gUnseen majority in subsurface biospherehThis novel concept, which was presented by Whitman et al. in the Proceedings of National Academy Science of USA published in 1998, opened a door to the modern subsurface microbiology. Microorganisms from subground environments were recognized in the early 1920fs in oil reservoirs in USA but they had been minor research targets to scientists such as microbiologists, geologists and petroleum engineers before the paper by Whitman et al. We, a specific team in DEEPSTAR, JAMSTEC, already started our own research project called gSUGAR Project (Subground Animalcule Retrieval Project) having mission to subsurface biosphere. The newly presented
hypothesis strongly encouraged us and provoked increasing interest in subsurface microbiology around world. Historically, due to accessibility, the subsurface microbiology
has been conducted in terrestrial subsurface like deep underground water and deep oil reservoirs rather than in subseafloor environments. Knowledge of microbial components
in the terrestrial subsurface biosphere has been accumulated. To date, the presence of aerobic heterotrophs, anaerobic fermentative heterotrophs, dissimilatory iron-reducers, sulfatereducers and methanogens are known but only a few microbial components have been isolated and characterized from the deep subsurface biosphere. Fortunately, our research group has been succeeded in isolating novel subsurface microorganisms; a
hyper-alkaliphilic bacterium Alkaliphilus transvaalensis from a deep subsurface water at a depth of 3200 m in the South African gold mine (Fig. 1), an extremely thermophilic
bacterium Hydrogenobacter subterraneus from a 1500 m deep, superheated geothermal water pool in the Hacchoubaru geothermal electric plant. Very currently, a novel anoxic
hydrogen- or sulfur-oxidizing thermophile Sulfurihydrogenobium subterreneus has been isolated from subsurface hot aquifer water beneath the Hishikari gold mine. This microbe has long resisted to cultivation by many microbiologists and been recognized as gmysterious lifeh. As shown by an example of Sulfurihydrogenobium subterraneus,many of the subsurface microorganisms have novel characteristics that are quite different from and uncommon to those of surface microbial life. This means that subsurface To bring down the sensor to the direction of Earth depth or to dig in the sensor is a new development of observation. But, enhancement of observation network spreading across seabed is also essential. It is requested to link the observation networks organically and to make the information from holes three-dimensional in order to bring about universal Earth view.
Subseafloor biosphere has been much less understood than terrestrial subsurface biosphere. Preliminary microbiological surveys were undertaken by UK team (Parkes et al.) in the expeditions of Ocean Drilling Project (ODP) and revealed that considerable amounts of microorganisms were consistently distributed throughout drilled core obtained from approx. 1000 m below seafloor surface. However, the microbial population density measured by Parkes et al. was still controversial in relation with external microbial contamination with the service water used for drilling and the community structure, diversity and function of the subseafloor microbial components remained unclear. In the ODP expedition leg#185 for the Izu-Mariana trench area, the evaluation of the sample handling for microbiological investigation and the external microbial contamination during the drilling was for the first time performed. This work established the basis of the quality assessment and control (QA/QC) in the microbiological investigation in the ODP and has been a standard in the subsequent ODP cruises. The first strategic and systematic microbiological survey was organized in the ODP expedition leg#190 for the West Nankai Trough. Ongoing onshore research by UK and France team is focusing the vertical distribution and species composition of the microbial components in the ODP core. Most of the results seem to be very similar with the results that we had in the previous studies for the subseafloor environments in the Nankai Trough and Philippine Sea, and many of the molecular phylogenetic techniques appear to be imported by our preceding investigations. These are examples of our contribution to the international scientific society for subsurface microbiology. The ODP expedition leg#201 was the first cruise for subseafloor biospherein the long ODP history and was operated during January to April, 2002. The primary objective in this cruise was to clarify the relationship between geochemical and microbiological processes of sulfate and methane in the subseafloor sediments in the Peru Margin. From Japan, Dr. Inagaki, a member of SUGAR Project, joined the onboard party and was in charge of bio-mapping and cultivation of microbial components associated with sulfate and methane metabolisms.
