Characteristic And Substituted Electron Acceptor Of Polychorinated Biphenyls-dechlorinating Cultures

Polychlorinated biphenyls(PCBs)were ever manufactured as complex mixture such as Aroclor and widely used in industry for various applications.PCBs are known to be lipophilic,toxic,persistent pollutants and apt to bioaccumulation in food chain,posing risk to human health and the environment.Dechlorination,converting higher-chlorinated congeners to lower-chlorinated forms,is the critical process for thoroughly degradation of highly chlorinated congeners.Due to extremely low solubity of PCBs in water and slow growth rate of bacteria,dechlorinators are difficult to grow on PCBs in absence of sediments or sediment substitutes,impeding further identification and characterization of PCB-dechlorinating bacteria.A sediment-free enrichment culture PSCB derived from paddy soil could carry out efficient dechlorination of Aroclor 1260 through removing singly and doubly franked meta chlorines according to Dechlorination Process N.86.0%,91.5%and 76.6%,respectively of hexa-,hepta-and octa-CB were transformed in 64 days.The average number of chlorines per biphenyl decreased from 6.4 to 4.5.The dechlorination rate was more efficient than previous sediment-free cultures.The dechlorinator Dehalococcoides group represented only 1.37%of total microorganism.PCBs reductive dechlorination homologe genes,pcbA4 and pcbA5,were amplified in PSCB culture.qPCR results proved that Dehalococcoides cell and pcbA4 and pcbA5 gene copy numbers were involved with the dechlorination of Aroclor 1260.However,pcbA4 and pcbA5 gene copy numbers were far less than Dehalococcoides16S rRNA gene,suggesting the possibility of presence of multiple Dehalococcoide.s strains carrying distinct RDases contributing to chlorine removal.The growth rate of Dehalococcoides group in PCE-fed culture was 6 times than that of PCB-fed culture.PCE-fed culture performed the identical PCB-dechlorination pathway with PCB-fed cultures.However,the PCB-dechlorination rate of PCE-fed culture was 17 times faster than that of PCB-fed culture.The high-efficient enrichment cultures of dechlorinators in sediment-free media facilitate screening PCB dechlorinators and identification of novel PCB RDases,and meanwhile,show promise for mass culturing of inoculum for bioaugmentation.