title: Distribution of dehalogenation activity in subseafloor sediments of the Nankai Trough subduction zone.
abstract: Halogenated organic matter buried in marine subsurface sediment may serve as a source of electron acceptors for anaerobic respiration of subseafloor microbes. Detection of a diverse array of reductive dehalogenase-homologous (rdhA) genes suggests that subseafloor organohalide-respiring microbial communities may play significant ecological roles in the biogeochemical carbon and halogen cycle in the subseafloor biosphere. We report here the spatial distribution of dehalogenation activity in the Nankai Trough plate-subduction zone of the northwest Pacific off the Kii Peninsula of Japan. Incubation experiments with slurries of sediment collected at various depths and locations showed that degradation of several organohalides tested only occurred in the shallow sedimentary basin, down to 4.7 metres below the seafloor, despite detection of rdhA in the deeper sediments. We studied the phylogenetic diversity of the metabolically active microbes in positive enrichment cultures by extracting RNA, and found that Desulfuromonadales bacteria predominate. In addition, for the isolation of genes involved in the dehalogenation reaction, we performed a substrate-induced gene expression screening on DNA extracted from the enrichment cultures. Diverse DNA fragments were obtained and some of them showed best BLAST hit to known organohalide respirers such as Dehalococcoides, whereas no functionally known dehalogenation-related genes such as rdhA were found, indicating the need to improve the molecular approach to assess functional genes for organohalide respiration.
authors.affiliation: Geomicrobiology Group, Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Monobe B200, Nankoku, Kochi 783-8502, Japan.
authors.forename: Taiki
authors.initials: T
authors.lastname: Futagami
authors.forename: Yuki
authors.initials: Y
authors.lastname: Morono
authors.forename: Takeshi
authors.initials: T
authors.lastname: Terada
authors.forename: Anna H
authors.initials: AH
authors.lastname: Kaksonen
authors.forename: Fumio
authors.initials: F
authors.lastname: Inagaki
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000378:metabolism; D001431:Bacteriological Techniques / Q000379:methods; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D020459:Genes, rRNA; D014644:Genetic Variation; D019015:Geologic Sediments / Q000032:analysis / Q000382:microbiology*; D054879:Halogenation; D007564:Japan; D015205:Northwestern United States; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010636:Phenols / Q000378:metabolism; D010802:Phylogeny; D012329:RNA, Bacterial / Q000032:analysis* / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000032:analysis / Q000235:genetics; D012623:Seawater / Q000382:microbiology; D014871:Water Microbiology
chemical_list: D010636:Phenols; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; C066859:2,4,6-triiodophenol; D010088:Oxidoreductases; C004554:2,4,6-tribromophenol