125 Evidence for Long-Term Survival of Microorganisms and Preservation of DNA

Tuesday, 24 October 2006
8:00 AM - 12:00 PM

EXTREMELY SLOW GROWTH OF SULFATE REDUCING BACTERIA IN DEEP SUBSURFACE ROCKS

Paper number: 125-2
Program: Technical Sessions
Time: 8:10 AM – 8:30 AM

Authors

Abstract

The spatial distribution and metabolic activity rate of extremely small sulfate reducing bacteria (SRB) inhabiting low porosity quartzite rock cores from ~1.8km below land surface within the Witwatersrand Basin, South Africa, was determined by microautoradiography. A dry reef intersection was sampled and a succession series of cores approaching a moderately thermophilic, fluid-filled fissure were also studied, utilizing two different tracers for contamination controls. Negative controls showed little or no sulfate reduction activity in the pristine inner portions of freshly pared core-faces. Evidence for activity of SRB was observed from both sampling locations, with positive results yielding millimeter-scale ‘hotspots' of trapped radioactive sulfide on silver foils. Colony morphology of the SRB responsible for hotspot formation was determined by scanning electron microscopy (SEM) with an associated electron dispersive X-ray (EDX) on the core-face. Isolated microcolonies (~40µm diameter) of extremely small rod-shaped microorganisms and associated filamentous organic matter were observed. Cell volumes were calculated to be on the order of 1.4x10-3µm3, barely within the lower limits necessary to harbor DNA. The intensity of silver foil hotspots was measured and correlated to a per cell metabolic activity rate: an average rate of 23 fmolsulfide cell-1 day-1 was calculated. This slow rate of growth implies an in situ state of senescence or maintenance metabolism.