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    Microorganisms have co-evolved with Earth over 3.4 billions years during which environmental dynamics would shape the distribution, assemblage, and function of microbial communities, and conversely elemental cycling among hydrosphere, atmosphere and lithosphere is in part driven by microorganisms. Such an interaction between life and environment during geological times could possibly leave signatures preserved within rock records, and be inferred with appropriate modern analogs. When seeking to unravel the extent of biosphere, the microbe-mineral interaction, the metabolic machinery and evolutionary trait of ecosystem, the emergence of life on Earth, and the potential of extant life on extraterrestrial bodies, both biological and geochemical sets of data should be coherently reconciled. Modern terrestrial hydrothermal system appears to be the best target to address these questions from various aspects that require the cross-link between biology and geology through the following rationales:

(1) Previous studies already attested that (hyper)thermophiles may shed light on the evolution of early biosphere since their positions in the phylogenetic tree based on 16S rRNA genes all cluster near the so-called “universal ancestor”. This evolutionary trait is consistent with the consensus that the surface of early Earth was hot enough for the proliferation of only (hyper)thermophiles. The exact magnitude of the upper temperature limit to life (or the extent of biosphere when considering geothermal gradient), however, is still under debate.

(2) Fluid chemistry provides energetic substrates and cofactors to sustain microbial communities at high temperatures. Any potential metabolism has to meet the fundamental thermodynamic requirement with negative free energy yields driven by chemical disequilibrium. The overall bioenergetic budget would provide insights to the minimum energetic requirement for life, and the competition and collaboration among species.

(3) Despite limited lineages possessing known (hyper)thermophilic strains deposited in culture collection, numerous sequences have been detected in high temperature environments (such as Korarchaeota, Candidate division OP, phylotypes BH1 and EM19) without further information about their physiological characteristics, making the inference of possible metabolisms for these uncultured phylotypes and their roles in ecosystems very challenging.

(4) The cataloguing of 16S rRNA gene sequences could provide bases to investigate the mechanisms that shape the overall diversity patterns in hydrothermal ecosystems. Most of what we know about the origin, maintenance, and distribution of biodiversity stems from research on plants and animals. Whether biogeographic isolation or dispersion observed for plants and animals is universally applicable to microorganisms and whether diversity patterns are influenced by other factors such as spatial scale, spatial heterogeneity, and energy availability warrants further investigations.

    While complete characterization of hydrothermal ecosystems would be merited with employing approaches inherited from multiple disciplines, merging geological and biological strengths would offer great insights into how microorganisms can survive and function in extremely hot environments that represent the consequences of interaction between subsurface and surface processes. We, therefore, launched a three-year research program (starting from August of 2006) that incorporates various expertises, including geochemistry (L.H. Lin and P.L. Wang of NTU), microbiology (C.Y. Chen and H.C. Ho of TCU), population genetics (H.T. Yu of NTU) and ecology (Y.T. Lin of NTU), in an attempt to achieve the identification of fluid reservoirs and circulative pathways, and community structures and their expressional functions in various hydrothermal environments across Taiwan.

最後更新 ( 2007/09/10, 週一 )