title: Novel uncultured Chloroflexi dechlorinate perchloroethene to trans-dichloroethene in tidal flat sediments.
abstract: The marine environment represents a rich source of bio- and geogenically produced organohalogens, including the common pollutant perchloroethene (PCE). However, diversity and function of marine chloroethene-dechlorinating microorganisms are largely unknown. Here, we have studied the activity and composition of a tidal flat sediment bacterial and archaeal community from the North Sea exposed to low concentrations of PCE. After 2 weeks of incubation, PCE was rapidly dechlorinated via trichloroethene to dichloroethene (DCE). Unexpectedly, these microcosms produced 3.5-fold more trans-DCE than cis-DCE. The actively dechlorinating microbial populations were traced by stable isotope probing of rRNA with (13)C-labelled acetate for 4 days. Terminal restriction fragment length polymorphism fingerprinting and clone libraries of isotopically enriched, 'heavy'(13)C-labelled bacterial 16S rRNA revealed the populations potentially involved in reductive dechlorination. Major clone groups belonged to the Proteobacteria (50.0%; 22.4% delta-, 12.1% gamma-, 6.9% alpha-, 6.9% beta- and 1.7% epsilon-subgroup) and Chloroflexi (29.3%). Populations represented by the two dominant terminal restriction fragments were affiliated with the Dehalococcoidetes (subphylum II of the Chloroflexi), and were exclusively detected in the heavy fraction of the PCE-dechlorinating incubation. The phylogenetically novel, larger population, designated Tidal Flat Chloroflexi Cluster, was closely related to the recently discovered PCE-dechlorinating Lahn Cluster bacteria from anoxic river sediment but more distantly related to canonical Dehalococcoides spp. (92-94% sequence identity). The second population was closely related to 'Dehalobium chlorocoercia DF-1'. Both populations appear to be responsible for reductive dechlorination of highly chlorinated ethenes to predominantly trans-DCE in tidal flat sediment incubations.
authors.affiliation: Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch Strasse, Marburg, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Kittelmann
authors.forename: Michael W
authors.initials: MW
authors.lastname: Friedrich
mesh_terms: D019342:Acetic Acid / Q000378:metabolism; D002247:Carbon Isotopes / Q000378:metabolism; D002713:Chlorine / Q000378:metabolism*; D041862:Chloroflexi / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D019015:Geologic Sediments / Q000382:microbiology*; D006843:Hydrocarbons, Chlorinated / Q000378:metabolism*; D007553:Isotope Labeling; D008969:Molecular Sequence Data; D009659:North Sea; D010802:Phylogeny; D012150:Polymorphism, Restriction Fragment Length; D020560:Proteobacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes; D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D006843:Hydrocarbons, Chlorinated; D012336:RNA, Ribosomal, 16S; D002713:Chlorine; D019342:Acetic Acid