Effects Of Polycyclic Aromatic Hydrocarbons (PAHs) Pollution On Microbial Community Composition In Farmland

In recent years,the contents of organic pollutants such as polycyclic aromatic hydrocarbons(PAHs)are increasing in farmland.They are absorbed and transported into food chains,then seriously threatened human health.Studies have shown that PAHs pollution can reduce microbial diversity of soils,but they can also be used as a carbon source by some special microorganisms,stimulating microbial growth,leading to form new microbial community composition,and discovering dominant microorganisms that effectively degrade organic pollutants.This has high research value in bioremediation.This work collected the PAHs contaminate farmland from environment,and compared the bacterial community composition differences between crop rhizosphere and non-rhizosphere soils.Moreover,the abundance of PAH-ring hydroxylating dioxygenase(PAH-RHD?)genes was analyzed to further explore the dominant microbial resources.Pseudomonas sp.JM2-gfp,which has been isolated from the laboratory,was used the dipping root culture and root box test for investigating the disturbance of indigenous microbial communities in the soil contaminated by phenanthrene by the addition of exogenous functional bacteria,and providing a scientific basis for bioremediation of organic contaminated farmland.The main findings are as follows:(1)The effects of soil microbial activity in farmland stressed by PAHs were discussed.Soil samples near the oil wells in Liaoning Province were collected.The results showed content of 16 PAHs was 38884 ?g/kg,soil was seriously polluted by PAHs.The microbial activity indicators of soil include microbial biochar,culturable bacteria number and microbial respiration intensity,the results showed the microbial activity of the contaminated soil was lower than that of the nearby uncontaminated soil,and the microbial activity of rhizosphere soil is higher than that of non-rhizosphere soil in polluted areas.(2)Using 16 S rDNA high-throughput sequencing and real-time fluorescent quantitative PCR(qPCR)to study the differences of bacterial community composition between rhizosphere soil and non-rhizosphere soil in the farmland polluted by PAHs.Sequencing results show that the bacterial community diversity index in rhizosphere soil was significantly higher than that in non-rhizosphere soil.What's more,PAHs contaminated farmland had rich dominant microbial resources,including Burkholderiaceae,Geobacter and Sphingomonas,Sulfuricurvum and Thiobacillus as well.Compared with non-rhizosphere soil,the relative abundance of Geobacter and Thiobacillus in the rhizosphere soil were increased.The consequence of qPCR showed the copy number of cyclohydroxylation dioxygenase gene in rhizosphere soil is significantly higher than that in non-rhizosphere soil.It was indicated that the Geobacter and Thiobacillus may have microbial resources for degrading PAHs.(3)The effects of the addition of phenanthrene-degrading bacteria on the rhizosphere microbial community of rice was analyzed.After 60 days of soil culture,JM2-gfp was able to colonize and survive on the root surface.After JM2-gfp colonization,the microbial diversity index of rhizosphere soil was slightly lower than that of rhizosphere soil without colonization,and the proportion of proteobacteria was greatly increased.The functional bacteria including Rhizobium,Sphingomonas and Neosphingosine,whose relative abundance were significantly increased.