The ODP expedition leg#201 was the first cruise for subseafloor biospherein the long ODP history and was operated during January to April, 2002. The primary objective in this cruise was to clarify the relationship between geochemical and microbiological processes of sulfate and methane in the subseafloor sediments in the Peru Margin. From Japan, Dr.
Inagaki, a member of SUGAR Project, joined the onboard party and was in charge of bio-mapping and cultivation of microbial components associated with sulfate and methane metabolisms.
The newly obtained results will be reported in the Goldschmidt 2002 and International Symposium for Subsurface Microbiology (ISSM) 2002 in coming summer and will give important insight into the subseafloor biosphere. In addition, the ODP expedition leg#201 induced not only the high quality of research on subseafloor biosphere but also the new framework of international co-operation and competence in the subsurface microbiology. The contribution of Japanese microbiologist to the international society of subsurface microbiology will be further required.
The OD21, a brandnew ocean drilling project in the 21st century, is now starting. gCHIKYUh is a riser deep-sea drilling vessel and serves as the main platform of the OD21. CHIKYUh will make it possible to explore the deep and active zones of the earthfs crust resisting to the drilling operation by a non-riser drilling vessel gJoides Resolutionh. We, subsurface microbiologists, are enthusiastic to have opportunities for exploration to gsubvent biosphereh beneath active deep-sea hydrothermal seafloor, to extremely high-pressurized free-gas zone far below subseafloor methane hydrate strata as a potential biogenic methane-production area and to goil-reservoirbiosphereh. We are now the most interested in drilling into the deep-sea hydrothermal vent field at the Iheya Ridges in the middle Okinawa Trough and the gas hydrate area in the Nankai Trough.
Based on the geomicrobiological investigation to the microbial communities in the deep-sea hydrothermal vent fields in the Central Indian Ridge and the middle Okinawa Trough using gSHINKAI6500h and gSHINKAI2000h, we have evidences that hyperthermophilic subsurface lithoautotrophic microbial ecosystem (HyperSLiME) is present beneath active hydrothermal seafloor. The photosynthesis-independent, microbial ecosystem utilizing energy and carbon solely provided from the earthfs interior is an analogous ecosystem of the extraterrestrial life in other planets and the search for SLiME is heated up. Our data for the first time indicated that hyperthermophilic methanogens might be abundant in the subvent environments and serve as the primary producer of the gearth-eatingh ecosystem using hydrogen and carbon dioxide geochemically provided from the interior of the earth's crust. The proposal for drilling into the subvent HyperSLiME in the mid-Okinawa Trough is under preparation. The proposed expedition will directly prove the existence of the subvent biosphere and HyperSLiME and shed light on the origin of life and the early evolution of microbial ecosystems.
In the subduction zone in the Nankai Trough, it is observed that a large amount of subseafloor methane hydrate deposit is widely distributed. The subsurface methane hydrate deposit is recognized as the new energy resource alternating petroleum in the 21st century and as an important factor inducing catastrophic environmental change of the past and present earth. Despite great interest in the subsurface methane hydrate deposit, the synthesis mechanism of the methane and the formation and dissociation processes of the gas hydrate are still unclear. The carbon isotopic analysis of methane in the methane hydrate from the Nankai Trough suggested the biogenic origin of the methane, however no apparent signature for existence and activity of methanogens has been discovered from the subseafloor methane hydrate strata and the shallower zones. Towards this query, we have a hypothesis that the methane is produced by hyperthermophilic methangens in the hotter and deeper zones than in the present methane hydrate deposit and the upwelling free-gas of methane forms the hydrate structure according to the physicochemical equilibrium. To prove this hypothesis, we need a very deep drilling operation penetrating the methane hydrate strata into high-temperature and high-pressure free-gas zones, in which active population of hyperthermophilic methanogens is present. The deep drilling beneath the methane hydrate deposit has been inhibited in the non-riser drilling vessel from aspects of safe and environmental pollution. gCHIKYUh will make it possible! What kinds of methanogens support the methane hydrate in the Nankai Trough? We are picking up a member of Methanothermococcus okinawensis (Fig. 2) as the most plausible candidate. The genetic signature