Prokaryotic abundance, biomass and metabolism in the brines of an Antarctic perennially frozen lake (Tarn Flat, Northern Victoria Land).

The recent discovery on Mars of the possible presence of seasonal brines has increased interest in analogous environments on Earth. In fact, the ice cap of several Antarctic lakes encapsulates sometimes brine pools characterized by a unique combination of extreme conditions. Moreover, the study of these cryoecosystems allows insights on geochemical processes affecting the microbial life and on how the latter can be supported in similar terrestrial environments and in other icy worlds of the universe. In order to find new extreme ecological niches of life, in the framework of Italian National Research Programme in Antarctica (PNRA), in October-November 2014 a screening of several frozen lakes in the Northern Victoria Land through the ground probing radar (GPR) investigation was made. Two hypersaline brines found at two different depths (B1-3.90 m; B2-4.50 m) in a perennially frozen Turn Flat lake were studied. The two pockets of liquid brines were separated from an ice layer of 12 cm and had a different salinity (84-92 and 74-75 psu respectively) and pH (7.22 and 6.74 respectively). Brines were sampled under sterile conditions and analysed by microscopic image-analysis to assess abundance, cell-shape, viable (Live/Dead) and respiring cells (5-Cyano-2,3-ditolyl-tetrazolium chloride stain). Moreover, the physiological profiles by Biolog-Ecoplate(TM) were determined as well as the potential ectoenzymatic activities rates (leucine-aminopeptidase, LAP; ß-glucosidase, ?-GLU; alkaline-phosphatase, AP).