Selective Degradation Of Polychlorinated Biphenyl By Enterobacter Sp. LY402 And Cloning And Expression Of Genes Of Biphenyl Dioxygense

Polychlorinated biphenyls(PCBs) are a class of compounds where the aromatic biphenyl skeleton carries between one and ten chlorine atoms and,theoretically,209 different PCB congeners can thus be produced.Enterobacter sp.LY402 can degrade PCBs efficiently. Some reports show that biphenyl dioxygense is the key enzyme of upper pathway of PCB. In this study,congener selectivity during polychlorinated biphenyl degradation by Enterobacter sp.LY402 was investigated.Cloning and expression of genes of biphenyl dioxygense were studied.To measure congener selectivity of Enterobacter sp.LY402 during polychlorinated biphenyls(PCBs) degradation,23 typical PCB congeners were chosen.(1)It was found that LY402 could effectively transform copla-nar 3,4,3',4'-tetrachlorobiphenyl at 0.05μM,it was degraded 50%by LY402 in 8 days.(2)The degradation rates of 2,4,5,2',3'-chlorobiphenyl(CB) and 2,4,5,2',4',5'-CB changed significantly when the sample constituents were different.These indicated that biore-mediation of individual congener was affected by others in the mixture. (3)Moreover,for PCBs containing one chlorine on each phenyl ring,the reactivity preference of LY402 was 2,2'-CB≥3,3'-CB＞＞4,4'-CB.PCBs con-taining two chlorines on either the ortho position of a single ring(i.e.,2,6-) or on both rings(i.e.,2,2'-),2,2'-CB was degraded more effectively than 2,6-CB.(4) Although 2,6-CB and 4,4'-CB were poorly degraded,after adding another or two chlorines,the biodegradability increased significantly.LY402 transformed 2,4,2',4'-CB and 2,4,4'-CB much more rapidly than 4,4'-CB,and 2,6,3'-CB was degraded rapidly than 2,6-CB.(5)Additionally,Comparing the two congeners of ortho-meta-chlorinated CB,2,3,2',3'-CB with neighbor meta chlorines was transformed slower than 2,5,2',5'-CB with interval meta chlorines.All these indicated that the transformation rates of PCBs were not consistent with the number of chlorines.PCBs containing same chlorines in numbers but different in position were converted quite different.In principle,influences of chlorine substituents on the degradation of PCBs by LY402 in turn were ortho-＞meta-＞para-CB.The bphA1A2A3A4 gene from pLYZ402(plasmid of Enterobacter sp.LY402),encoding the biphenyl dioxygense,was cloned and expressed.It is 4147bp.Firstly,bphA1A2 and bphA3A4 were cloned and expressed.Then the results showed that two genes were expressed at the same time,the expression of potential genes were inhibited,just as the expression of bphA2 and bphA4 were not detected.All the above results showed that the congener selectivity of LY402 were determined by many factors,including complexity of congener composition,location and number of chlorine substituent on the phenyl tings.Biphenyl dioxygense is an enzyme with complicated structure,so it must be avoided the adverse effects among four genes of biphenyl dioxygense for expression.