title: Sequential reductive dechlorination of meta-chlorinated polychlorinated biphenyl congeners in sediment microcosms by two different Chloroflexi phylotypes.
abstract: 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.
authors.affiliation: Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, MD 21202, USA.
authors.forename: Sonja K
authors.initials: SK
authors.lastname: Fagervold
authors.forename: Joy E M
authors.initials: JE
authors.lastname: Watts
authors.forename: Harold D
authors.initials: HD
authors.lastname: May
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Sowers
mesh_terms: D000693:Anaerobiosis; D001483:Base Sequence; D001711:Biotransformation; D002713:Chlorine / Q000032:analysis*; D041862:Chloroflexi / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers; D019015:Geologic Sediments / Q000737:chemistry*; D010802:Phylogeny; D011078:Polychlorinated Biphenyls / Q000737:chemistry* / Q000493:pharmacokinetics; D016133:Polymerase Chain Reaction; D012329:RNA, Bacterial / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D017931:DNA Primers; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D002713:Chlorine; D011078:Polychlorinated Biphenyls