Microbial assemblage and metabolism in the brines of two Antarctic frozen lakes (Boulder Clay, Northern Victoria Land)

Frozen lakes are a prominent structure in the ice-free regions of Antarctica and such perennial glacial lakes sometimes encapsulate lenses of brines, representing an extreme cryogenic ecosystem. The study of these unique environments allows insights on the geochemical processes affecting the microbial life in analogues terrestrial cryoecosystems and increases our perceptions on possible traces of life that must be sought beyond Earth. In order to find new extreme refugia for microbial life, 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 lenses of liquid brines were found at different depths in two adjacent frozen Boulder Clay lakes (Lake-1: 2.5 m; Lake-2: 2.0) and had a different salinity (0.2 and 3.6 mS/cm, respectively) and pH (8.17 and 8.76, respectively). Brines were sampled under sterile conditions and analysed by microscopic image-analysis to assess prokaryotic abundance, cell-shape, and respiring cells (CTC+) and by flow-cytometry to determine virus abundance. 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).