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Beneath the glacier

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The frigid environment under glaciers is inhospitable to all but the most intrepid of microscopic life. To eke out a living, these microbes must do without sunlight and the photosynthetically fixed carbon that fuels most other ecosystems on Earth. Instead, such ecosystems are likely supported by chemosynthetic primary production that capitalizes on energy from inorganic reactions to produce biomass, but the exact mechanisms enabling such chemosynthetic life under the ice are unknown.

Eric Dunham, from Montana State University, USA, and colleagues collected sediments from a glacial system in Iceland that overlays a silicate mineral-rich basaltic catchment, conditions that are prevalent across glacial systems. High concentrations of the reductant hydrogen (H2) were detected, which likely formed when silicate minerals pulverized by the glacier reacted with water. In microcosms seeded with the sediments and amended with H2 and 14CO2, subglacial microbes could oxidize H2, using the resulting energy for chemosynthetic carbon fixation. Metagenomic sequencing from enrichment cultures revealed two prominent autotrophic hydrogenotroph populations, one likely restricted to H2-based chemoautotrophy and one with genomic potential for mixotrophy. The populations exhibited rates of H2 oxidation and carbon fixation approximately tenfold higher than those taken from a Canadian glacier overlying carbonate and shale, suggesting specialization to H2-rich conditions in basalt-glacier systems.

Credit: Natthawat/Getty Images

Interactions between glaciers and rock that can turn an otherwise inhospitable environment into a home for microbes could have implications beyond present-day Earth. Icy H2-dependent primary production could have sustained life during Snowball Earth episodes in our planet’s distant past, or could pave the way for life to evolve on Saturn’s frozen moon Enceladus.


Source: Ecology - nature.com

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