The Impact Of Biosurfactants And Chemical Dispersants On Oil-degrading Microorganisms

Oil is an important energy source for the current social development.However,with the rapid exploitation of offshore oil and the rapid development of shipping,marine oil spills occur frequently.Coastal waters have gradually become a high-risk area for oil spill.Application of chemical dispersants to oil spills in the marine environment is a common practice to disperse oil into the water column and stimulate oil biodegradation by increasing its bioavailability to indigenous bacteria capable of naturally metabolizing hydrocarbons.However,their efficacy is under debate with studies reporting both suppression and stimulation of microbial oil degradation.In addition,limited studies have been done on the impact of dispersant on marine oil microbial biodegradation.In this study,we simulated marine oil spill conditions for laboratory incubation experiments.Seawater of Sanya Bay in China was used to carry out the experiment.In this experiment,Miseq high-throughput sequencing technology,real-time quantitative PCR,Gas Chromatography–Mass Spectrometry?GC-MS?,and radioisotope tracer technology were used to explore the effects of biosurfactant?rhamnolipid?,Chinese chemical dispersant Jiefeite?JFT?,Slickgone NS and Corexit 9500 on the oil degradation rate and oil-degrading microorganisms.The main results are as follows.1.Neptuniibacter,Planctomyces,Thalassobius,and C1-B045 were the dominant indigenous oil-degrading bacteria in the seawater of Sanya Bay.2.JFT promoted the degradation of petroleum components?total alkanes and total PAHs?Polycyclic Aromatic Hydrocarbons??.³H-Leucine/¹⁴C-hexadecane/napthalene based radioactive tracer experiments revealed that JFT promoted the activities of total microbial communities and oil-degrading microorganisms.The key oil-degrading bacteria has been changed to Oleiphilus,Oleibacter,Planctomyces,Pseudohongiella,Marinobacter,Formosa,and C1-B045 by the addition of JFT.The significant increase of alkB gene copy number was observed by the addition of JFT?P<0.05?,whereas no significant effect of JFT was observed on the abundance of the phnAc gene.3.Slickgone NS showed no impact on the degradation rate of oil.The radioisotope traces-based experiment revealed that the addition of Slickgone NS had no significant effect on the activity of oil-degrading microorganisms.Neptuniibacter,Spongiibacter,Thalassobius,Arcobacter,Planctomyces,and C1-B045 were the dominant oil-degrading microorganism.The decreasing abundance of the alkB gene was found by the addition of Slickgone NS,but had no significant effect on the copy number of the phnAc gene.4.The systematic comparisons of the impacts of biosurfactants rhamnolipid and chemical dispersants Corexit 9500 on microbial community and oil biodegradation was performed Rhamnolipid stimulated the degradation rate of oil components,while Corexit9500 inhibited the oil degradation rate.The radioisotope traces-based experiment revealed that rhamnolipid stimulated the activity of oil-degrading bacteria,while Corexit 9500 inhibited.Pseudomonas,Formosa,Alcanivorax,and Pseudohongiella were the dominant oil-degrading bacteria when rhamnolipid was present.Neptuniibacter,Planctomyces,Pseudohongiella,and C1-B045 were the main oil-degrading bacteria by the addition of Corexit 9500.Rhamnolipid significantly increased the abundance of the alkB gene,while Corexit 9500 had no significant effect on the abundance of alkB gene.5.The addition of nutrients promoted the activity of total microorganisms and oil-degrading microorganisms.And it was found that the abundance of 16S rRNA and alkB genes increased by the addition of nutrients.In summary,results showed that JFT and biosurfactants stimulated the oil microibal degradation in Sanya Bay.Corexit 9500 inhibited the oil microbial degradation,while Slickgone NS showed no significant effect on the oil microbial degradation.JFT and rhamnolipid both promoted the metabolic activity of oil-degrading microorganisms,and Slickgone NS and Corexit 9500 inhibited the activity of oil-degrading bacteria.Rhamnolipids and different chemical dispersants resulted in the different patterns of oil-degrading bacteria.The results of this study will help to deepen the understanding of the environmental effects of biosurfactants and various dispersants on the ecological functions of marine microorganisms,and provide a scientific theoretical basis for the use of dispersants in future oil spill accidents.The results also provide important ecological value and practical guiding significance.