Physiological response of Microcystis aeruginosa exposed to aqueous extracts of Pistia stratiotes and Pontederia crassipes

Macrophyte extracts inhibit cyanobacteria growth, offering a sustainable solution for bloom control. The present study aimed to evaluate Microcystis aeruginosa’s response to aqueous extracts obtained from the dried biomass of Pistia stratiotes L. and Pontederia crassipes Mart. Solms. Physiological parameters analyzed included growth, photosynthesis, and antioxidative response. Reactive oxygen species generation and the chemical profile of the aqueous extracts were analyzed. At 4.0 g L ^-1 , both extracts inhibited cyanobacterial growth in 6 days. P. stratiotes extract achieved 100% inhibition, while P. crassipes extract reached 60%. P. stratiotes extract showed higher photosynthetic inhibition (99% vs. 12% for P. crassipes ). This was related to the downregulation of the psbA gene (coding for the photosystem II protein D1). Exposure to both extracts increased intracellular reactive oxygen species content in cyanobacterial cells and increased peroxiredoxin gene ( prxA) transcripts. This response was not noted for sod (superoxide dismutase) transcripts, although SOD enzymatic activity increased in cultures exposed to P. stratiotes extracts. Upon incubation of the macrophyte extracts with M. aeruginosa cultures, phenol concentrations decreased, and their general metabolic profile changed. Thus, P. stratiotes extract outperformed P. crassipes , inhibiting M. aeruginosa growth, affecting photosystem II, and inducing oxidative stress.