Abundant dissolved genetic material in Arctic sea ice Part I: Extracellular DNA

The porous medium of sea ice, a surface-rich environment characterized by low temperature and high salinity, has been proposed as a favorable site for horizontal gene transfer, but few measurements are available to assess the possibility of this mode of evolution in ice. Here, we report the first measurements of dissolved DNA in sea ice, measured by fluorescent dye staining of centrifugal-filter-concentrated samples of melted ice. Newly formed landfast and pack ice on the Canadian Arctic Shelf (ca. 71°N, 125°W) contained higher concentrations (scaled to volume of brine) of the major components of dissolved DNA—extracellular DNA and viruses—than the underlying seawater. Dissolved DNA was dominated by extracellular DNA in surface seawater (up to 95%), with viruses making up relatively larger fractions at depths below 100 m (up to 27%) and in thick sea ice (66–78 cm; up to 100%). Extracellular DNA was heterogeneously distributed, with concentrations up to 135 μg DNA L⁻¹ brine detected in landfast sea ice, higher than previously reported from any marine environment. Additionally, extracellular DNA was significantly highly enriched at the base of ice of medium thickness (33–37 cm), suggestive of in situ production. Relative to underlying seawater, higher concentrations of extracellular DNA, viruses, and bacteria, and the availability of numerous surfaces for attachment within the ice matrix suggest that sea ice may be a hotspot for HGT in the marine environment.