Effects Of Oil Spill Dispersants On Oil-degrading Microorganisms In Coastal Wetland Sediments

In recent years,coastal wetlands have suffered from serious oil pollution due to frequent oil extraction and transportation activities,posing a great threat to ecosystems and human health.Oil spill dispersants are one of the important measures to deal with oil pollution in an international emergency because of their ability to improve the solubility and bioavailability of the oil.However,there are limited studies on the effect of oil spill dispersant application on the degradation process of oil in coastal wetland sediments and its overall effect on microorganisms.To this end,this study conducted oil pollution simulation experiments for coastal wetland sediments in Ningbo,China,using high-throughput sequencing technology,fluorescence quantitative PCR,and gas chromatography-flame ionization detector GC-FID to investigate the effects of three oil spill dispersants,chemical dispersant JFT approved by the China Oceanic Administration,chemical dispersant Slickgone NS and biosurfactant Rhamnolipid（Rha）in Europe and America,on the sediment aerobic and oil degradation rates and oil degrading microorganisms under anaerobic conditions;in addition,DNA-based stable isotope probing（DNA-SIP）combined with high-throughput sequencing technology was used in this study to reveal the effects of different oil spill dispersants on the degradation of polycyclic aromatic hydrocarbons（PAHs）in sediments and their key active degradation microbial populations were investigated.The main studies and results of the paper are as follows:1.Under aerobic culture conditions:1)Addition of JFT,Slickgone NS,and Rha all significantly promoted microbial degradation of petroleum（P<0.05）.2)Addition of dispersants significantly affected the abundance of functional genes phn Ac and alk B for petroleum-degradation.The addition of JFT and Slickgone NS resulted in a significant increase in phn Ac gene copy number（P<0.05）,while there was no significant increase in alk B gene copy number;in contrast,the addition of Rha resulted in a significant increase in alk B gene copy number（P<0.05）and no significant change in phn Ac gene copy number.3)In terms of changes in microbial community structure,the coastal wetland The dominant natural aerobic oil-degrading bacteria in the sediments were Sulfurovum and Woeseia,while Syntrophotalea and Sulfurovum together became the dominant oil-degrading bacteria in the treatment with JFT and Slickgone NS.In addition,JFT specifically promoted the increase of the petroleum-degrading bacteria Marinobacter,and Slickgone NS promoted the increase of the petroleum-degrading bacteria Sphingomonadaceae.Sulfurovum,Pseudomonas,and Lachnospirales acted as the dominant petroleum degrading group in the treatment with the addition of Rha.4)The functional gene prediction results showed that the proportional increase in the abundance of functional genes involved in petroleum degradation was ranked as Rha>JFT>Slickgone NS after the addition of different dispersants.2.Under anaerobic incubation conditions:1)The addition of JFT significantly promoted the microbial degradation of petroleum（P<0.05）,while Slickgone NS and Rha did not significantly promote the degradation of petroleum.2)From the changes in microbial community structure,the dominant natural anaerobic petroleum degrading bacteria in the coastal wetland sediments were Desulfobulbaceae and Anaerolineaceae,and the addition of JFT and Slickgone NS specifically promoted the increase of the petroleum degrading bacteria Syntrophotalea,and the addition of Rha specifically promoted the increase of the petroleum degrading bacteria Marinifilum.3)The predicted results of functional genes showed that the addition of different dispersants increased the abundance of functional genes involved in petroleum degradation.The proportional increase in abundance of Rha≈JFT>Slickgone NS was ranked as follows.3.Using benzo[a]anthracene as a representative PAHs,the effects of adding dispersants on the degradation population of active PAHs in sediments were revealed as follows:1)Both JFT and Rha additions significantly promoted the aerobic microbial degradation rate of benzo[a]anthracene（p<0.05）.2)Ultrahigh-speed density gradient centrifugation analysis of ¹³C-DNA revealed that in the treatment with only benzo[a]anthracene addition,the Mucilaginibacter dominated the aerobic PAHs degradation process in this coastal wetland sediment;with the addition of JFT,PAHs degrading bacteria became dominated by Leucobacter;with the addition of Rha,PAHs degrading bacteria were dominated by Xanthobacteraceae.3)The functional gene prediction results showed that the addition of JFT treatment resulted in toluene（3）The predicted functional genes showed that the expression of functional genes of toluene degradation,naphthalene degradation,styrene degradation and PAHs degradation pathways increased significantly after the addition of JFT,and the expression of functional genes of nitrotoluene degradation,and PAHs degradation pathways increased significantly after the addition of Rha.In summary,the petroleum degradation processes in sediments of coastal wetland ecosystems under aerobic and anaerobic conditions were driven by different petroleum-degrading microbial populations.The addition of chemical dispersants and biosurfactants had significant effects on the rate of petroleum degradation and the differentiation of microbial populations.The results of this study are of guiding significance for understanding the environmental effects of different dispersants on the microbial ecological functions of coastal wetland sediments,and provide a scientific and theoretical basis for the use of dispersants in oil spills,which has important ecological and practical values.