Enhanced Degradation Of DEP By An Efficient Diethyl Phthalate Degradation Bacterium Pseudomonas Sp.DNE-S1

Diethyl phthalate?DEP?,a kind of macromolecular ester organic substance,mainly used as a plasticizer to increase the plasticity of plastics and the strength of plastics.It was usually discharged into the environment from the manufacturing process.It was often detected at relatively high levels in soil,sediment and water.It had toxic and harmful effects on mammals and aquatic animals.It was listed as the environmental priority control pollutant and endocrine disrupting compound by the China Environmental Monitoring Center and the US Environmental Protection Agency.Biodegradation became the main way to remove DEP in the environment because of its rapid degradation efficiency,no secondary pollution,and green.A strain with high efficiency degradation of DEP was isolated from landfill soil and named DNE-S1.The colony morphology,physiological and biochemical,molecular biological identification,etc.were studied,and the optimal growth conditions,growth degradation kinetics and metabolic pathways were studied.After adding exogenous regulatory factors,the morphology,degradation ability and relative expression of related degradation genes were changed.Finally,the environmental application of strain DNE-S1 was preliminarily investigated by magnetic graphene oxide composites,and its application range and degradation ability were improved.The detailed research results were as follows:?1?By 16s-r RNA and Blast homology analysis,strain DNE-S1 was identified as Pseudomonas sp.and its NCBI accession number was MF803832.The DNE-S1 had slightly convex colony in the inorganic salt solid medium,which was slightly yellow with neat edges and opaque,and was a Gram-positive bacteria.Under the scanning electron microscope,the morphology of the strain was observed as a bacterium,which was 1.648 ?m long and 0.5 ?m wide.?2?Taking the growth of OD₆₀₀ of strain DNE-S1 as the target,the p H,temperature and DEP concentration were used as variables to carry out single factor test.Studies had shown that strains had the ability to grow under a wide range of acid and alkali conditions and had good tolerance to high concentrations of DEP.On the basis of this,a three-dimensional response surface was drawn,and the optimal growth conditions of strain DNE-S1 were found,p H 8.51 and 29.96?.?3?Under the optimal conditions p H 8.51 and 29.96?,the different DEP concentrations were investigated for strain DNE-S1.The strain DNE-S1 was found to follow the substrate inhibition model in terms of growth and degradation,and the DEP degradation rate of 500 mg L-1 was the highest,97.8%.At the same time,the metabolism was studied,and three degradation intermediates,namely ethyl phthalate?EMP?,dimethyl phthalate?DMP?and phthalic acid?PA?,were detected and a metabolic pathway for DEP degradation was proposed.?4?By adding four exogenous regulatory factors Cu2+,Zn2+,Mn2+ and Fe3+,in the presence of 100 ?g L-1 Fe3+ it was found that the degradation rate of strain DEP increased by 14.5% in 12 h.Cu2+,Zn2+,Mn2+ inhibited the degradation of the strain.The presence of exogenous regulatory factors changed the cell morphology,surface area and volume of DNE-S1.At the same time,it was found that Fe3+ promoted the degradation of DEP by DNE-S1,through the overexpression of gene phthalate dihydrogenate dehydrogenase?oph B?and phthalate dioxygenase ferredoxin reductase?oph A4?.?5?The prepared composite material GO@Fe3O4-CMC was characterized by Fourier Transform infrared spectroscopy,scanning electron microscopy and X-ray diffraction.The results showed that the surface of the composite had a large number of hydrophilic groups,which improved the dispersion of DEP in aqueous solution and the degradation ability of DNE-S1.DNE-S1 screened by the study had the ability to degrade DEP efficiently,and had a wide range of adaptation,providing a certain theoretical basis and technical support for microbial remediation technology.