Community composition of cyanobacterial mats from the river Areuse (Switzerland)

Since the early 2000s, proliferations of benthic cyanobacteria producing derivatives of anatoxin-a have been reported in rivers worldwide. Here, we document such a toxigenic event happening in the river Areuse in Switzerland in 2020. We investigate the diversity and genomics of major bloom-forming riverine benthic cyanobacteria, and the associated heterotrophs. We show, using 16S rRNA-based community profiling, that benthic communities are dominated by Oscillatoriales, especially by Microcoleus species. Toxigenic mats harbor a distinct microbiome dominated by proteobacteria and bacteroidetes, which could support cyanonbacterial growth by providing them with essential vitamins. Overall, this study improves our understanding of the composition and dynamics of toxigenic benthic cyanobacterial blooms in rivers.