The diversity and abundance of chytrids on the Greenland Ice Sheet – new quantitative data

Zoosporic fungi of the Chytridiomycota phylum are lethal parasites of algae in Arctic freshwater and marine environments, and their presence has been confirmed as dominant fungi in various habitats on the Greenland Ice Sheet by amplicon sequencing. Glacier ice algae of the genus Ancylonema dominate microbial communities on the margins of the Greenland Ice Sheet and play key roles in darkening and melting of surface ice. Recent studies and in-situ observations have identified undescribed chytrids infecting Ancylonema spp. blooms, and their diversity and abundance were assessed by collection of ice surface and cryoconite holes samples from several locations on the ice sheet. We provide the first quantitative assessment, using qPCR, to reveal that uncultured chytridiomycetous fungi on dark ice were one order of magnitude higher than in cryoconites throughout the 2022 melt season on the Central-West margin of the Greenland Ice Sheet. Phylogenetic trees, based on the assembled environmental 18S rRNA genes, highlight that surface ice habitats dominated by glacier ice algae or snow algae harbor a great diversity of fungi belonging to the Blastocladiomycota, Monoblepharidomycota and Chytridiomycota phyla. They appear to be potential novel taxa, based on small subunit (18S) rRNA gene sequence similarity analysis, increasing our knowledge of chytrids diversity in Arctic environments. The number of novel lineages distinguished from described taxa varied from 63 to 81, respectively, based on two percentage of identity thresholds (> 97% and 98%). Overall, this study fills a significant knowledge gap on chytrids radiation in surface ice habitats of the Greenland Ice Sheet.