Predicting the global response of the glacier-fed streams and their bacterial microbiome to climate change

<p>&#160;</p><p>Glaciers are receding worldwide because of climate change, and as a consequence, glacier-fed streams are expected to undergo deep physical and chemical changes in the future, potentially inducing dramatic ecological shifts. At the base of glacier-fed stream ecosystems are bacteria, which, along with eukaryotic algae, form biofilms that drive biogeochemical transformations and fluxes of global relevance. Despite this importance, relatively little is known about the glacier-fed stream microbiome and even less on how it may be affected by climate change. The Vanishing Glaciers Project offers a novel and powerful opportunity to investigate this idea, with 16S rRNA amplicon data, shotgun metagenome sequencing, and physicochemical parameters assessed for glacier-fed streams distributed globally. Here, using data from 161 of the sampled streams, combined with glaciological modelling, we examined a) how the environmental template of these ecosystems will change according to several scenarios of climate change; b) how these changes will alter species distributions for the most prevalent bacterial community members; and c) how the ecological properties of abundant taxa vary along the gradient of glacier influence. We predict, that glacier-fed streams will undergo a process analogous to the &#8220;greening&#8221; of terrestrial alpine ecosystems, as benthic algal abundance is forecasted to significantly increase. Models based on 16s rRNA amplicon data predict the total bacterial abundance to greatly expand, but differences across taxa reveal unique responses to the modelled environmental changes. Corroborative evidence for shifts in bacterial communities along the gradient of glacier influence was found using metagenome assembled genomes, where we identified genomic features putatively adaptive to cryospheric conditions. Within these changes in taxa abundance, we highlight the shifting role of specialists within the community. Overall, this work sheds light on how bacteria adapt to the extreme environmental conditions of glacier-fed streams, and how climate change will impact these unique communities.</p>