TotalRNA sequencing reveals active community and functional dynamics on the surface of the Greenland Ice Sheet

The ablation area of the Greenland Ice Sheet (GrIS) is a biome driven by microbial activity. During the summer melt season, the weathering crust of the ice becomes a wet living skin dominated by eukaryotic glacier ice algae, particularly Ancylonema spp., which accelerate ice melt through their dark pigmentation. Cryoconite holes, formed by sediment melting into the weathering crust, also dominate the landscape of the ice surface. They are primarily inhabited by cyanobacteria as the main primary producers and also host a diverse community of bacterial, fungal and other microeukaryotic heterotrophs. This study investigates the active microbial communities and functionality of the weathering crust and cryoconites using Total RNA metatranscriptomics. With this approach, we describe the full diversity of ice surface microbial communities; assembling, annotating and analyzing jointly full-length 16S rRNA and 18S rRNA genes in addition to transcriptomes. We conducted a seasonal study over a 21-day period during the ablation season, sampling ice and cryoconite habitats. Samples were collected from five cryoconite holes and five 2-meter patches of the weathering crust ca 25km inland on the GrIS, near Ilulissat. Biomass from cryoconite holes and ice surfaces was collected at solar noon on seven sampling days during the summer. The findings highlight the dynamics and spatial variability of very different microbial communities between the weathering crust and cryoconite holes. Notably, the weathering crust is dominated by eukaryotic biomass, and spatial variability is significant; cryoconites are far more diverse, dominated by prokaryotic interactions and relatively stable temporally.  A snowfall in late summer provided a window of opportunity to show that cryoconites communities are robust, while the functionality of the weathering crust, including genes associated to carbon, nitrogen and phosphorus cycling all responded to snowfall. The Total RNA approach in this study provides a powerful insight into the entire active microbial community and their functionality on glacial surfaces.