DISTRIBUTION AND ACTIVITY OF METHANOGENS AND HOMOACETOGENS IN DEEP GRANITIC AQUIFERS AT ASPO HARD-ROCK LABORATORY, SWEDEN

This study reveals the existence of active chemoautolithotrophic micro bial communities in deep granitic groundwater, containing hydrogen and methane. Homoacetogens and acetotrophic methanogens dominated in the groundwater down to a depth of 112 m, while autotrophic methanogens pr evailed deeper, down to 446 m. The results from most probable number c ounts showed that viable methanogens and homoacetogens coexisted at al l depths investigated, from 45 m to 446 m below sea level. In vitro ra diotracer experiments demonstrated these microorganisms to form methan e and acetate from CO2 with hydrogen, and methane from [C-14]acetate a t close to in situ temperature (17 degrees C). The data suggest that a utotrophic methanogens and homoacetogens initiate a deep subterranean food chain and that acetate-dependent methane formation is mediated by homoacetogenesis. The finding of an active, deep, hydrogen based auto trophic biosphere adds a significant but previously overlooked reducin g activity to deep granitic rock. (C) 1998 Published by Elsevier Scien ce B.V. All rights reserved.