Marine Ecosystems Research Department - jamstec japan agency ...

Japan Marine Science and Technology Center
Frontier Research System for Extremophiles
able community structures and distribution profiles of
each member in the chimney structures and substrata of
ISCSs were highly fluctuated at each vent site, although
geochemical analyses indicated the hydrothermal fluids
from each vent had the identical origin. Especially culturable
population of methanogen were prominent in
two substrata of ISCSs deployed into hydrothermal
conduits for two years, suggesting the vent fluids from
the vents contained a large amount of viable
methanogens and the occurrence of indigenous population
of methanogen at subvent biosphere beneath those
vent sites. These characteristic distribution profiles of
viable microorganisms indicate that microbial population
which could be detected above the seafloor of
hydrothermal systems probably reflected the microbial
populations occurring at subvent biosphere associating
with hydrological structure beneath the seafloor.
(c) ODP Leg. Subseafloor biosphere in the Peru
Margin
The subseafloor environment has been proposed to
be the largest biosphere on Earth, as based on estimates
of cells in marine sediment cores recovered by
the Ocean Drilling Program (ODP). However, it is not
well-known what kinds of microorganisms are present,
how their distributions relate with geological settings,
and how their metabolic activities impact the
global geochemical cycles. The ODP Leg. took
place in the eastern equatorial Pacific and Peru coastal
margin in , and was the first expedition in ODP
history targeted mainly on microbiology and biogeochemistry
in the subseafloor biosphere. In this expedition,
we investigated the vertical profile data of the
results from culture-independent molecular ecological
surveys in ODP sediment core columns collected from
the two drilling sites, and , located on the
land slope of the accretionary wedge in the Peru
Trench. The sediment cores recovered from Site
contained high organic carbon and methane, whereas
those from Site contained low concentrations of
these chemical components. Bulk prokaryotic nucleic
acids were extacted and purified from each sediment,
and S rRNA genes (rDNA) were amplified by PCR
using domain specific primers. The analyses of rDNA
sequences of clone libraries, quantitative-PCR for
archaeal and bacterial rDNA, and T-RFLP fingerprint
analysis revealed the previously unknown vertical distribution
and diversity of Archaea and Bacteria in two
geologically discrete subseafloor environments.
(d) IMAGES Subseafloor Biosphere in the southwestern
Sea of Okhotsk
Microbial communities from a subseafloor sediment
core from the southwestern Sea of Okhotsk were evaluated
using both cultivation-dependent and -independent
(molecular) analyses. The core, which extended .
meters below the seafloor (mbsf), was composed of
pelagic clay with several volcanic ash layers containing
fine pumice grains. Direct cell counts and quantitative-
PCR (qPCR) analysis of archaeal and bacterial S
ribosomal RNA gene (rDNA) fragments indicated that
the bacterial populations in ash layers were approximately
- times higher than those in the clays. Partial
sequences of rDNA clones revealed qualitative
differences in the microbial communities from the two
different layers. Two phylogenetically distinct archaeal
assemblages within the Crenarchaeota, MCG
(Miscellaneous Crenarchaeotic Group) and DSAG
(Deep-Sea Archaeal Group), were the most predominant
archaeal rDNA components in ash layers and
pelagic clays, respectively. Proteobacterial rDNA within
the gamma-Proteobacteria dominated the ash layers,
whereas the sequences within the candidate division
OP and the green non-sulfur bacteria dominated the
pelagic clay environments. Molecular (S rDNA
sequence analysis) of isolated colonies revealed a
regional proliferation of viable heterotrophic
mesophiles in the volcanic ash layers, along with some
Gram-positives and Actinobacteria. The porous ash layers,
ranging in age from tens to hundreds of thousands
of years, thus appear to be discrete microbial habitats
within the coastal subseafloor clay sediment, capable of
harboring microbial communities very distinct from
those seen in the more abundant pelagic clays.
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