Algae-dominated metaproteomes uncover cellular adaptations to life on the Greenland Ice Sheet.

Eukaryotic algae-dominated microbiomes thrive on the Greenland Ice Sheet (GrIS) in harsh environmental conditions, including low temperatures, high light, and low nutrient availability. Chlorophyte algae bloom on snow, while streptophyte algae dominate bare ice surfaces. Empirical data about the cellular mechanisms responsible for their survival in these extreme conditions are scarce. This knowledge gap was addressed by quantifying proteins for both algal taxa from samples on the southern margin of the GrIS. We show that the streptophyte glacier ice algae have a relative enrichment in proteins involved in environmental signaling and nutrient transport, indicative of cellular readiness to dynamically respond to extreme GriS environmental cues, linked, for example, to photoprotection and the rapid update of scarce nutrients. In contrast, the chlorophyte snow algae have a high abundance of proteins linked to lipid and nitrogen metabolisms, providing evidence for the biological processes sustaining the cellular carbon and nitrogen stores necessary for survival in an oligotrophic environment. We also identify proteins in both taxa linked to the synthesis and breakdown of key cellular pigments. Our study gives novel insights into the cellular biology of these algae and their adaptation to extreme environments.