Towards a global biogeography of the glacier-fed stream benthic microbiome

Abstract Nearly 60% of the world’s glaciers are predicted to be lost by the end of the century because of global warming1. The impacts of this environmental change on the glacier-fed stream (GFS) ecosystems are profound, putting their ecological communities at risk2–4. Life in GFSs is dominated by benthic microbial biofilms, which regulate key ecosystem processes and form the basis of the food web5 . However, the biodiversity and biogeography of the biofilm microbiome of the world’s GFSs remain unknown, precluding a mechanistic understanding of its responses to glacier shrinkage. Here, applying metabarcoding to the benthic biofilm bacteria from 148 GFSs draining the world’s major mountain ranges, we unveil their global biodiversity and biogeography. We find that the global GFS benthic microbiome differs from other cryospheric microbiomes and is unexpectedly diverse. A large microbiome fraction (58% of the total amplicon sequence variants) is endemic to single mountain ranges, while 0.4% are disproportionately abundant and form a cosmopolitan core. These microbiome components have overlapping taxonomies, but their compositional turnover is differently shaped by dispersal limitation and environmental selection. Phylogenetic analyses relate prevalent clades to endemicity and microdiversity, the latter potentially buffering the GFS microbiome against climate-change impacts. Our global survey provides the basis for future climate-change microbiology studies6 on a rapidly changing ecosystem.