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Appl. Environ. Microbiol. doi:10.1128/AEM.02909-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Dehalococcoides in a Sediment-Free, Mixed Culture Metabolically Dechlorinate the Commercial Polychlorinated Biphenyl Mixture Aroclor 1260

Department of Biology, Rensselaer Polytechnic Institute, Troy, NY 12180, USA; School of Civil and Environmental Engineering and; School of Biology, Georgia Institute of Technology, Atlanta, GA 30332, USA

^* To whom correspondence should be addressed. Email: bedard{at}rpi.edu.

	Abstract

Microbial reductive dechlorination of commercial polychlorinated biphenyl (PCB) mixtures (e.g. Aroclors) in aquatic sediments is crucial to achieve detoxification. Despite extensive efforts over nearly two decades, the microorganisms responsible for Aroclor dechlorination remained elusive. Here we demonstrate that anaerobic bacteria of the Dehalococcoides group derived from Housatonic River sediment (Massachusetts, USA) simultaneously dechlorinate 64 PCB congeners carrying 4 to 9 chlorines in Aroclor 1260 in the sediment-free JN cultures. Quantitative real-time PCR showed that the Dehalococcoides cell titer increased from 7.07 x 10⁶ ± 0.42 x 10⁶ to 1.67 x 10⁸ ± 0.04 x 10⁸ cells/ml concomitant with a 64.2% decrease of the PCBs with 6 chlorines in Aroclor 1260 in JN cultures amended with acetate and hydrogen. No Dehalococcoides growth occurred in parallel cultures without PCBs. Aroclor 1260 dechlorination supported the growth of 9.25 x 10⁸ ± 0.04 x 10⁸ Dehalococcoides cells per µmole of chlorine removed. 16S rRNA gene-targeted PCR analysis of known dechlorinators (i.e., Desulfitobacterium, Dehalobacter, Desulfuromonas, Sulfurospirillum, Anaeromyxobacter, Geobacter, and o-17/DF-1 Chloroflexi) ruled out any involvement of these bacterial groups in the dechlorination. Our results suggest that the Dehalococcoides population present in the JN cultures also catalyzes in situ dechlorination of Aroclor 1260 in the Housatonic River. The identification of Dehalococcoides as catalysts of extensive Aroclor 1260 dechlorination and our ability to propagate the JN cultures under defined conditions offer opportunities to study the organisms' ecophysiology, elucidate nutritional requirements, identify reductive dehalogenase genes involved in PCB dechlorination, and design molecular tools required for bioremediation applications.

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