Cyanobacterial sensitivity and response to hydrogen peroxide treatment

Oxidative stress caused by reactive oxygen species like hydrogen peroxide (H2O2) is a critical factor in aquatic ecosystems, often triggered by environmental changes such as high light exposure, pollution, or management strategies like chemical treatments to control harmful blooms. Understanding how cyanobacteria respond to such stress is essential for predicting bloom dynamics, assessing the risks associated with toxin production, and developing effective mitigation strategies. To address these questions, growth, photosynthesis efficiency, toxin production (cylindrospermopsin and microcystins), and the expression of toxin-related gene clusters (cyr and mcy) under controlled H2O2 exposure were investigated, providing valuable insights into the ecological resilience and adaptability of these strains. This study investigates the responses of various cyanobacterial species, including Raphidiopsis raciborskii, Microcystis aeruginosa and Aphanizomenon flos-aquae, to oxidative stress induced by hydrogen peroxide (H2O2) exposure over 48 hours. The selected strains, originating from different localities and continents, represent a diverse range of toxin-producing and non-toxin-producing cyanobacteria. The relative growth trends reveal significant strain-specific differences, with 2012/KM1/D3 exhibiting the steepest decline, suggesting a severe impact on its growth. In contrast, KLL07 showed the least growth reduction, maintaining higher OD levels, indicative of greater resilience. PSII activity data further supports these observations, with KLL07 showing a marked increase in PSII efficiency at 24 and 48 hours, whereas strains like CS-506 and 2012/KM1/D3 experienced pronounced declines. These results suggest that KLL07 has a robust adaptive mechanism to maintain photosynthetic efficiency and growth under stress, whereas other strains are more susceptible to damage, possibly due to differences in their genetic or physiological responses. Additional data for the toxic strains R. raciborskii and M. aeruginosa, including toxin gene expression and toxin production, provided further insights into their responses to oxidative stress. Expression of the cyr genes in R. raciborskii during H2O2 exposure showed some fluctuations compared to the control, however, statistical analysis did not reveal any significant differences. In contrast, the results for mcy gene expression in M. aeruginosa revealed a downregulation during H2O2 exposure. Furthermore, exposure to 5 mg/L H2O2 resulted in a significant decrease in the intracellular cyanotoxin content (CYN or MC per mL) for all investigated toxic strains after 48 hours of treatment. These findings highlight that oxidative stress not only affects growth and photosynthesis, but also impacts toxin production and gene expression, with toxic strains showing variable responses in their ability to regulate toxin biosynthesis pathways under stress conditions suggesting potential differences in their adaptive mechanisms and resilience to environmental stressors. This variability could have significant ecological implications, influencing bloom toxicity and treatment in natural ecosystems.

Presentation Preference: Either

Primary Presenter: Nada Tokodi, University of Novi Sad (nada.tokodi@dbe.uns.ac.rs)

Authors:

Nada Tokodi, Department of Biology and Ecology, Faculty of Sciences, University of Novi Sad  (nada.tokodi@dbe.uns.ac.rs)

Klimczak Barbara, Laboratory of Metabolomics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University  (barbara.klimczak@doctoral.uj.edu.pl)

Damjana Drobac Backović, Department of Biology and Ecology, Faculty of Sciences, University of Novi Sad  (damjana.drobac@dbe.uns.ac.rs)

Adam Antosiak, Laboratory of Metabolomics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University  (adam.antosiak@doctoral.uj.edu.pl)

Mikołaj Kokociński, Department of Hydrobiology, Faculty of Biology, Adam Mickiewicz University  (mikolaj.kokocinski@amu.edu.pl)

Anusuya Willis, Australian National Algae Culture Collection, CSIRO  (anusuya.willis@csiro.au)

Dariusz Dziga, Laboratory of Metabolomics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University  (dariusz.dziga@uj.edu.pl)