Comparative Metagenomic Analysis of Cryosol and Aquatic Microbiomes of the Larsemann Hills Oasis, East Antarctica

Using high-throughput sequencing of hypervariable regions of the 16S rRNA gene, a comparative analysis of the microbiomes of the active layer (on average, 95–100 cm) of psammozems (Oxyaquic Turbic Cryosols (Arenic)) and algal–bacterial communities of nearby water bodies was conducted. The study focused on the biodiversity of oxygenic phototrophic bacteria, which are the primary producers in most Antarctic ecosystems. The taxonomic and metabolic profiles of 20 samples representing a vertical spatial gradient of ecotopes—littoral algal–bacterial mats and two types of microbial communities (with and without surface algal–moss growths) in the organogenic horizons of psammozems—were analyzed. It was found that the core microbiomes of different types in the active layer are similar in their phylotaxonomic composition (Actinomycetota, Pseudomonadota, Bacteroidota, Cyanobacteriota, and Chloroflexota) but differ in species richness, which is higher in psammozems with an organogenic surface layer. Furthermore, the microbiomes of terrestrial algal–bacterial communities and the upper biogenic layers of cryogenic soils were characterized by pronounced biodiversity of oxygenic phototrophic bacteria (class Oxyphotobacteria), while in the underlying layers, nonphotosynthetic and potentially parasitic members of the Vampirovibrionophyceae class (phylum Cyanobacteriota) predominated. Moreover, both in the aquatic and soil microbiota, in the upper organo-accumulative layers with algal–bacterial and moss growths, filamentous non-heterocystous (order Leptolyngbyales) and heterocystous (order Nostocales) cyanobacteria were most frequently found; most of them inhabit the cryosphere of polar and subpolar regions. This study demonstrates, for the first time, the ability of filamentous cyanobacteria of the genus Phormidesmis, predominating in the algal–bacterial mats, to penetrate into the deep layers of psammozems and colonize various ecological niches in the amphibious Antarctic landscapes. The obtained data attest to the vertical stratification of the studied microbiomes reflected in the transition from photoautotrophic to chemoheterotrophic taxa among dominants in the upper horizons and in the prevalence of heterotrophic detrital metabolic strategies in the underlying soil horizons.