Degradation Of Phthalic Acid Esters By A Novel Gordonia Sp.Strain YC-JH1

Phthalic acid esters(PAEs)used as plasticizer were constantly released into the environment with products for industry and life which caused severe threat to the ecological environment security and human health.High efficient degradation of PAEs residues in the environment has become the urgent needs of the current environmental protection and the research hot spot.Bioremediation is one of the important means of environmental governance,that is,screen and isolate high efficient degradation microorganisms and use them to degrade pollutants.In this study,a degradation bacterium YC-JH1 was isolated from oil polluted soil with the ability to convert PAEs to non-toxic phthalic acid(PA)and benzoic acid(BA)through its corresponding mono-PAEs.According to 16 s rDNA sequence alignment,microscope and transmission electron microscopy(SEM)observation,the strain was identified as a Gordonia bacterium.Effect of different environmental factors on DEHP degradation of YC-JH1 was detected,showing that YC-JH1 can maintain high degradation ability in a wide range of temperature(20~40 °C)and pH(6~12).The optimal condition is 35-40 °C,pH10 and no salt supplement.YC-JH1 showed a good tolerance to high concentration of DEHP to 2.5 mM(1000 mg/L)and a wide variety of PAEs.YC-JH1 could efficiently degrade PAEs with complex and long straight side chains and short side chains except DMP(Dimethyl phthalate)and showed higher degradation rate with longer side chains.Intermediates of DEHP degradation were analyzed by HPLC-QQQ and a presumable degradation pathway was subsequently speculated: the two ester bonds in DEHP were successively fractured by YC-JH1,the generated PA was then decarboxylatedlly converted to BA.Protein localization assay revealed that key enzymes responsible to break the first ester bond of PAEs were located in intracellular.No obvious massive esterase expression under the induction of substrate DEHP indicated that esterases might be constitutively expressed in YC-JH1.On the basis of a reported MEHP hydrolase gene sequence,a MEHP hydrolase gene in YC-JH1 was cloned and expressed in E.coli BL21 cells.A recombinant MEHP hydrolase was purified and functionally verified.