Physiological response of <scp> <i>Microcystis aeruginosa</i> </scp> exposed to aqueous extracts of <scp> <i>Pistia stratiotes</i> </scp> and <i>Pontederia crassipes</i>

Macrophyte extracts inhibit cyanobacteria growth, offering a sustainable solution for bloom control. The present study aimed to evaluate the response of Microcystis aeruginosa to aqueous extracts obtained from the dried biomass of Pistia stratiotes L. and Pontederia crassipes Mart. Solms. The parameters analyzed were cyanobacterial growth, photosynthesis, generation of reactive oxygen species, and antioxidative response. The chemical profile of the aqueous extracts upon incubation was also analyzed. Both extracts (4.0 g.L^-1) inhibited cyanobacterial growth in 6 days: 100% inhibition for P. stratiotes and 60% inhibition for P. crassipes. Photosynthetic activity was also inhibited: 99% inhibition for P. stratiotes and 12% inhibition 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 the concentration of intracellular reactive oxygen species in cyanobacterial cultures. Superoxide dismutase( SOD) enzymatic activity increased in cultures exposed to P. stratiotes extracts. The transcription of the sod gene was not altered but the transcription of the peroxiredoxin gene (prxA) increased. Upon incubation of the macrophyte extracts with M. aeruginosa cultures, phenol concentrations decreased, and their metabolic profile changed. Thus, P. stratiotes extract outperformed P. crassipes in inhibiting M. aeruginosa growth. P. stratiotes extracts obtained from the plant dry biomass present allelopathic activity on cyanobacteria and can be used as a sustainable alternative to mitigate blooms. PRACTITIONER POINTS: Aqueous extracts from dried biomass of P. stratiotes and P. crassipes inhibited M. aeruginosa growth. P. stratiotes extract suppressed photosystem II activity, while P. crassipes did not. Both extracts elicited reactive oxygen species (ROS) production in cells. Peroxiredoxin gene expression upregulated by extract exposure. P. stratiotes extract increased superoxide dismutase (SOD) activity in cells.