Novel sulfur-oxidizing streamers thriving in perennial cold saline springs of the Canadian high Arctic.

Summary The perennial springs at Gypsum Hill (GH) and Colour Peak (CP), situated at nearly 80°N on Axel Heiberg Island in the Canadian high Arctic, are one of the few known examples of cold springs in thick permafrost on Earth. The springs emanate from deep saline aqui- fers and discharge cold anoxic brines rich in both sulfide and sulfate. Grey-coloured microbial stream- ers form during the winter months in snow-covered regions of the GH spring run-off channels (-1.3°C to 6.9°C, ~7.5% NaCl, 0-20 p.p.m. dissolved sulfide, 1 p.p.m. dissolved oxygen) but disappear during the Arctic summer. Culture- and molecular-based analy- ses of the 16S rRNA gene (FISH, DGGE and clone libraries) indicated that the streamers were uniquely dominated by chemolithoautotrophic sulfur-oxidizing Thiomicrospira species. The streamers oxidized both sulfide and thiosulfate and fixed CO2 under in situ conditions and a Thiomicrospira strain isolated from the streamers also actively oxidized sulfide and thio- sulfate and fixed CO2 under cold, saline conditions. Overall, the snow-covered spring channels appear to represent a unique polar saline microhabitat that protects and allows Thiomicrospira streamers to form and flourish via chemolithoautrophic, phototrophic- independent metabolism in a high Arctic winter envi- ronment characterized by air temperatures commonly below -40°C and with an annual average air tempera- ture of -15°C. These results broaden our knowledge of the physical and chemical boundaries that define life on Earth and have astrobiological implications for the possibility of life existing under similar Martian conditions.