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Applied and Environmental Microbiology, December 2005, p. 8085-8090, Vol. 71, No. 12
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.12.8085-8090.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Sequential Reductive Dechlorination of meta-Chlorinated Polychlorinated Biphenyl Congeners in Sediment Microcosms by Two Different Chloroflexi Phylotypes
Sonja K. Fagervold,1 Joy E. M. Watts,2 Harold D. May,3 and Kevin R. Sowers1*Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, Maryland,1 Biological Sciences, Towson University, Towson, Maryland,2 Department of Microbiology and Immunology, Medical University of South Carolina, Charleston, South Carolina3
Received 4 May 2005/ Accepted 2 September 2005
Three species within a deeply branching cluster of the Chloroflexi are the only microorganisms currently known to anaerobically transform polychlorinated biphenyls (PCBs) by the mechanism of reductive dechlorination. A selective PCR primer set was designed that amplifies the 16S rRNA genes of a monophyletic group within the Chloroflexi including Dehalococcoides spp. and the o-17/DF-1 group. Assays for both qualitative and quantitative analyses by denaturing gradient gel electrophoresis and most probable number-PCR, respectively, were developed to assess sediment microcosm enrichments that reductively dechlorinated PCBs 101 (2,2',4,5,5'-CB) and 132 (2,2',3,3',4,6'-CB). PCB 101 was reductively dechlorinated at the para-flanked meta position to PCB 49 (2,2',4,5'-CB) by phylotype DEH10, which belongs to the Dehalococcoides group. This same species reductively dechlorinated the para- and ortho-flanked meta-chlorine of PCB 132 to PCB 91 (2,2',3',4,6'-CB). However, another phylotype designated SF1, which is more closely related to the o-17/DF-1 group, was responsible for the subsequent dechlorination of PCB 91 to PCB 51 (2,2',4,6'-CB). Using the selective primer set, an increase in 16S rRNA gene copies was observed only with actively dechlorinating cultures, indicating that PCB-dechlorinating activities by both phylotype DEH10 and SF1 were linked to growth. The results suggest that individual species within the Chloroflexi exhibit a limited range of congener specificities and that a relatively diverse community of species within a deeply branching group of Chloroflexi with complementary congener specificities is likely required for the reductive dechlorination of different PCBs congeners in the environment.
* Corresponding author. Mailing address: Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, MD 21202. Phone: (410) 234-8878. Fax: (410) 234-8896. E-mail: sowers{at}umbi.umd.edu.
Applied and Environmental Microbiology, December 2005, p. 8085-8090, Vol. 71, No. 12
0099-2240/05/$08.00+0 doi:10.1128/AEM.71.12.8085-8090.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
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