Identification of algicidal monoterpenoids from four chemotypes of Cinnamomum camphora and their algicidal mechanisms on Microcystis aeruginosa

Long-term suppression of Microcystis aeruginosa by tannic acid: Risks of microcystin pollution and proteomic mechanisms

Harmful algal blooms are a critical eco-environmental issue with severe impacts on aquatic ecosystems and human health. Tannic acid (TA) has been suggested as an effective algal bloom control, but the molecular mechanisms of its interaction with algae cells and its effects on algal toxin release remain unclear. This study tracked toxin production and release in the toxigenic species Microcystis aeruginosa (M. aeruginosa) exposed to TA, revealing underlying mechanisms through proteomic analysis. High TA doses effectively inhibited M. aeruginosa growth and microcystin-leucine-arginine (MC-LR) production. However, at a specific TA concentration, M. aeruginosa produced and released more MCs, with extracellular MC-LR levels peaking at 1.91 times the control on day 15. Proteomic analysis indicated upregulation of proteins related to the tricarboxylic acid (TCA) cycle, glycolysis, and leucine and arginine biosynthesis, suggesting a compensatory response in M. aeruginosa under TA stress that enhanced cellular energy supply and MC-LR biosynthesis. In addition, TA exposure significantly downregulated proteins involved in ion and metal-cluster binding, disrupting electron transfer and photosynthesis. This study provides new insights into TA-induced MC-pollution risks and TA's mechanisms in algae suppression, offering guidance for its application in algal bloom control.

Biological and Chemical Approaches for Controlling Harmful Microcystis Blooms

The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O2, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H2O2 are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies.