Supraglacial microbial communities from an isolated high mountain glacier in Türkiye

Abstract. The biodiversity of glaciers has been studied in polar regions and mountain ranges, yet isolated high mountain peaks covered by glaciers in temperate regions – islands of ice – are virtually unknown. These systems are particularly at risk of rapid change and disappearance as temperatures increase, thus understanding their biological diversity and the potential for organisms to survive as the landscape alters is time-critical. In this study, we assessed the community composition of a glacier surface in Türkiye, located on the extinct volcano Ağri Daği (Ararat Mountain). We collected samples of sediment (cryoconite) from water-filled depressions (cryoconite holes), then analysed samples through culturing, microscopy, metabarcoding (16S and 18S rDNA), metagenomics and metatranscriptomics. We cultured and identified 158 bacterial strains belonging to 11 genera (Cryobacterium, Polaromonas, Flavobacterium, Arthrobacter, Massilia, Devosia, Paeniroseomonas, Deinococcus, Glaciihabitans, Knoellia, and Rugamonas) and 41 species. Nine species of Cryobacterium, Flavobacterium and Knoellia did not grow above 10 °C, indicating particular vulnerability to climate warming. Amplicon-based community structure was dominated by Cyanobacteria, with the genus Tychonema particularly abundant, while cultured isolates represented only a small fraction of amplicon diversity but captured phenotypically diverse, cold adapted heterotrophs. Functional potential in metagenomes revealed that cyanobacteria dominated bacterial primary production, whereas other phyla specialized in nutrient scavenging, which was further apparent in metatranscriptomic analysis. Transcriptomic analysis demonstrated disproportionate dominance of Cyanobacterial transcripts across core metabolic pathways. Amplicon analysis of 18S rDNA and rRNA reads from metatranscriptomics showed that eukaryotes were active, with communities dominated by Ciliophora, while metazoan grazers identified in other cryoconite systems (such as tardigrades and rotifers) were not detected in either molecular data or microscopy, suggesting a simplified, protist-dominated food web. The combination of different microbiological and molecular approaches demonstrates that this rapidly changing glacier hosts cyanobacteria-dominated, bacterial–protist assemblages with absence of metazoan grazers, showing that isolated low latitude glaciers are a viable microbial habitat under threat.