Abstract
Recent studies estimate that a half of living carbon in the earth may exist in subsurface environment. Deep subsurface microbial communities have recently received increased attention. There are strong but circumstantial indications of microbial life widespread at depth in the crust of the Earth. This communication presents preliminary information about the subsurface bacterial abundance. Abundances of total and selected bacteria in the interstitial water of granite and sedimentary rocks up to 1000 m deep were determined. Maximum abundance of 105～106 cells/ml was observed in the granite and sedimentary rock waters, respectively. Iron-oxidizing/reducing bacteria were detected at depths having specific pH and oxidation/reduction potential (Eh). Those pH and Eh regimes were corresponding to the Fe2+/Fe(OH)3 or FeS2/Fe2+, FeS2/FeCO3 interface conditions. It is implied that these bacteria are involved in geochemical processes such as precipitation, dissolution and cycling of sulfur, iron, and related elements.
