Two microbial assemblages in lake brine pockets separated by a thick ice layer

Two distinct hypersaline brine pockets (TF4 and TF5) separated by a 12 cm-thick ice layer were sampled from Tarn Flat, an unexplored Antarctic perennially frozen lake. Samples were analyzed for prokaryotic (Bacteria and Archaea) diversity (Ion Torrent sequencing), microbial abundances (image analysis and flow cytometry) and metabolic activities (Biolog-Ecoplate(TM) and potential rates of ectoenzymatic activities). The two sites shared only 22 and 18% of OTUs for Bacteria and Archaea, respectively. Shannon diversity for archaeal and bacterial communities was higher in TF5 than TF4 (p value < 0.001). Both bacterial communities were dominated by Proteobacteria, followed by Bacteroidetes and Actinobacteria. The Archaeal community was mainly constituted by Euryarchaeota and Crenarchaeota. Prokaryotic and virus-like particle abundances were in the order of 109 cells/l and 1010 VLP/l, respectively, in both samples, with slightly higher counts in TF4 than TF5. However, the VLP/PA ratio was 2.7 times higher in TF4 than in TF5. Larger cells were detected in TF5 (0.105 µm3) than TF4 (<0.06 µm3) as well as higher values of physiological diversity, substrate richness, substrate evenness and equitability were determined in TF5 than TF4. The prokaryotic community hydrolyzed proteins rather than organic phosphates, and polysaccharide degradation was negligible in TF5 and high in TF4. Overall data revealed the occurrence of highly different microbial assemblages in the studied brines.