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Proceedings Paper

Microbial life in the unsaturated subsurface under conditions of extremely low recharge: an extreme environment
Author(s): Fred J. Brockman; Christopher J. Murray; Ellyn M. Murphy; Bruce Bjornstad; David Balkwill; David B. Ringelberg; Susan Pfiffner; Robert Griffiths
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Paper Abstract

Deep unsaturated sediments with very low levels of sediment- associated nutrients and extremely low levels of vertical movement of moisture (i.e., recharge) were studied as a model extreme environment to better understand microbial survival over geologic time periods and the resulting spatial distribution of viable microorganisms. Chloride mass balance measurements indicate that the study site has received an average annual recharge of 15 micrometers since the last Pleistocene flood approximately 13,000 years ago. Viable biomass as determined by measurement of phospholipid fatty acid in 75 g samples was approximately 104 cells/g sediment. However, highly sensitive microbial activity assays failed to detect microbial activity in > 60% of 10 g samples. Microbial activity was not detected in 29% of replicate 10 g samples in the presence of nutrients for 244 days, indicating that viable microorganisms are spatially discontinuous. In separate experiments, microbial activity was not detected in 0.1 g or 1 g samples but was encountered in 37% of the 10 g samples and in 75% of the 100 g samples. These results indicate that viable microorganisms exist in `hotspots' separated by extensive regions of excluding conditions. In addition, the results suggest that if extremely low nutrient flux conditions exist at target extraterrestrial locations, successful recovery of viable microorganisms may require acquisition of many, or large, samples.

Paper Details

Date Published: 11 July 1997
PDF: 7 pages
Proc. SPIE 3111, Instruments, Methods, and Missions for the Investigation of Extraterrestrial Microorganisms, (11 July 1997); doi: 10.1117/12.278793
Show Author Affiliations
Fred J. Brockman, Pacific Northwest National Lab. (United States)
Christopher J. Murray, Pacific Northwest National Lab. (United States)
Ellyn M. Murphy, Pacific Northwest National Lab. (United States)
Bruce Bjornstad, Pacific Northwest National Lab. (United States)
David Balkwill, Florida State Univ. (United States)
David B. Ringelberg, Univ. of Tennessee/Knoxville (United States)
Susan Pfiffner, Univ. of Tennessee/Knoxville (United States)
Robert Griffiths, Oregon State Univ. (United States)


Published in SPIE Proceedings Vol. 3111:
Instruments, Methods, and Missions for the Investigation of Extraterrestrial Microorganisms
Richard B. Hoover, Editor(s)

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