Viral and bacterial ecogenomics in globally expanding red snow blooms

Chlamydomonas algal blooms give snowmelt a red color, reducing snow albedo and creating a runaway effect that accelerates snow melting. The occurrence of red snow is predicted to grow in polar and subpolar regions with increasing global temperatures. Here, a global metaanalysis of microbial abundances showed that red snow had higher microbial abundances than white snow. We hypothesize that the increased microbial densities affect virus-bacteria interactions in snow, with potential effects on snowmelt dynamics. A genomic analysis of viral and bacterial communities in red and white snow from the Whistler region of British Columbia, Canada, identified 792 putative viruses infecting bacteria. The most abundant putative snow viruses displayed low genomic similarity with known viruses. We recovered the complete circular genomes of nine putative viruses, two of which were classified as temperate. Genomes of putative snow viruses encoded genes involved in energy metabolisms, such as NAD+ synthesis and salvage pathways. In model phages, these genes facilitate increased viral particle production and lysis rates. Yet, the frequency of temperate phages was positively correlated with microbial abundance in the snow samples. These results suggest the increased significance of temperate virus-bacteria interactions as microbial densities increase during snowmelt. We propose that this virus-bacteria dynamic may facilitate the red snow algae growth stimulated by bacteria, representing a potential biological feedback on snowmelt rates. ### Competing Interest Statement The authors have declared no competing interest.