Functional filtering and random processes affect the assembly of microbial communities of snow algae blooms at Maritime Antarctic

The increasing temperatures at the West Antarctic Peninsula (Maritime Antarctic) could lead to a higher occurrence of snow algal blooms which are ubiquitous events that change the snow coloration, reducing albedo and in turn exacerbating melting. However, there is a limited understanding of snow algae blooms biodiversity, composition, and their functional profiles, especially in one of the world's areas most affected by climate change. In this study we used 16S rRNA and 18S rRNA metabarcoding, and shotgun metagenomics to assess the diversity, composition, and functional potential of the snow algae blooms bacterial and eukaryotic communities at three different sites of Maritime Antarctic, between different colors of the algae blooms and between seasonal and semi-permanent snowfields. We tested the hypothesis that the functional potential of snow algae blooms is conserved despite a changing taxonomic composition. Furthermore, we determined taxonomic co-occurrence patterns of bacteria and eukaryotes and assessed the potential for the exchange of metabolites among bacterial taxa. Here, we tested the prediction that there are co-occurring taxa within snow algae whose biotic interactions are marked by the exchange of metabolites. Our results show that the composition of snow algae blooms vary significantly among sites. For instance, a higher abundance of fungi and protists were detected in Fildes Peninsula compared with Doumer Island and O'Higgins. Likewise, the composition varied between snow colors and snow types. However, the functional potential varied only among sampling sites with a higher abundance of genes involved in tolerance to environmental stress at O'Higgins. Co-occurrence patterns of dominant bacterial genera such as Pedobacter, Polaromonas, Flavobacterium and Hymenobacter were recorded, contrasting the absence of co-occurring patterns displayed by Chlamydomonadales algae with other eukaryotes. Finally, genome-scale metabolic models revealed that bacteria within snow algae blooms likely compete for resources instead of forming cooperative communities.