title: Occurrence and potential activity of denitrifiers and methanogens in groundwater at 140 m depth in Pliocene diatomaceous mudstone of northern Japan.
abstract: Anaerobic microbial activity has a major influence on the subsurface environment. We investigated the denitrification and methanogenesis in anoxic groundwater at a depth of 140 m in two boreholes drilled in a sedimentary geological setting, where the redox potential fluctuated. The average maximum potential denitrification rates, measured under anaerobic conditions in the two boreholes using an (15) N tracer, were 0.060 and 0.085 nmol (30) N2  mL(-1)  h(-1) . The deduced NirS amino acid sequences obtained from in situ samples were similar to those of isolates belonging to the α-, β-, and γ-Proteobacteria, and the Firmicutes (72-100% similarity). Based on the nirS gene, the same operational taxonomic unit dominated incubated samples from each borehole. Methanogenesis candidates were detected by 16S rRNA gene analysis, but no sequence was detected using primers for the functional methanogenesis gene mcrA. Although the stable isotope signatures suggested that some of the dissolved methane was of biogenic origin, no potential for methane production was evident during the incubations. The groundwater at 140 m depth did not contain oxygen, had an Eh ranging from -144 to 6.8 mV, and was found to be a potential field for denitrification.
authors.affiliation: Department of Geosciences, Faculty of Science, Shizuoka University, Shizuoka, Japan; Department of Biological Sciences, Faculty of Science and Engineering, Chuo University, Tokyo, Japan.
authors.forename: Chie
authors.initials: C
authors.lastname: Katsuyama
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Nashimoto
authors.forename: Kazuyo
authors.initials: K
authors.lastname: Nagaosa
authors.forename: Tomotaka
authors.initials: T
authors.lastname: Ishibashi
authors.forename: Kazuki
authors.initials: K
authors.lastname: Furuta
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kinoshita
authors.forename: Hideki
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Aoki
authors.forename: Takahiro
authors.initials: T
authors.lastname: Asano
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Sasaki
authors.forename: Rumi
authors.initials: R
authors.lastname: Sohrin
authors.forename: Daisuke D
authors.initials: DD
authors.lastname: Komatsu
authors.forename: Urumu
authors.initials: U
authors.lastname: Tsunogai
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kimura
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Suwa
authors.forename: Kenji
authors.initials: K
authors.lastname: Kato
mesh_terms: D001105:Archaea / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D058440:Denitrification; D020459:Genes, rRNA; D019015:Geologic Sediments / Q000382:microbiology*; D060587:Groundwater / Q000382:microbiology*; D007564:Japan; D008697:Methane / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D020560:Proteobacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics
chemical_list: D012336:RNA, Ribosomal, 16S; D008697:Methane
keywords: 15N tracer; denitrification; methanogenesis; redox potential; sedimentary rock; stable isotope