Diversity and assembling processes of bacterial communities in cryoconite holes of a Karakoram glacier

Cryoconite holes are small ponds that form on the surface of glaciers that contain a dark debris, the cryoconite, at the bottom and host active ecological communities. Differences in the structure of bacterial communities have been documented among Arctic and mountain glaciers, and among glaciers in different areas of the world. In this study we investigate the structure of bacterial communities of cryoconite holes of Baltoro Glacier, a large (62 km in length and 524 km2 of surface) glacier of the Karakoram, by high throughput sequencing of the V5-V6 hypervariable regions of the 16S rRNA gene. We found that Betaproteobacteria, dominated bacterial communities, with large abundance of genera Polaromonas, probably thanks to the highly versatile metabolism of this genus, and Limnohabitans, which may have been favoured by the presence of supraglacial lakes in the area where we sampled cryoconites. In addition, cryoconites that occurred in separate areas on the surface of the glacier hosted different bacterial communities, while no spatial pattern of variation in community structure was observed within each area. This probably occurred because of variation in environmental conditions, mainly pH, of cryoconite holes in different areas of the glacier surface.