Papale M., Conte A., Azzaro M., Borruso L., Rizzo C., Spanò N.), La Ferla R., Guglielmin M., Lo Giudice A. Prokaryotic diversity (Bacteria and Archaea) in Antarctic hypersaline brines from a perennially frozen lake (Tarn Flat,Victoria Land)

Brine pockets inside permafrost remain liquid even when the temperature is well below freezing point. Two distinct hypersaline brine samples (at a depth of 390 and 450cm, namely TF4 and TF5, respectively) were collected from a perennially frozen lake in Tarn Flat (TF) through a borehole (51 mm diameter) in the centre of the frost mound using a semi-portable core auger1. Brine pockets were separated by a layer of ice having a thickness of 12cm. DNA was extracted from each sample (150 to 600ml), concentrated by filtering on 0.22 ?m-pore size polycarbonate membranes, and DNA library for Ion Torrent sequencing was prepared in triplicates by PCR using the engineered primers 27f and 338r. The sequencing process was provided with the Ion 314 chip. The raw data were analyzed using bioinformatics tools to determine the quality criteria of the reads. Differences of the prokaryotes communities between TF4 and TF5 were investigated via linear discriminant analysis effect size. Prokaryotic functionality was characterized using a functional inference-based (predicting functional profiles from metagenomics 16S rRNA, Tax4Fun) approach. The two sites shared only 22.2% and 18.5% of OTUs for Bacteria and Archaea, respectively. In both archaeal and bacterial communities Shannon diversity was higher in TF5 than TF4 (p value < 0.001). Both bacterial communities were dominated by Proteobacteria (65.9 and 41.1% in TF5 and TF4, respectively), followed by Bacteroidetes and Actinobacteria, whereas the Firmicutes, Spirochaetes and Planctomycetes were less abundant). Archaeal community was mainly constituted by Euryarchaeota (55.8 and 57.1% in TF4 and TF5, respectively), Crenarchaeota, and Ancient Archaeal Group, whereas Korarchaeota were less represented. Taxonomic diversity and functionality revealed the occurrence of highly different prokaryotic assemblages in the analyzed brine samples, even if they derived from the same lake. This finding could be related to their different physico-chemical features, as well asto their spatial separation.