Conjugative Transfer Of Dioxin-catabolic Megaplasmids And Bioaugmentation Prospects Of Rhodococcus Sp.strain P52

Dioxins include polychlorinated dibenzo-p-dioxin(PCDDs)and polychlorinated dibenzofuran(PCDFs),can potentially induce developmental toxicity,cancers and they are known to be extremely persistent in the environment.Because the conventional physical and chemical treatment methods for dioxins are diseconomy,enhancing the biodegradation process is a promising strategy to restore dioxin-contaminated environment.In our previous studies,an isolated dioxin-degrader Rhodococcus sp.strain p52 has been found that this strain has two distinct gene clusters encoding angular dioxygenases,DfdA and DbfA,for dioxin degradation.And they are located on two plasmids,pDF01 and pDF02,respectively.In the present study,we performed mating experiments using strain p52 as a donor and bacterial strains belong to different genera as recipients.The results showed that pDF01 and pDF02 were unstable in other transconjugants,except the Pseudomonas aeruginosa transconjugants,and pDF01 and pDF02 transferred concomitantly from strain p52 to P.aeruginosa strain at a conjugation frequency of 3×10-4 colonies per recipient.Further,pDF01 and pDF02 were isolated from the P.aeruginosa transconjugant and identified by Southern hybridization,and they were localized in the transconjugant cells by fluorescence in situ hybridization.Moreover,the catabolic plasmids functioned in the transconjugant,which gained the ability to use dibenzofuran and chlorodibenzofuran for growth,and they were maintained in the transconjugant for at least 40 generations without selective pressure.Furthermore,conjugative transfer of the catabolic plasmids to activated sludge bacteria was detected.We isolated an Arthrobacter sp.transconjugant from the sludge bacteria and identified pDF01 and pDF02 by Southern hybridization.The Arthrobacter sp.transconjugant,which gained the ability to use dibenzofuran for growth,could degraded DF(500 mg/L)completely within 90 h.Sequencing of pDF01 and pDF02 revealed the genetic basis for the plasmids' conjugative transfer and stable maintenance.Therefore,strain p52 harboring pDF01 and pDF02 has potential for genetic bioaugmentation in dioxin-contaminated environments.