Microbial respiration in ice at subzero temperatures (-4°C to -33°C)

The habitability of icy environments may be limited by low temperature, low nutrient concentrations, high solute concentrations and the physical ice matrix. The basal ice of ice sheets and glaciers contains sediments that may be a source of nutrients for microbial activity. Here we quantify microbial respiration and active cell populations of Antarctic glacial isolates Paenisporosarcina sp. B5 and Chryseobacterium sp. V3519-10 in laboratory ices with abundant nutrients at temperatures from -4°C to -33°C. At all temperatures, initial high rates of metabolism were followed by lower rates suggestive of a non-reproductive metabolic state such as maintenance or dormancy. Metabolism was sustained by viable cells as quantified via culturability, CTC reduction and LIVE/DEAD staining. Respiration rates based on active cell populations did not correspond to rates representative of reproductive growth from the literature, but suggested lower levels of metabolism. Our data demonstrated that bacteria actively respired acetate in polycrystalline ice with abundant nutrients despite low temperatures and the physical ice matrix. Our results suggest that the debris-rich basal ice that exists at temperatures just below the freezing point and underlies portions of both the Greenland and Antarctic ice sheets represents a significant potential habitat for metabolically active microbial communities.