Although polychlorinated biphenyls (PCBs) are persistent environmental contaminants, they are susceptible to biodegradation processes in sediments. Anaerobic bacteria, primarily from the phylum Chloroflexi, use more highly chlorinated PCB congeners as electron acceptors and dechlorinate them with anaerobic reductive dehalogenase enzymes. Certain aerobic bacteria attack the lighter chlorinated congeners with biphenyl dioxygenase, leading to ring cleavage and eventual mineralization of PCBs. We have examined PCB biodegradation potential in sediment cores from Indiana Harbor and Ship Canal near Chicago, IL (IHSC; total PCB concentrations about 12.5 mg/kg) and in 27 surficial sediment samples from a wastewater lagoon located in Altavista, VA (AWL; total PCB concentrations up to 4300 mg/kg). At IHSC, sediment PCB congener profile analysis indicated a strong Arochlor 1248 signal that weakened with depth. This was attributed to increased abundance of lightly chlorinated congeners (1-3 chlorines) with a corresponding decrease in congeners containing 4-6 chlorines. At AWL, sediment samples displayed a strong Arochlor 1242 signal, except for one which contained mostly PCBs with 1-4 chlorines. PCB dechlorination processes were likely responsible for the altered congener profiles at both sites. DNA was extracted from sediment samples for molecular biology analyses. IHSC sediment DNA was subjected to quantitative PCR (qPCR) and terminal restriction fragment length polymorphism (T-RFLP) analysis. AWL sediments were subjected to Illumina 16S rRNA gene sequencing and qPCR. At IHSC putative dechlorinating Chloroflexi 16S genes and biphenyl dioxygenases genes (~10<sup>6</sup> genes/g sediment) co-occurred and were elevated between 0.5 – 2 m depth in the sediments.At AWL, putative dechlorinating Chloroflexi 16S sequences were noted, but at relatively low abundance. BphA gene abundance at AWL was about an order of magnitude lower than observed at IHSC. Additional qPCR analyses for reductive dehalogenase genes are planned for AWL sediments. We will also confirm the presence of PCB dechlorinators in AWL sediment microcosms.

Investigating polychlorinated biphenyl biodegradation potential in contaminated sediments with chemical and molecular biology approaches

253rd National Meeting (2017)

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