# Experimental insights in taxon-specific functional responses to droughts in glacier-fed stream biofilms

## TL;DR

This study explores how glacier-fed stream biofilms respond to droughts, revealing shifts in microbial communities and functions.

## Contribution

The study provides new empirical insights into taxon-specific functional responses of glacier-fed stream biofilms to droughts using a multi-omics approach.

## Key findings

- Short-term droughts caused minor changes, including mild upregulation of heterotrophic metabolism and stress in diatoms.
- A longer drought shifted phototrophic dominance from diatoms to Cyanobacteriota and increased heterotrophic metabolism.
- A third drought had no detectable transcriptomic effect, suggesting adaptive responses in biofilm microorganisms.

## Abstract

Glacier-fed streams are predicted to face increasingly frequent and intense droughts. However, the impacts of drought events on benthic biofilm, including bacteria, eukaryotes, and viruses, the dominating life form in glacier-fed streams, remain poorly understood.

Using streamside flume mesocosms in the Swiss Alps, we grew glacier-fed stream biofilms over 103 days and exposed them to three droughts. Using a multi-omics approach (metagenomics, metatranscriptomics, and metaproteomics), we assessed the effects of a series of droughts on the taxonomy and metabolic activity of bacterial, eukaryotic, and viral metagenome-assembled genomes (MAGs). We found that the first drought (6 h) caused only minor changes, including mild upregulation of heterotrophic metabolism and signs of stress in diatoms. In contrast, the second drought (24 h) significantly altered both the composition and functionality of the microbiome, shifting phototrophic dominance from diatoms to Cyanobacteriota, while maintaining overall phototropic biomass and further upregulating the heterotrophic metabolism. Interestingly, a third 24 h drought had no detectable transcriptomic effect between pre- and post-drought conditions, suggesting a certain level of adaptive responses to droughts, but with the low diatom abundance being maintained.

These findings indicate that glacier-fed biofilm microorganisms initially resisted short-term drought, but a second longer drought caused important shifts in their community structure, activity, and function. Climate-induced increases in drought frequency or duration may therefore have a lasting impact on microbial ecosystem functioning in glacier-fed streams.

Video Abstract

Video Abstract

The online version contains supplementary material available at 10.1186/s40168-026-02336-6.