Cyanobacteria sustain microbial diversity and community stability in Tibetan glacial cryoconites.

Cyanobacteria play a key role in aggregating cryoconite granules on glacier surfaces, creating stable microhabitats that support diverse microbial communities, which influence glacier albedo and melting. However, their contribution to bacterial diversity and community stability is not well understood. This study explores their impact on bacterial diversity and interactions within three cryoconite-related environments: sediments and overlying water in cryoconite holes, and surface cryoconites across four Tibetan glaciers. Our study revealed that Cyanobacteria contributed the most (15-21%) to the differences in community compositions between these three habitats within each glacier. Cyanobacteria were abundant only in cryoconite sediments and surface cryoconites, accounting for 31-37% and 12-38% of all sequences, respectively, and contributing 6-10% and 5-9% to bacterial richness. Cyanobacteria genera such as Chamaesiphon and Pseudanabaena were key taxa, interacting closely with Bacteroidetes genera (e.g., Flavobacterium and Ferruginibacter) and Proteobacteria genera (e.g., Rhodoferax and Polaromonas). Metabolic analysis suggests that Cyanobacteria may provide essential nutrients to their heterotrophic bacterial partners through carbon and nitrogen fixation. The collaboration between Cyanobacteria and these bacteria contributes to community stability. These findings suggest that Cyanobacteria may act as 'engineer taxa', influencing bacterial diversity and the structural-functional stability of cryoconite microbial communities, and providing new insights into the potential responses of glacier ecosystems to climate change.