Diversity and metabolic profiles of prokaryotic communities in extra-terrestrial analogues on Earth: perennially ice-covered Antarctic lake brines

A number of polar environments encapsulate brine pools characterized by a unique combination of extreme conditions (mainly in terms of high salinity and low temperature). To explore the biodiversity and ecological role of prokaryotes in terrestrial cryosystems, brine pockets from three lakes in the Northern Victoria Land (lying in the Tarn Flat, TF, and Boulder Clay, BC, areas) were analysed by NGS (including the predictive functional analysis on 16S rRNA gene data), and the estimation of extracellular enzyme activities and microbial abundances. Differences in the analysed cryoenvironments were recorded in terms of prokaryotic diversity, abundance and retrieved metabolic pathways. By the analysis of DNA sequences, common operational taxonomic units were in the range 2.2-22.0%. The bacterial community was dominated by Bacteroidetes. In both BC and TF brines, sequences of the most thermally tolerant and methanogenic Archaea were detected, some of them related to well-known hyperthermophiles. The prediction analysis of the metabolic functions highlighted that the prokaryotic communities were involved in methane metabolism, biodegradation of aromatic compounds and carbon metabolism. The influence exerted by environmental parameters on the community composition and activities is discussed. Our findings indicate perennially ice-covered Antarctic lake brines as plausible terrestrial candidates for the study of the potential for extant life on different bodies of our solar system.