The diversity and biotechnological potentialities of bacterial isolates from brines of three Antarctic lakes of the Northern Victoria Land (namely Boulder Clay and Tarn Flat areas) were first explored. Cultivable bacterial communities were analysed mainly in terms of bacterial response to contaminants (i.e., antibiotics and heavy metals) and oxidation of contaminants (i.e., aliphatic and aromatic hydrocarbons and polychlorobiphenyls). Moreover, the biosynthesis of biomolecules (antibiotics, extracellular polymeric substances and enzymes) with applications for human health and environmental protection was assayed. A total of 74 and 141 isolates were retrieved from Boulder Clay and Tarn Flat brines, respectively. Based on 16S rRNA gene sequence similarities, bacterial isolates represented three phyla, namely Proteobacteria (i.e., Gamma- and Alphaproteobacteria), Bacteroidetes and Actinobacteria, with differences encountered among brines. At genus level, Rhodobacter, Pseudomonas, Psychrobacter and Leifsonia members were dominant. Results obtained from this study on the physiological and enzymatic features of cold-adapted isolates from Antarctic lake brines provide interesting prospects for possible applications in the biotechnological field through future targeted surveys. Finally, findings on contaminant occurrence and bacterial response suggest that bacteria might be used as bioindicators for tracking human footprints in these remote polar areas.

Two distinct pressurized hypersaline brine pockets (named TF4 and TF5), separated by a thin ice layer, were detected below an ice-sealed Antarctic lake. Prokaryotic (bacterial and archaeal) diversity, abundances (including virus-like particles) and metabolic profiles were investigated by an integrated approach, including traditional and new-generation methods. Although similar diversity indices were computed for both Bacteria and Archaea, distinct bacterial and archaeal assemblages were observed. Bacteroidetes and Gammaproteobacteria were more abundant in the shallowest brine pocket, TF4, and Deltaproteobacteria, mainly represented by versatile sulphate-reducing bacteria, dominated in the deepest, TF5. The detection of sulphate-reducing bacteria and methanogenic Archaea likely reflects the presence of a distinct synthrophic consortium in TF5. Surprisingly, members assigned to hyperthermophilic Crenarchaeota and Euryarchaeota were common to both brines, indicating that these cold habitats host the most thermally tolerant Archaea. The patterns of microbial communities were different, coherently with the observed microbiological diversity between TF4 and TF5 brines. Both the influence exerted by upward movement of saline brines from a sub-surface anoxic system and the possible occurrence of an ancient ice remnant from the Ross Ice Shelf were the likely main factors shaping the microbial communities.

The active prokaryotic communities proliferate in the ecosystems of the Antarctic Ocean, participating in biogeochemical cycles and supporting higher trophic levels. They are regulated by several environmental and ecological forcing, such as the characteristics of the water masses subjected to global warming and particulate organic matter (POM). During summer 2017, two polynyas in the Ross Sea were studied to evaluate key-microbiological parameters (the proteasic, glucosidasic, and phosphatasic activities, the microbial respiratory rates, the prokaryotic abundance and biomass) in relation to quantitative and qualitative characteristics of POM. Results showed significant differences in the epipelagic layer between two macro-areas (Terra Nova Bay and Ross Sea offshore area). Proteins and carbohydrates were metabolized rapidly in the offshore area (as shown by turnover times), due to high enzymatic activities in this zone, indicating fresh and labile organic compounds. The lower quality of POM in Terra Nova Bay, as shown by the higher refractory fraction, led to an increase in the turnover times of proteins and carbohydrates. Salinity was the physical constraint that played a major role in the distribution of POM and microbial activities in both areas.

The effects of climate change-induced ice melting on the microbial communities in different glacial-fed aquatic systems have been reported, but seasonal dynamics remain poorly investigated. In this study, the structural and functional traits of the aquatic microbial community were assessed along with the hydrological and biogeochemical variation patterns of the Arctic Pasvik River under riverine and brackish conditions at the beginning (May = Ice-melt (−)) and during the ice-melting season (July = Ice-melt (+)). The microbial abundance and morphometric analysis showed a spatial diversification between the riverine and brackish stations. Results highlighted different levels of microbial respiration and activities with different carbon and phosphorous utilization pathways, thus suggesting an active biogeochemical cycling along the river especially at the beginning of the ice-melting period. At Ice-melt (−), Gammaproteobacteria and Alphaproteobacteria were dominant in riverine and brackish stations, respectively. Conversely, at Ice-melt (+), the microbial community composition was more homogeneously distributed along the river (Gammaproteobacteria > Alphaproteobacteria > Bacteroidetes). Our findings provide evidence on how riverine microbial communities adapt and respond to seasonal ice melting in glacial-fed aquatic ecosystems.