Screening Of Phenanthrene Degrading Bacteria With Growth Promoting Characteristics And Their Participation In The Remediation Of Phenanthrene Contaminated Soil By Rape

With the development of industry and the emission of daily life,polycyclic aromatic hydrocarbons(PAHs)have become a kind of representative persistent organic pollutants widely existing in farmland soil environment.The use of agricultural land containing PAHs not only affects the yield and quality of crops,but also seriously acts on food safety and human health through the food chain.Using phytoremediation technology to repair PAHs contaminated soil safely and efficiently is a hot topic with research significance and development prospect,but the ability of plants to absorb,transport,accumulate and tolerate PAHs is the key to restrict the phytoremediation efficiency of contaminated soil.The purpose of this study is to explore the effect and mechanism of phenanthrene(PHE)degrading bacteria with growth promoting characteristics on improving the tolerance of rape in polluted soil and repairing soil pollutants at the same time through plant-microbial joint remediation technology.The main research results are as follows:(1)12 PHE degrading bacteria with growth promoting characteristics were isolated from the roots and rhizosphere of Festuca elata growing in oil polluted soil.Through the determination of growth promoting indexes,6 strains of DLY5,DLY7,DLN2,DLN3,DLN4 and DLN5 were preliminarily screened.It was verified that the PHE degradation rates of the six strains were all more than 75%.By 16 S rDNA sequence analysis,the six strains were identified as Bacillus,Paraclostridium,Stenotrophomonas,Achromobacter,Pseudomonas and Serratia.(2)The effects of six strains on seed germination and plant growth of rape under PHE stress were studied by pot experiment.These six strains significantly promoted the germination of rape seeds and significantly enhanced the growth indexes of seedlings.After long-term observation,it was found that the growth condition of rape treated with strain DLN5 was the best.The inoculation of DLN5 improved the root activity of rape under PHE stress,and greatly promoted the photosynthetic efficiency.In further determination,it was also found that the growth promoting and degrading bacteria increased the contents of osmotic pressure regulating substances and GSH in vivo.The activities of alkaline phosphatase and catalase in rhizosphere soil of inoculation group were remarkably increased,and the content of PHE in soil decreased by 71.44%.(3)QPCR and high-throughput sequencing showed that Serratia sp.DLN5 could colonize and stably exist in the root of rape.The colonization of this functional endophytic bacterium had no significant effect on the microbial diversity of rape rhizosphere soil,but significantly changed the bacterial community structure.After inoculation with strain DLN5,the relative abundance of Sphingomonas,Nitrospira,Burkholderiaceae and OLB14 in rhizosphere soil was significantly increased,and most of the biomarkers with rich differences belonged to Methylophilase,OLB14,Burkholderiaceae and Flavobacterium.The above dominant microorganisms and biomarkers were previously found to degrade petroleum hydrocarbons or aromatic hydrocarbons in soil.Therefore,the change of community structure caused by DLN5 inoculation is considered to be conducive to enhance the repair and degradation ability of rhizosphere microorganisms to PHE and the growth promotion ability to plants.