Metabolites And Genes Of Enterobacter Sp. LY402 Related With Polychlorinated Biphenyls Biodegradation

Polychlorinated biphenyls (PCBs) are one of the important organic chlorinated pollutants in the environment due to the physical and chemical stability and recalcitrant to biodegradation. A strain LY402 which could efficiently degrade highly chlorinated and coplanar PCBs was isolated from soil contaminated and classified as Enterobacter sp.. In this study, the metabolites from polychlorinated biphenyls biodegradation by Enterobacter sp. LY402 are identified, and the PCBs-degrading genes are isolated. Experimental results are as follows:(1) Through GC-MS and GC-ECD analysis, chlorobenzoates are identified as metabolites of PCBs-degrading by Enterobacter sp. strain LY402. Single PCB congeners 2,2'- and 2,3-dichlorinated biphenyls are transformed to 2-chlorobenzoate and 2,3-dichlorobenzoate, respectively. PCBs mixture Aroclor 1242 is transformed to at least eight types of chlorobenzoates, including two types of monochlorobenzoates, four types of dichlorobenzoates and two types of unknown trichlorobenzoates.(2) The release of chloride in the course of 2,2'-dichlorobiphenyl degradation was observed by using the modified HNO₃-AgNO₃ method.(3) The degradation of seven types of mono-/di-chlorobenzoates (2μg/ml each) mixture by Enterobacter sp. LY402 shows that, the strain has the ability to degrade chlorobenzoates substituted at certain position. 3-chlorobenzoate is degraded 100% in two days, as well as 2-, 4-, and 3,5-chlorobenzoates are degraded 34%, 18% and 12.3% in seven days, respectively.(4) The plasmid purification and electrophoresis results show that Enterobacter sp. LY402 contains a 20kb plasmid, named pLYZ402. The plasmid deletion and transformation experiments indicate the genes of plasmid are related to PCB-degradation ability of LY402.(5) According to gene homolog, PCBs-degradation gene primers are designed. The genes are amplified by PCR using pLYZ402 template. Nearly complete bph gene cluster about 11kb is obtained. Homologous analysis shows that the gene organization and gene sequence of bph gene cluster are almost completely the same with that of Burkholderia xenovorans LB400. It is further confirmed that the gene cluster is localized in the pLYZ402 which is only about 1% of that of LB400. These also explain the similar degradation competence and substrate specificity between the two strains. It is postulated that plasmid carrying bph gene cluster maybe have good mobility in wild condition.(6) Primers of chlorobenzoate-degrading genes were designed according to the sequence of LB400. However, homologous gene is not isolated. The result shows that chlorobenzoate-degrading genes in Enterobacter sp. LY402 are probably not homolog with that of Burkholderia xenovorans LB400, and the isolation of related genes need further study.This paper presents that Enterobacter sp. LY402 degrades PCBs through bph pathway. In the process of degradation, chlorobenzoates are produced and chloride is released; twelve degrading genes localized in the 20kb plasmid pLYZ402, and constitute a gene cluster, while the gene sequence is homolog with that of LB400.