Impact of unidentified secondary metabolites from five new cyanobacterial species on aquatic plant

Cyanobacteria are a great source of bioactive secondary metabolites, exerting harmful (cyanotoxins) or beneficial (drugs) effects on other organisms. In this work, we investigated the impact of the cyanobacteria strains Jaaginema sp. and Trichormus variabilis, and the newly described species Komarekiella chia, Nodularia mediterranea, and Iphianassa zackieohae with unknown metabolome on Lemna trisulca macrophyte. The experiments were prepared in short- (cyanobacteria extracts, up to 24h) and long-term (co-cultivation in BG11, 2 weeks) periods. Co-cultivation with I. zackieohae cells initially stimulated plant growth, but after 14 days the value was close to the control, while the remaining cyanobacteria slightly inhibited the accumulation of macrophyte biomass. After 14 days of co-cultivation, K. chia, and N. mediterranea significantly increased the total amount of protein in the plant [mg·g^-1 dry weight], by 33% and 44%, respectively. The extracts of all analyzed cyanobacteria significantly increased the respiration process after 24-hour exposure. The tested cyanobacteria strains, except I. zackieohae, decreased the content of chlorophylls a and b by an average of 48% and 53%, respectively. Jaaginema sp. extract temporarily inhibited plant photosynthesis just within 7 minutes. The above effects on photosynthesis were confirmed by ultrastructural imaging of chloroplasts. Oxidative stress induced after treatments is also discussed.