Subsurface ice as a microbial habitat

We determine the physicochemical habitat for microorganisms in subsurface terrestrial by quantitatively constraining the partitioning of bacteria and fluorescent beads (1–10 m) between the solid ice crystals and the water-filled veins and boundaries around ice crystals. We demonstrate experimentally that the partitioning of spherical within subsurface ice depends strongly on size but is largely independent of particle concentration. Although bacteria are shown consistently to partition to the , larger particles, which would include eukaryotic cells, become trapped in the crystals little potential for continued metabolism. We also calculate the expected concentrations soluble impurities in the veins for typical bulk concentrations found in natural . These calculations and scanning electron microscope observations demonstrate a concentrated environment (3.5 M total ions at 10 C) in the veins, where bacteria found to reside, with a mixture of impurities that could sustain metabolism. Our show that typical bacterial cells in glacial ice would fit within the narrow , which are a few micrometers across. These calculations are confirmed by microscopic of spherical, 1.9-m-diameter, fluorescent beads and stained bacteria in veins. Typical bacterial concentrations in clean ice (102–103 cells/mL) would in concentrations of 106–108 cells/mL of vein fluid, but occupy only a small fraction the total available vein volume (0.2%). Hence, bacterial populations are not limited vein volume, with the bulk of the vein being unoccupied and available to supply energy and nutrients.