Proposal title: the effects of nitrogen form and concentration on toxin phenotypes of microcystis like many lakes worldwide, the western basin of lake erie experiences recurring, annual blooms of…

The University of Tennessee received a $746,743 Cooperative Agreement from the National Oceanic and Atmospheric Administration (NOAA) under the Center for Sponsored Coastal Ocean Research Coastal Ocean Program (CFDA 11.478), effective June 1, 2025, through May 31, 2028. This three-year research award funds scientific investigation into the environmental and physiological mechanisms controlling microcystin toxin production in Microcystis aeruginosa, a cyanobacterium responsible for recurring harmful algal blooms in Lake Erie's western basin. The research addresses critical knowledge gaps regarding how nitrogen availability and form influence toxin phenotypes at the cellular and strain levels, with the ultimate objective of developing improved quantitative predictive models for toxin content forecasting to support ecosystem management and drinking water security.

The deliverables from this research include comprehensive characterization of 10 or more Microcystis strains to elucidate the genomic, regulatory, and metabolic mechanisms underlying variable toxin responses to nitrogen availability—phenotypes currently undescribed in scientific literature. Research outcomes will contribute actionable science to NOAA's broader mission of supporting coastal ecosystem protection and public health by enhancing the scientific foundation for bloom toxicity prediction and management strategies in Lake Erie and comparable freshwater systems experiencing cyanobacterial blooms.

Proposal title: the effects of nitrogen form and concentration on toxin phenotypes of microcystis like many lakes worldwide, the western basin of lake erie experiences recurring, annual blooms of cyanobacteria dominated by microcystis, a notorious producer of the cyanotoxin microcystin. Microcystin represents a significant threat to ecosystem function, drinking water security, and human health. As such, intensive research has focused on the environmental and physiological cues that stimulate microcystin biosynthesis. In addition, an ability to quantitatively predict trends microcystin production in lake erie (and other lakes) is needed. Essential to the task of forecasting toxin content at a temporal and spatial resolution needed by stewards of lake erie, is a much-improved understanding of how environmental stimuli quantitatively influence microcystin production. Microcystin quota (amount of toxin in a cell) is highly plastic and is modified by environmental factors including nitrogen (N) availability. A widely accepted paradigm holds that microcystin increases with N. While typically true at bloom scale, this paradigm fails at the cellular and strain level. Preliminary data presented herein demonstrates that microcystin quota increases with N availability in some strains of microcystis, and decreases with N in other strains. These responses are an undescribed toxin phenotype in microcystis that likely underlie much of the inconsistency in laboratory and field studies of this organism. The genomic, regulatory, and metabolic mechanisms underpinning these phenotypes are unknown, as are their prevalence in nature. Yet, such phenotypes directly influence the toxigenicity of blooms and are an example of our ignorance about regulation of microcystin production. More importantly, these phenotypes represent a GAP in knowledge which must be bridged for models to better forecast quantitatively the toxin content of blooms. To close this GAP, 10+ strains of M. Aeruginosa will be screened for the opposing toxin phenotypes using nitrate gradients in continuous cultures. This will capture strain variability, estimate phenotype prevalence, and quantify microcystin production relative to N availability in each phenotype. Two or more strains of each phenotype will be further tested using gradients of urea and ammonium to determine consistency of the phenotypic responses to other forms of N. The genomic, transcriptomic, metabolomic, and photosynthetic features of one strain of each type will be extensively characterized to identify the mechanistic underpinnings of the toxin phenotypes. Results will be used to incorporate toxin phenotype parameters into an existing agent-based model that mechanistically predicts microcystin production based on physiological and environmental parameters. The updated model will be applied and validated in lake erie bloom populations in nutrient-amendment mesocosm studies.