Prokaryotic Communities in polar Brines: Ecological and Astrobiological Insights from Antarctica

Brine pockets embedded within Antarctic permafrost and subglacial environments represent natural laboratories for studying microbial life under polyextreme conditions—high salinity, sub-zero temperatures, and oligotrophy. These analogues to extraterrestrial environments, such as the sub-ice oceans of Europa or the briny regolith of Mars, are crucial to astrobiological investigations looking to define the limits of life. As part of the Italian National Research Programme in Antarctica (PNRA) in the framework of the CLICPERECO project, a structured sampling campaign was conducted in the Tarn Flat (TF) area of Northern Victoria Land, where multiple brine inclusions were discovered and sampled. Samples were collected from a triangular sampling grid with vertices TF1, TF2, and TFB, each 18 meters apart, and from a central point (TF3) at three depths: 380, 460, and 510 cm (TF3-380, TF3-460, TF3-510), along with a sediment sample at the lake bottom (SED-TF3). DNA was extracted using the DNeasy PowerSoil Kit, followed by 16S rRNA gene amplicon sequencing on the Illumina HiSeqX platform. Taxonomic assignment was performed using the SILVA 138.1 database. The prokaryotic community displayed substantial spatial and vertical heterogeneity. Across all samples, Actinomycetota, Bacteroidota, and Proteobacteria were the dominant phyla. In the triangular grid, Actinomycetota reached over 32% at TF1 and TFB, while Cyanobacteriota dominated TF2 (29.4%), suggesting influence from light exposure or surface dynamics. In the central borehole, clear depth-related stratification was observed. Actinomycetota decreased from 48.9% at TF3-380 to 14.6% at TF3-510, whereas anaerobic lineages like Thermodesulfobacteriota (from 0.02% to 4.3%) and Campylobacterota (up to 2.1%) increased with depth, indicating a shift toward more reduced conditions. At the genus level, “Candidatus Aquiluna” and Ilumatobacter dominated surface layers, while deep samples harbored sulfate reducers such as Desulfoconvexum, Desulfuromusa, and Geopsychrobacter. The genus Thiomicrorhabdus surged from <0.01% in surface layers to >11.6% at 460 cm, further indicating sulfur-driven metabolisms in deeper brines. The detection of high abundances of Patescibacteria (up to 7.5% at TF3-460), a superphylum comprising ultra-small, often symbiotic bacteria, suggests that deep brine ecosystems may support complex, syntrophic microbial interactions.

These findings highlight the presence of stratified, diverse microbial consortia finely tuned to microenvironmental gradients within analysed brines. The ecological novelty and functional potential of these communities extend the known boundaries of microbial life on Earth and offer compelling analogies for life detection strategies beyond our planet. Future work integrating metagenomics, metabolomics, and in situ geochemical measurements will be crucial to uncover the evolutionary and adaptive mechanisms underlying life in these cryo-habitats.