title: Transcriptomic Responses in the Bloom-Forming Cyanobacterium Microcystis Induced during Exposure to Zooplankton.
abstract: The bloom-forming, toxic cyanobacteriumMicrocystissynthesizes multiple secondary metabolites and has been shown to deter zooplankton grazing. However, the biochemical and/or molecular basis by whichMicrocystisdeters zooplankton remains unclear. This global transcriptomic study explored the response ofMicrocystisto direct and indirect exposures to multiple densities of two cladoceran grazers,Daphnia pulexandD. magnaHigher densities of both daphnids significantly reducedMicrocystiscell densities and elicited a stronger transcriptional response inMicrocystisWhile many putative grazer deterrence genes (encoding microcystin, aeruginosin, cyanopeptolin, and microviridin) were largely unaffected by zooplankton, transcripts for heat shock proteins (hsp) increased in abundance. Beyond metabolites andhsp, 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 inMicrocystis, suggesting this cyanobacterium upregulates specific biochemical pathways to adapt to predation.IMPORTANCEThis work explores the transcriptomic responses ofMicrocystis aeruginosafollowing exposure to grazing by two cladocerans,Daphnia magnaandD. pulexContrary to previous hypotheses,Microcystisdid 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.
authors.affiliation: Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Harke
authors.affiliation: Stony Brook University, School of Marine and Atmospheric Sciences, Southampton, New York, USA.
authors.forename: Jennifer G
authors.initials: JG
authors.lastname: Jankowiak
authors.affiliation: Stony Brook University, School of Marine and Atmospheric Sciences, Southampton, New York, USA.
authors.forename: Brooke K
authors.initials: BK
authors.lastname: Morrell
authors.affiliation: Stony Brook University, School of Marine and Atmospheric Sciences, Southampton, New York, USA christopher.gobler@stonybrook.edu.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Gobler
mesh_terms: D000818:Animals; D003621:Daphnia / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D047630:Depsipeptides; D015964:Gene Expression Regulation, Bacterial; D006360:Heat-Shock Proteins; D052998:Microcystins; D046931:Microcystis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism / Q000502:physiology*; D009842:Oligopeptides; D010456:Peptides, Cyclic; D010788:Photosynthesis; D012329:RNA, Bacterial; D064210:Secondary Metabolism / Q000235:genetics; D059467:Transcriptome / Q000502:physiology*; D015048:Zooplankton / Q000254:growth & development / Q000502:physiology*
chemical_list: D047630:Depsipeptides; D006360:Heat-Shock Proteins; D052998:Microcystins; D009842:Oligopeptides; D010456:Peptides, Cyclic; D012329:RNA, Bacterial; C078588:microcystin
keywords: RNA-Seq; grazing; microcystis; transcriptome