Transcriptomic Responses in the Bloom-Forming Cyanobacterium Microcystis Induced During Exposure to Zooplankton

The bloom-forming, toxic cyanobacterium synthesizes multiple secondary metabolites and has been shown to deter zooplankton grazing. However, the biochemical and/or molecular basis by which deters zooplankton remains unclear. This global transcriptomic study explored the response of to direct and indirect exposures to multiple densities of two cladoceran grazers, and Higher densities of both daphnids significantly reduced cell densities and elicited a stronger transcriptional response in While many putative grazer deterrence genes (encoding microcystin, aeruginosin, cyanopeptolin, and microviridin) were largely unaffected by zooplankton, transcripts for heat shock proteins () increased in abundance. Beyond metabolites and , large increases in the abundances of transcripts from photosynthetic processes were observed, evidencing energy acquisition pathways were stimulated by grazing. In addition, transcripts of genes associated with the production of extracellular polysaccharides and gas vesicles significantly increased in abundance. These genes have been associated with colony formation and may have been invoked to deter grazers. Collectively, this study demonstrates that daphnid grazers induce a significant transcriptomic response in , suggesting this cyanobacterium upregulates specific biochemical pathways to adapt to predation. This work explores the transcriptomic responses of following exposure to grazing by two cladocerans, and Contrary to previous hypotheses, did not employ putative grazing deterrent secondary metabolites in response to the cladocerans, suggesting they may have other roles within the cell, such as oxidative stress protection. The transcriptional metabolic signature during intense grazing was largely reflective of a growth and stress response, although increasing abundances of transcripts encoding extracellular polysaccharides and gas vesicles were potentially related to predator avoidance.