A novel approach for cryobiome functional analysis with metaproteomics

Algal blooms occur during the summer melt on the Greenland Ice Sheet and on other melting supraglacial environments globally. Snow habitats are mostly inhabited by chlorophytes (Chlorophyceae and Trebouxiophyceae), while bare ice is dominated by streptophytes (Zygnematophyceae). These eukaryotes thrive at low temperatures and under high light and low nutrients, and they have specialised cellular mechanisms allowing for life under extreme conditions. However, little empirical data exists about the cellular adaptations of snow and glacial ice algae under these conditions, despite our growing knowledge of species diversity and associated abiotic conditions. We address this knowledge gap by identifying protein groups essential for the maintenance of cellular homeostasis under relevant environmental conditions from samples rich in snow and glacial ice algae from the Greenland Ice Sheet. Samples collected during summer algal blooms were subjected to a metaproteomics workflow using an established protein extraction protocol and LC-MS/MS analysis. Proteins were identified using a predicted protein database built from RNA sequencing data comprising of sequences from algae, but also other microorganisms present in the community such as bacteria and fungi. We assigned 35% of the recorded MS2 spectra to predominantly algal proteins, as well as bacterial and fungal proteins, corresponding to more than 5800 protein groups. This large dataset provides a starting point for dissecting cellular functions of cryogenic algae in these environments and allows us, for example, to evaluate the relative abundance of proteins linked to specific cellular pathways such as photosynthesis or lipid metabolism.