Environmental Engineering Reference
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be the predominant archaeal components in habitats of deep-sea hydrother-
mal vent environments, we suggest that
Thermococcus
, DHVE and
Haloarcula
cells are most likely derived from the hydrothermally active environments sur-
rounding the Philippine Sea such as the Izu-Bonin arc, Mariana arc, and Manus
Basin (Fig. 2). Given the slow rate of ocean crust movement (a few cm/yr), the
sediments themselves are still within 10-20 km of their location 2 million years
ago, so other mechanisms must account for the results, such as sea-bottom
currents, which might be one mode of transport of these cells. The extreme
thermoacidophilic Archaea,
Sulfolobus-Sulfurisphaera
, might be derived from
the terrestrial geothermal environments by the regional west wind (Fig. 2). In-
deed, a representative sequence was closely related to the sequence of
Sufolobus
yangmingensis
isolated from a hot spring in Taiwan [23]. Interestingly, these
molecular signals were obtained from just beneath the volcanic ash layers. On
the basis of these results, it may be possible to say that the molecular signals
of terrestrial extremophiles are likely to be a good indicator of the geothermal
activities before the volcanic eruptions.
Although the clonal frequency does not reflect the cell abundance because
of the occurrence of bias during PCR and cloning steps and the copy number
of 16S rRNA gene in genome, the results showed that the archaeal community
structures were mixed with paleomes of extremophiles in marine and terrestrial
environments and the compositions of these phylotypes changed with the age of
the sediment horizons. For example, the sequences related to
Haloarcula
were
only detected in a depth range from 7.8 to 12.8 mbsf deposited 1-2 million
years ago. High numbers of the
Sulfolobales
clone sequences were found only
just beneath the events of the volcanic eruption (Fig. 1). These facts suggest
that the archaeal communities buried from the Pleistocene period, more than 2
million years, might reflect the past geologic thermal activities surrounding the
sampling site in the Philippine Sea (Fig. 2). The paleomic signals may give us
new insights as geomicrobiological evidences into paleo-proxies that have not
been identified by conventional geologic surveys.
2.2 Unusual Endolithic Prokaryotes in a Deep-Sea
Sedimentary Rock
While analysis of core samples is the usual approach for the investigation of
sedimentary materials, there are other less obvious opportunities that occasion-
ally arise. For example, the Japan Trench is recognized as a typical erosion-type
subduction zone where frequent earthquakes occur. The associated seismic and
subduction activities can lead to the movement of sedimentary rocks to the
deep parts of the trench where they are found as dropstones. In May 1999, we
collected such a rock sample from the Japan Trench at a depth of 6,337 m using
the manned submersible Shinkai6500 and examined the microbial communities
