title: Cultivation of methanogenic community from subseafloor sediments using a continuous-flow bioreactor.
abstract: Microbial methanogenesis in subseafloor sediments is a key process in the carbon cycle on the Earth. However, the cultivation-dependent evidences have been poorly demonstrated. Here we report the cultivation of a methanogenic microbial consortium from subseafloor sediments using a continuous-flow-type bioreactor with polyurethane sponges as microbial habitats, called down-flow hanging sponge (DHS) reactor. We anaerobically incubated methane-rich core sediments collected from off Shimokita Peninsula, Japan, for 826 days in the reactor at 10 °C. Synthetic seawater supplemented with glucose, yeast extract, acetate and propionate as potential energy sources was provided into the reactor. After 289 days of operation, microbiological methane production became evident. Fluorescence in situ hybridization analysis revealed the presence of metabolically active microbial cells with various morphologies in the reactor. DNA- and RNA-based phylogenetic analyses targeting 16S rRNA indicated the successful growth of phylogenetically diverse microbial components during cultivation in the reactor. Most of the phylotypes in the reactor, once it made methane, were more closely related to culture sequences than to the subsurface environmental sequence. Potentially methanogenic phylotypes related to the genera Methanobacterium, Methanococcoides and Methanosarcina were predominantly detected concomitantly with methane production, while uncultured archaeal phylotypes were also detected. Using the methanogenic community enrichment as subsequent inocula, traditional batch-type cultivations led to the successful isolation of several anaerobic microbes including those methanogens. Our results substantiate that the DHS bioreactor is a useful system for the enrichment of numerous fastidious microbes from subseafloor sediments and will enable the physiological and ecological characterization of pure cultures of previously uncultivated subseafloor microbial life.
authors.affiliation: Subsurface Geobiology Advanced Research (SUGAR) Project, Extremobiosphere Research Program, Institute of Biogeosciences, Japan Agency for Marine-Earth Science & Technology (JAMSTEC), Yokosuka, Kanagawa, Japan. imachi@jamstec.go.jp
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Imachi
authors.forename: Ken
authors.initials: K
authors.lastname: Aoi
authors.forename: Eiji
authors.initials: E
authors.lastname: Tasumi
authors.forename: Yumi
authors.initials: Y
authors.lastname: Saito
authors.forename: Yuko
authors.initials: Y
authors.lastname: Yamanaka
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Saito
authors.forename: Takashi
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tomaru
authors.forename: Rika
authors.initials: R
authors.lastname: Takeuchi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Morono
authors.forename: Fumio
authors.initials: F
authors.lastname: Inagaki
authors.forename: Ken
authors.initials: K
authors.lastname: Takai
mesh_terms: D001105:Archaea / Q000145:classification / Q000235:genetics; D019149:Bioreactors; D017753:Ecosystem; D019605:Euryarchaeota / Q000235:genetics; D019015:Geologic Sediments / Q000382:microbiology*; D007564:Japan; D008697:Methane / Q000378:metabolism*; D017014:Methanobacterium / Q000235:genetics; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012623:Seawater / Q000382:microbiology*; D013696:Temperature
chemical_list: D012336:RNA, Ribosomal, 16S; D008697:Methane