Biodegradation Of Di-n-butyl Phthalate And Dynamics Analysis Of The Key Bacterial Community In Soils

Phthalic acid esters (PAEs) are a class of refractory organic compounds, which could disturb the endocrine systerm of human and animals. PAEs have been listed as priority pollutants and endocrine disrupting compounds by many countries. Recently, due to the widely use, DBP have been liberated and detected in various environments including soils, rivers, lake, sediment of sea, drinking water, refuse dump and some food. The available literatures suggest that the routs of environmental degradation of PAEs are hydrolyze, photodegradation and biodegradation, microorganisms are responsible for the complete destruction of DBP in the environment. And lots of DBP degrading-bacteria were isolated from many kinds of environments.In this paper, four bacteria stains with DBP-degrading abilities were successfully isolated from sediment samples collected from four different sites. Based on morphological, physio-biochemical characteristics and homology identification of 16S rDNA sequence, the four strains (JDC2, JDC13, JDC26, JDC33) were identified as Gordonia sp. In addition, About 890 bp 3,4-phthalate dioxygenase gene were successfully amplified from JDC2, JDC13, JDC26, JDC33 with a pair of degenerate primers designed. And it was the first time that 3,4-phthalate dioxygenase gene were successfully amplified from the genus Gordonia. The sequences of the 3,4-phthalate dioxygenase gene from the four isolates in this study were highly homologous to each other. However, the difference is much more obvious compared with the phthalate dioxygenase gene from other genera.The optimal degrading conditions of DBP were tested and the result indicated that the optimal growth conditions of the four bacteria strains were 30℃, pH 7.0 and the agitation 175-250 r/min. the degradation capability of the foue isolates was determined by HPLC using DBP as test substrate under the optimal conditions. As a result, JDC2 degrade more than 96% of the 400 mg-L"1 DBP after 18 h. JDC13 and JDC26 degraded more than 98% of the 400 mg/L DBP after 30 h and 48 h, respectively. However, JDC33 only degraded 78% of the 400 mg/L DBP after 48 h. The biodegradation dynamics of the four strains fit well with first order kinetic reactions. And half-life of the strains JDC2, JDC13, JDC26, JDC33 were found to be 9.24 h,9.89 h,27.61 h,31.12 h, respectively. In addition, The results of degrading substrate range tests showed that the PAEs with shorter alkyl-chain were more easily ulitized than the longer alkyl-chains. JDC2 and JDC13 grew well in the PAEs medium than JDC26 and JDC33, especially in the PAEs with longer alkyl-chains.Bioaugmentation, the addition of microorganisms to enhance a specific biological activity, has been practiced intentionally for years in a number of areas. An experiment was conducted in lab by adding DBP soil with DBP alone and DBP plus DBP degrader JDC13. We studied biodegradation of DBP in soil, effect of the inoculant JDC13 on soil bacterial population. The DBP remained in soil was determined by HPLC. In the sample, which was added DBP alone, the DBP was completely degraded after 14 days. And in the sample, which was added DBP and JDC13, the DBP in soil was absolutely degraded after 9 days. It is clear that JDC13 can enhance the biodegradation of DBP in soil. The detection of soil bacterial counts indicated that DBP can inhibit the growth of local soil bacteria, but inoculation with JDC13 could reduce the negative effect of DBP on local soil bacteria.Changes of the bacterial community in the process of soils DBP degradation were monitored using PCR-DGGE. It is obvious that DBP alone and DBP plus JDC13 substantially affected the structure of bacterial community in the soil. Because adding DBP to the soils can enrich the bacteria which can use the DBP as the carbon resource, JDC13, Actinobacteria and Betaproteobacteria became the dominant bacteria in the DBP-contaminated soil. And most of them were homologous to the PAEs degrader.