Microbial activities in deep subsurface environments

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Abstract
Activities of microorganisms residing in terrestrial deep subsurface sediments were examined in 46 sediment samples from three boreholes. Radiolabeled time course experiments assessing in situ microbial activities were initiated within 30 min of core recovery. [1‐C4] Acetate incorporation into lipids, [ methyl‐3H] thymidine incorporation into DNA, [2‐14C]acetate, and [U‐14C]glucose mineralization in addition to microbial enrichment and enumeration studies were examined in surface and subsurface sediments. Surface soils contained the greatest biomass and activities, followed by the shallow aquifer zones. Water‐saturated subsurface sands exhibited three to four orders of magnitude greater activity and culturable microorganisms than the dense clay zones, which had low permeability. Regardless of depth, sediments that contained more than 20% clays exhibited the lowest activities and culturable microorganisms.