Abstract
Increasing toxic cyanobacterial blooms in freshwater demand environmentally friendly solutions to control their growth and toxicity, especially in arid countries, where most drinking water is produced from surface reservoirs. We tested the effects of macrophyte allelochemicals on Microcystis aeruginosa and on the fundamental role of bacteria in nutrient recycling. The effects of Ranunculus aquatilis aqueous extract, the most bioactive of four Moroccan macrophyte extracts, were tested in batch systems on M. aeruginosa growth, toxin production and oxidative stress response and on the ectoenzymatic activity associated with the bacterial community. M. aeruginosa density was reduced by 82.18%, and a significant increase in oxidative stress markers was evidenced in cyanobacterial cells. Microcystin concentration significantly decreased, and they were detected only intracellularly, an important aspect in managing toxic blooms. R. aquatilis extract had no negative effects on associated bacteria. These results confirm a promising use of macrophyte extracts, but they cannot be generalized. The use of the extract on other toxic strains, such as Planktothrix rubescens, Raphidiopsis raciborskii and Chrysosporum ovalisporum, caused a reduction in growth rate but not in cyanotoxin content, increasing toxicity. The need to assess species-specific cyanobacteria responses to verify the efficacy and safety of the extracts for human health and the environment is highlighted.
Highlights
This paper considers for the first time the harmful cyanobacterial bloom control by allelochemicals from several points of view, including toxin production and associated bacterial communities, providing a more complete picture of the possible remediation activities, not limited to growth inhibition
Comparison of Anticyanobacterial Activity Shown by Different Macrophyte Aqueous Extracts
The results show that all tested macrophytes inhibited M. aeruginosa growth
Summary
Cyanobacterial blooms can produce a variety of compounds (e.g., cyanotoxins and taste and odor chemicals) that may have a negative impact on water quality and can represent a risk for human and animal health through drinking, recreational activities, consumption of contaminated food and feed items and irrigation [2,3,4]. The control and prevention of cyanobacterial blooms and their toxicity, in terms of toxins production, is an important goal for monitoring water quality, drinking water supplies and prevention of adverse environmental and health impacts. Document for Development of WHO Guidelines for Drinking-Water Quality and Guidelines for Safe Recreational Water Environments; World Health. Isolation and Identification of Algicidal Compound from Streptomyces and Algicidal Mechanism to Microcystis aeruginosa.
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