Microbial communities in the brines of two Antarctic frozen lakes (Boulder Clay)

During a GPR survey, 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) with a different salinity (0.2 and 3.6 mS/cm, respectively) and pH (8.17 and 8.76, respectively). Brines were analyzed for bacterial diversity by Ion Torrent DNA and cDNA sequencing, microbial abundances (by image analysis and flow cytometry) and metabolic activities (by Biolog-Ecoplate(TM) and potential rates of ectoenzymatic activities determinations). The analysis of DNA sequences generally showed the predominance of Bacteroidetes, followed by Proteobacteria and Actinobacteria. The highest percentage (6.0 vs 1.7%) of active bacteria (by the analysis of RNA sequences; mainly Bacteroidetes) was observed in Lake-1. This latter harboured microbial populations characterized by higher prokaryotic cell abundances, volumes, biomass and virus abundance than Lake-2. Diverse cell morphotypes were observed in the two lakes. Different metabolic responses were also determined, with higher numbers of respiring cells and higher rates of ectoenzymatic activities, as well as the ability to better utilize carbon sources, in Lake-1 than in Lake-2. Results highlighted differences in the analyzed cryoenvironments in terms of diversity, abundance and metabolism, suggesting that Antarctic lakes might possess distinct microbial features in spite of their spatial proximity.