mechanisms of microbial degradation of petroleum pollutants by natural seawater are limited. Here, an in situ microcosm study was conducted. Combined with metagenomics, differences in metabolic pathways , in the gene abundances of total petroleum hydrocarbons (TPH) are revealed under different conditions. About 88% degradation of TPH was shown after 3 weeks of treatment. The positive responders to TPH were concen-trated in the genera Cycloclasticus, Marivita and Sulfitobacter of the orders Rhodobacterales and Thiotrichales. The genera Marivita, Roseobacter, Lentibacter and Glaciecola were key degradation species when mixing dispersants with oil , all of the above are from the Proteobacteria phylum. The analysis showed that the biodegradability of aromatic compounds, polycyclic aromatic hydrocarbon and dioxin were enhanced after the oil spill, and genes with higher abundances of bphAa, bsdC, nahB, doxE and mhpD were found, but the photosynthesis-related mechanism was inhibited. The dispersant treatment effectively stimulated the microbial degradation of TPH and then accelerated the succession of microbial communities. Meanwhile, functions such as bacterial chemo-taxis and carbon metabolism (cheA, fadeJ and fadE) were better developed, but the degradation of persistent organic pollutants such as polycyclic aromatic hydrocarbons was weakened. Our study provides insights into the metabolic pathways and specific functional genes for oil degradation by marine microorganisms and will help improve the application and practice of bioremediation.

Automated summary

Petroleum hydrocarbons are significant new persistent organic pollutants for marine oil spill risk areas. Oil trading ports have become major bearers of the risk of offshore oil pollution. However, studies on the molecular mechanisms of microbial degradation of petroleum pollutants by natural seawater are limited. In this study, an in situ microcosm study was conducted, revealing differences in metabolic pathways and gene abundances of total petroleum hydrocarbons (TPH) under different conditions. The degradation of TPH was shown to be 88% after 3 weeks of treatment. Various bacterial genera, such as Cycloclasticus, Marivita, and Sulfitobacter, were identified as positive responders to TPH. The use of dispersants with oil enhanced the degradation of TPH, with certain bacterial species from the Proteobacteria phylum playing key roles. Additionally, the study found that the biodegradability of aromatic compounds and polycyclic aromatic hydrocarbons was enhanced after the oil spill, while the photosynthesis-related mechanism was inhibited. The dispersant treatment stimulated microbial degradation of TPH and promoted the succession of microbial communities. The study provides insights into the metabolic pathways and functional genes for oil degradation by marine microorganisms, which will contribute to the improvement of bioremediation applications and practices.