title: Unique distribution of deep groundwater bacteria constrained by geological setting.
abstract: We collected groundwater samples at depths of up to 482 m from three boreholes drilled into sedimentary rock within two formations in Hokkaido, Japan. The prokaryotic community in each subsurface groundwater sample was analysed by microscopic counts and cloning-sequencing the 16S rRNA genes. On total direct counts, there were between 4.61 × 10(4) and 5.06 × 10(6) prokaryote cells ml(-1) in the samples, which is similar to the numbers observed at the marine subsurface. However, the vertical distribution of the prokaryotes did not show a simple decrease in abundance with increasing depth. A high abundance of cells with significant amounts of RNA was identified in the domain Bacteria using fluorescence in situ hybridization, with a high frequency of dividing cells at the transition zone between the two sedimentary rock formations. Cloning-sequencing analysis showed the predominance of γ-Proteobacteria at this transition zone at 281-312 m. The horizontal heterogeneity of the microbial distribution in the subsurface environment was also demonstrated by a relatively high density of members of the domain Archaea in borehole HDB-4, drilled only 1.5 km northeast of HDB-6 and in the same formation.
authors.affiliation: Department of Geosciences, Faculty of Science, Shizuoka University, 836 Oya, Suruga-ku, Shizuoka 422-8529, Japan. Horonobe Underground Research Center, Japan Atomic Energy Agency, 432-2 Hokushin, Horonobe-cho, Teshio-gun, Hokkaido 098-3224, Japan. Earth and Planetary System Science, Faculty of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo 060-0810, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Kato
authors.forename: Kazuyo
authors.initials: K
authors.lastname: Nagaosa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kimura
authors.forename: Chie
authors.initials: C
authors.lastname: Katsuyama
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Hama
authors.forename: Takanori
authors.initials: T
authors.lastname: Kunimaru
authors.forename: Urumu
authors.initials: U
authors.lastname: Tsunogai
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Aoki