Photophysiological Effects of Dichlorogramine on Harmful Algal Bloom-Forming Cyanobacteria
Phoebe Tong, Marie Spehlmann
Department of Biology
Faculty Supervisor: Zheng-Hui He
Harmful algal blooms (HABs) are ecologically disruptive events, often driven by excessive nitrogen and phosphorus in marine and freshwater systems. The bloom-forming cyanobacterium, Microcystis aeruginosa, is especially concerning due to its production of microcystin toxins, which threaten human health, wildlife, and water-based recreation. Dichlorogramine (DCG), derived from aquatic plants, significantly inhibits M. aeruginosa growth; however, the environmental conditions that shape DCG’s physiological impacts remain unclear. Our RNA-seq experiments demonstrated that DCG affects the expression of genes in light and photosynthesis-associated pathways. We propose to test how light intensity modifies DCG-driven stress responses in M. aeruginosa. We hypothesize that high-light stress will increase carotenoid levels due to their photoprotective role, whereas low light will favor phycobilins to maximize light harvesting. We predict chlorophyll concentrations will be reduced in DCG-treated cultures regardless of light intensity. To test this hypothesis, we compared DCG dose treatments with low light (20 μmol m−2 s−1) versus high light (80 μmol m−2 s−1) conditions, and quantified growth and characterize changes in chlorophyll, phycobilin, and carotenoid levels to evaluate whether DCG-induced photosynthetic disruption is amplified or buffered by light. Our study aims to clarify how DCG interacts with environmental light exposures to shape bloom suppression outcomes and mitigate microcystin toxin.