Studies On Degradation Of DBP By Sphingomonas Sp.XJ1

Phthalate acid esters(PAEs)are an important class of organic chemicals that mainly used as plasticizers in plastics.Due to their large production and widespread use,PAEs pollution has become an increasingly serious environmental problem and has aroused particular attention from countries in the world.Recent researches show that PAEs in the environment have a quiet slow rate for both hydrolysis and photolysis,and biodegradation of PAEs is considered to be an important route for their elimination from the environment.In this paper,DBP was used as the sole carbon and energy source to domesticate and screen the microbes from Xiangjiang River sediment. DBP degradation capability was measured by high performance liquid chromatography(HPLC),diversity of degradable substrates was also tested.In the end,a predominated bacterium,designated as strain XJ1, was isolated from Xiangjiang River sediment.The strain XJ1 was identified as Sphingomonas sp.based on 16S rDNA sequence analysis, (G+C)mol%and its morphological and physiological characteristics. The optimum conditions for DBP degradation by strain XJ1 were initial pH 7.0,35℃and agitation rate being 150 rpm.In 40h,DBP at the initial concentration of 100 mg/L was degraded completely under the optimum conditions,which showed that DBP could be degraded effectively by strain XJ1.Diversity of degradable substrates showed that phthalate esters such as dimethyl phthalate,diethyl phthalate,etc.which showed that the strain XJ1 had special application potential on bioremediation for phthalate esters contaminated site。According to the literatures on the aerobic biodegradation pathway of DBP,the DBP metabolites were detected by HPLC-UV and were identified as mono-butyl phthalate(MBP),phthalate acid(PA)and protocatechuate acid(PCA)by the retention time of the standard compounds.In the end,the DBP degradation by Sphingomonas sp.XJ1 was proposed:DBP was firstly hydrolyzed to MBP and subsequent PA, then was further metabolized to PCA and finally to produce CO₂ and H₂O. PAEs have low water solubility and high octanol/water partition coefficients,its behavior in the soil is mainly on the absorption in the soil particles,and mass transfer from the solid to the liquid phase may be the rate-limiting step in biodegradation of PAEs.Surfactant addition may help the PAEs transfer from solid phase(such as soil particles)to liquid phase,which is conducive to microbial degradation.In order to further clarify the effect of surfactant on the biodegradation of PAEs,the interaction among DBP,surfactant and bacterium was investigated.The result showed that Tween 80 could increase the apparent solubility of DBP in the water,and the apparent solubility of DBP in the water is linear to the Tween 80 concentration from 1×CMC to 10×CMC;Tween 80 was nontoxic to the tested bacterium,had no apparent role in promoting DBP biodegradation and didn't inhibit DBP biodegradation;Tween 80 could enhance the cell surface hydrophobicity(CSH)of the bacterium and the bacterium had its CSH somewhat due to its special chemical constitution of cell membrane;Tween 80 was not ready biodegradation and much attention should be paid to its applification before bioremediation.