To search for extraterrestrial life surrogate extreme environments on Earth have been chosen for
investigation. An example of a surrogate site is the Canadian subpermafrost. Investigations into microbial
communities occurred by access fracture borehole water in the Lupin gold mine, and drill rock cores and
drilling waters in the High Lake region of Nunavut, Canada. Membrane lipid analyses uses GC/MS and
HPLC/ES/MS/MS to provide estimates of biomass, phospholipid (PLFA) and respiratory quinone
composition, and compositional changes related to membrane stress caused by nutritional limitations or
exposure to toxic conditions. Lupin fracture borehole waters were collected from 800 to 1200 meters,
while the High Lake rock cores were collected from 335 to 535 meters. Biomass estimates based on PLFA
ranged from 0.25 to 22 pmol L-1 for the Lupin waters. High Lake drill waters had biomass that ranged
from below detection limits (bdl) to 595 pmol/ml, while rock core samples had biomass estimates ranging
from bdl to 32 pmol g-1. PLFA profiles revealed the presence of both Gram +/- bacteria and sulfatereducing
bacteria. Specific PLFA ratios indicate that the bacterial communities were physiologically
stressed. Menaquinones were the most abundant but varied in the dominant isoprene units between the two
sites. Ubiquinone to menaquinone ratio indicated that these samples have been anoxic for a long time.
Methods to detect life signatures at surrogate sites on Earth will be critical for assessing extraterrestrial life.
Currently, the membrane lipid analyses provide additional information not easily provided by other
molecular techniques.
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.
Conference Committee Involvement (2)
Instruments, Methods, and Missions for Astrobiology XI
12 August 2008 | San Diego, California, United States
Instruments, Methods, and Missions for Astrobiology X
28 August 2007 | San Diego, California, United States
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