Construction Of Root-colonized Degrading-bacterial Biofilm And Its Inhibition Effect On Accumulation Of Phenanthrene In Wheat

In recent years,the pollution of polycyclic aromatic hydrocarbons（PAHs）,a persistent organic pollutant,is getting worse and worse in Chinese cultivated land.PAHs can be uptake and accumulated by plants,posing a huge threat to human health and the ecosystem through food-chain bio-accumulation.Microorganism has a definite function of degradation of organic pollutants,and is the most valuable and promising subjects in the field of bioremediation.On the basis of the phenomenon that most microorganism exists in the form of biofilm in the nature environment,which can improve their biological functions and resistance,this paper build a exogenous biodegradable bacterial biofilms in order to enhance the degradation function of degrading bacteria and to prevent the pollutants transfer into plants,to achieve a good and continuous resistance control effect lastly.In this paper,phenanthrene represents the PAHs,the phenanthrene-degrading bacteria JM2 obtained from activated sludge were chosen as the experimental materials.Firstly,the toxicity effect of phenanthrene on wheat was studied.Secondly,the biofilm of phenanthrene-degrading bacteria on root surface was constructed by root soaking and the morphological structure was detected.Finally,the effect of the biofilm on the accumulation of phenanthrene and the growth of wheat was investigated.The main results are as follows:（1）With phenanthrene concentration increasing,the length of root and shoot,the biomass of wheat reduced gradually,the accumulation of phenanthrene,the activity of SOD/POD,and the content of chlorophyll increased at the early stage and then decreased,and peaked at 250 mg·L^-1.（2）The phenanthrene-degrading bacteria JM2 was labeled with GFP via triparental conjugation.Wheat roots were immersed in a suspension of strain JM2-gfp,after incubated 4days,the biofilm was mature.The results of SEM proved that bacteria were attached to root epidermal cells by a fibrillar-like material secreted by itself,in addition,the root with abundant exudates and stable such as root hairs and maturation zone,elongation zone,were benefit to the formation of biofilm.What’s more,biofilm on wheat roots can be maintained in a good status for at last 15 days,and the phenanthrene-degrading bacteria in biofilm can colonizated into root and stem.（3）According to hydroponic experiments,the biofilm of phenanthrene-degrading bacteria on root surface prevented the accumulation of phenanthrene by wheat,was lower71.96%and 89.01%than control.It can also decrease phenanthrene translocation from the roots to the shoots,the TF decreased by 61.77%.What’s more,the biofilm promoted the growth of wheat and improved the activity of POD,SOD and the content of chlorophyll in wheat.Based on above results,it can be determined that phenanthrene-degrading bacterial biofilm on root surface can prevent the accumulation of phenanthrene in wheat,avoid the risk of plant contaminant,which is of great significant to realize the production of safe agricultural products in polluted areas and the bio-remediation of contaminated farmland soil.It also provides an effective model system for the study of plant-microbial interaction.