GEOMICROBIOLOGY OF COLD HYPERSALINE SPRINGS

Stable hypersaline springs have formed along the western shore of Lake Winnipegosis, Manitoba, Canada, near the center of the North American continent. These modern springs are the result of a reversal of fluid flow of subglacial meltwater in the Western Canada Sedimentary Basin, following the retreat of glaciers, isostatic rebound, and the drainage of the giant Lake Agassiz. The brine springs discharge from the eastern edge of the Phanerozoic Williston Basin, from Devonian carbonates. The springs are all dominated by Na-Cl, and stable isotope analysis indicates a meteoric water origin. Dissolved sulfate was typically around 18 per mil, consistent with Middle Devonian Evaporites. Sediments in discharge pools are dominantly carbonates, with quartz, halite, and goethite as highly variable but significant components.

The saline discharges generate what is essentially a marine ecosystem, and at the highest salt concentrations (total dissolved solids 42 – 65 g/l) the springs support extensive growths of colorful microbial mats. These mats are dominated by a marine alga (Percursaria percursa), but include a wide variety of microbes, including cyanobacteria, sulfate-reducing bacteria, and methanogens. Environmental conditions and the geochemistry of the water, including temperature (5-30°C), pH (6.0-8.4), chloride (2 – 36 g/l), and iron (<0.1 - 2.7 mg/l) content, affect the spatial distribution of the mat communities and the activities of different functional groups of microbes. For example, methanogenesis potential was affected by salinity and availability of substrates for autotrophic or methylotrophic growth. Analysis of the communities by a variety of techniques including microscopy, culturing, fatty acid methyl ester and lipid biomarker analyses, and genetic techniques (amplified ribosomal DNA restriction analysis (ARDRA)) reveals a diverse community of Bacteria and Archaea. Physiological adaptations to these cold, saline environments, and implications for survival in extreme environments on Earth and on extraterrestrial bodies like Mars will be discussed.