Transcriptionally active nitrogen fixation and biosynthesis of diverse secondary metabolites by Dolichospermum and Aphanizominom-like Cyanobacteria in western Lake Erie Microcystis blooms

Cyanobacterial harmful algal blooms (cyanoHABs) in the western basin of Lake Erie are dominated by microcystin producing Microcystis spp., but other cyanobacterial taxa that coexist in these communities may play important roles in production of toxins and shaping bloom dynamics and community function. In this study, we used metagenomic and metatranscriptomic data from the 2014 western Lake Erie cyanoHAB to explore the genetic diversity and biosynthetic potential of cyanobacteria belonging to the Anabaena, Dolichospermum, Aphanizomenon (ADA) clade. We reconstructed two near-complete metagenome-assembled genomes from two distinct ADA clade species, each containing biosynthetic gene clusters that encode novel and known secondary metabolites that were transcriptionally active. These taxa also appear to have varying nutrient acquisition strategies, and their ability to fix N may be important for synthesizing N rich metabolites as well as supporting bloom persistence. Although not the dominant organism in this system, these results suggest that ADA may be important community members in western Lake Erie cyanoHABs that have the potential to produce unmonitored toxins. Highlights Through metagenomic approaches, we generated two near-complete metagenome assembled genomes from two distinct species that are dispersed across the ADA clade of cyanobacteria. These ADA cyanobacteria have the potential to produce a variety of known and novel secondary metabolites, and use different nitrogen fixation strategies as observed through differential transcript abundance This works highlights the diversity of cyanobacteria in western Lake Erie blooms despite their continued dominance by Microcystis , and that these less abundant cyanobacteria may produce unmonitored toxins and shape bloom dynamics through N-fixation.