Anaerobic biodegradation of polychlorinated biphenyls by a microbial consortium originated from uncontaminated paddy soil

Polychlorinated biphenyls (PCBs) in Kanechlor-300 and -400 mixtures dissipated significantly compared with a sterilized control under anaerobic conditions in three Japanese paddy soils with no history of PCB contamination, demonstrating the anaerobic microbial degradation of PCBs. The PCB-degrading activity was maintained successfully in a static flooded soil medium for more than 3 years by serial transfer at intervals of 56 days (13 transfers). Ortho-, meta-, and para-substituted PCBs, 15.2 +/- 9.9 mol% in total, were significantly degraded after 56 days of incubation. Analysis of menaquinones-6 and -7 and cloning of 16S rRNA gene fragments from a polymerase chain reaction denaturing gradient gel electrophoresis (DGGE) profile indicated the predominance of Firmicutes in the consortium. A PCR-based identification of the gene fragments showed the frequent presence of Desulfitobacterium sp., but not Dehalobacter sp. or Dehalococcoides sp., in the consortium. It is proposed that Japanese paddy soils with no history of PCB contamination contain an anaerobic microbial consortium consisting predominantly of Firmicutes that have the potential for anaerobic degradation of PCB.