RESUMO
Geochemical, microbiological, and molecular analyses of alkaline saline groundwater at 2.8 kilometers depth in Archaean metabasalt revealed a microbial biome dominated by a single phylotype affiliated with thermophilic sulfate reducers belonging to Firmicutes. These sulfate reducers were sustained by geologically produced sulfate and hydrogen at concentrations sufficient to maintain activities for millions of years with no apparent reliance on photosynthetically derived substrates.
Assuntos
Bactérias/isolamento & purificação , Bactérias/metabolismo , Ecossistema , Sulfatos/metabolismo , Microbiologia da Água , Bactérias/classificação , Biodiversidade , DNA Ribossômico/análise , DNA Ribossômico/genética , Ouro , Hidrogênio/análise , Hidrogênio/metabolismo , Mineração , Análise de Sequência com Séries de Oligonucleotídeos , Oxirredução , Filogenia , RNA Ribossômico 16S/genética , África do Sul , Temperatura , Termodinâmica , TempoRESUMO
Alkaline, sulfidic, 54 to 60 degrees C, 4 to 53 million-year-old meteoric water emanating from a borehole intersecting quartzite-hosted fractures >3.3 km beneath the surface supported a microbial community dominated by a bacterial species affiliated with Desulfotomaculum spp. and an archaeal species related to Methanobacterium spp. The geochemical homogeneity over the 650-m length of the borehole, the lack of dividing cells, and the absence of these microorganisms in mine service water support an indigenous origin for the microbial community. The coexistence of these two microorganisms is consistent with a limiting flux of inorganic carbon and SO4(2-) in the presence of high pH, high concentrations of H2 and CH4, and minimal free energy for autotrophic methanogenesis. Sulfide isotopic compositions were highly enriched, consistent with microbial SO4(2-) reduction under hydrologic isolation. An analogous microbial couple and similar abiogenic gas chemistry have been reported recently for hydrothermal carbonate vents of the Lost City near the Mid-Atlantic Ridge (D. S. Kelly et al., Science 307:1428-1434, 2005), suggesting that these features may be common to deep subsurface habitats (continental and marine) bearing this geochemical signature. The geochemical setting and microbial communities described here are notably different from microbial ecosystems reported for shallower continental subsurface environments.
