Subsurface ice as a microbial habitat

first_imgWe determine the physicochemical habitat for microorganisms in subsurface terrestrialice 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 aroundindividual ice crystals. We demonstrate experimentally that the partitioning of sphericalparticles within subsurface ice depends strongly on size but is largely independent ofsource particle concentration. Although bacteria are shown consistently to partition to theveins, larger particles, which would include eukaryotic cells, become trapped in the crystalswith little potential for continued metabolism. We also calculate the expected concentrationsof soluble impurities in the veins for typical bulk concentrations found in naturalice. These calculations and scanning electron microscope observations demonstrate a concentratedchemical environment (3.5 M total ions at 10 C) in the veins, where bacteriawere found to reside, with a mixture of impurities that could sustain metabolism. Ourcalculations show that typical bacterial cells in glacial ice would fit within the narrowveins, which are a few micrometers across. These calculations are confirmed by microscopicimages of spherical, 1.9-m-diameter, fluorescent beads and stained bacteria insubsurface veins. Typical bacterial concentrations in clean ice (102–103 cells/mL) wouldresult in concentrations of 106–108 cells/mL of vein fluid, but occupy only a small fractionof the total available vein volume (0.2%). Hence, bacterial populations are not limitedby vein volume, with the bulk of the vein being unoccupied and available to supply energysources and nutrients.last_img

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