title: Nutrient-Controlled Niche Differentiation of Western Lake Erie Cyanobacterial Populations Revealed via Metatranscriptomic Surveys.
abstract: Although toxic cyanobacterial blooms in western Lake Erie threaten drinking water supplies and are promoted by nutrient loading, the precise nutrient regime that selects specific cyanobacteria populations is poorly understood. Here, we assess shifts in cyanobacterial abundances and global gene-expression patterns in response to natural and manipulated gradients in nitrogen and phosphorus to identify gene pathways that facilitate dominance by different cyanobacteria. Gradients in soluble reactive phosphorus shaped cyanobacterial communities and elicited the largest transcriptomic responses. Under high-P conditions (closest to the mouth of the Maumee River), Anabaena and Planktothrix were the dominant cyanobacterial populations, and experimental P and ammonium enrichment promoted nitrogen fixation gene (nifH) expression in Anabaena. For Microcystis, experimental additions of P up-regulated genes involved in phage defense, genomic rearrangement, and nitrogen acquisition but led to lower abundances. Within offshore, low-P regions of the western basin of Lake Erie, Microcystis up-regulated genes associated with P scavenging (pstSCAB, phoX) and dominated cyanobacterial communities. Experimental additions of ammonium and urea did not alter Microcystis abundances but did up-regulate protease inhibitors (aer and mcn gene sets) and microcystin synthetase genes (mcy), with urea enrichment yielding significant increases in microcystin concentrations. Our findings suggest that management plans that reduce P loads alone may not significantly reduce the risk of cyanobacterial blooms in western Lake Erie but rather may promote a shift among cyanobacterial populations (Microcystis, Anabaena, and Planktothrix) toward a greater dominance by toxic strains of Microcystis.
authors.affiliation: School of Marine and Atmospheric Sciences, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Harke
authors.affiliation: NOAA Great Lakes Environmental Research Laboratory , 4840 S. State Road, Ann Arbor, Michigan 48108, United States.
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Davis
authors.affiliation: Canadian Centre for Inland Waters, Environment Canada , Burlington, Ontario L7R 4A6, Canada.
authors.forename: Susan B
authors.initials: SB
authors.lastname: Watson
authors.affiliation: School of Marine and Atmospheric Sciences, Stony Brook University , Stony Brook, New York 11794, United States.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Gobler
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D000458:Cyanobacteria / Q000235:genetics / Q000502:physiology*; D017753:Ecosystem; D060106:Lakes / Q000382:microbiology; D009584:Nitrogen / Q000378:metabolism*; D009820:Ohio; D010758:Phosphorus / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D059467:Transcriptome
chemical_list: D001426:Bacterial Proteins; D010758:Phosphorus; D009584:Nitrogen