Enrichment of Microorganisms That Sequentially meta, para-Dechlorin- ate the Residue of Aroclor 1260 in Housatonic River Sediment

2,3,4,5,6-Pentachlorobiphenyl (23456-CB) primes a broad specificity meta-dechlorination (Process N) of Aroclor 1260 in Housatonic River sediments. We hypothesized that 23456-CB acts as an electron acceptor and could be used to selectively enrich PCB-dechlorinating microorganisms. Here we sought to (a) enrich the microbial population responsible for Process N dechlorination and (b) determine whether bioaugmentation with the enriched culture would stimulate effective PCB dechlorination. We made four serial transfers of actively dechlorinating slurries (10−20% of the final volume) plus 23456-CB to autoclaved PCB-contaminated sediment. The enrichment procedure greatly enhanced Process N dechlorination, reducing the hexa- through nonachlorobiphenyls in the sediment from 66.3 mol % initially to only 16.7 mol % in the fourth generation. The enrichment also fostered a new para-dechlorination activity (Process LP) that caused further conversion of Process N products to tri- and tetrachlorobiphenyls. Bioaugmentation without the primer resulted in only modest dechlorination. Our data demonstrate that enrichment with 23456-CB results in an inoculum that, when primed, rapidly and extensively dechlorinates weathered PCBs, even when excess oil is present. The identification of effective environmentally acceptable non-PCB agents to prime and enrich PCB dechlorinators could lead to a technology for in situ treatment of PCB-contaminated sediments.