Decrypting the phylogeny and metabolism of microbial dark matter in green and red Antarctic snow.

Antarctic snow harbors diverse microorganisms, including pigmented algae and bacteria, which create colored snow patches and influence global climate and biogeochemical cycles. However, the genomic diversity and metabolic potential of colored snow remain poorly understood. We conducted a genome-resolved study of microbiomes in colored snow from 13 patches (7 green and 6 red) on the Fildes Peninsula, Antarctica. Using metagenome assembly and binning, we reconstructed 223 metagenome-assembled genomes (MAGs), with 91% representing previously unexplored microbes. Green snow (GS) and red snow (RS) showed distinct MAGs profile, with Polaromonas and Ferruginibacter as the most abundant genera, respectively. GS exhibited higher alpha diversity with more unique and enriched MAGs, while RS showed greater variability with higher beta diversity. All MAGs contained genes encoding auxiliary activities (AAs), carbohydrate esterases (CEs), glycoside hydrolases (GHs), and glycosyl transferases (GTs), indicating microbial degradation of complex carbon substrates. The most abundant enzymes included GT2 (cellulose synthase), GT4 (sucrose synthase), CE1 (acetyl xylan esterase), GT41 (peptide beta-N-acetylglucosaminyltransferase), and CE10 (arylesterase). GS had a higher abundance of GTs, whereas RS was enriched in GHs. Furthermore, 56% of MAGs contained genes for inorganic nitrogen cycling, with 18 gene families involved in assimilatory nitrate reduction, dissimilatory nitrate reduction, and denitrification. Potential coupling of nitrogen cycling and carbohydrate metabolism was observed at both genome and community levels, suggesting close links between these pathways, particularly through nitrate reduction during carbohydrate degradation. This study enhances our understanding of microbial metabolic functions in polar ecosystems and highlights their roles in maintaining Antarctic ecological stability.