Progress on control of harmful algae by sustained-release technology of allelochemical: A review

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.

Eco-Friendly Algicidal Potential of Zanthoxylum bungeanum Leaf Extracts: Extraction Optimization and Impact on Algal Growth

Zanthoxylum bungeanum leaves were regarded as a waste byproduct for a long period of time, yet their functional components presented potential as novel antimicrobial agents. However, their effectiveness in controlling algal blooms remains unexplored. In this study, the inhibition effect of Z. bungeanum leaf extracts on algal blooms was firstly demonstrated, and the flavonoid profiles of the leaf extract were identified using non-targeted metabolomics analysis. Then, response surface methodology was performed for extraction to further evaluate the feasibility of industrial application. Specifically, the effects of extracts on the cell density, photosynthetic efficiency, and antioxidant activity of Tetrodesmus obliquus was investigated. The results showed that the extraction yield of flavonoids from Z. bungeanum leaves reached 6.85% under the optimized conditions of an ultrasonic power of 600 W, an LSR of 20:1 mL/g, an ethanol concentration of 77.5%, an ultrasonic duration of 18 min, and an ultrasonic temperature of 80 °C, which significantly decreased the Fv/Fm and PIabs values by 54.60% and 98.22%, respectively, after exposure of T. obliquus to 40.0 mg/L Z. bungeanum leaf extract for 66 h. Meanwhile, treatment with Z. bungeanum leaf extract at a dose of 40.0 mg/L generated T-AOC values that were 4.0 times higher than the control without the addition of Z. bungeanum leaf extracts. These results suggest that Z. bungeanum leaf extracts could be used in the development of potentially effective biological algicides. Our study provides data to support the development of algicides and realizes the resource application of Z. bungeanum leaf waste, achieving a synergistic outcome of both economic and ecological benefits.

Optimization of ultrasonic-assisted extraction of total flavonoids from Zanthoxylum bungeanum residue by response surface methodology and evaluation of its algicidal properties

Zanthoxylum bungeanum residue has attracted increasing attention owing to its antibacterial effect, which presents potential as novel antimicrobial agents for the management of algal blooms. In this study, the ability of Z. bungeanum residue extract to control algal blooms has been firstly verified. Then, the response surface methodology was employed to optimize flavonoids yield, the primary antimicrobial component in extract, and the underlying photosynthetic inhibition mechanisms of extract on Tetrodesmus obliquus was investigated. Results showed that the highest yield of total flavonoids was increased to 4.08% when the extraction conditions were a liquid-to-solid ratio of 10:1, ethanol concentration of 60%, extraction temperature of 80°C, and extraction time of 30 min. Meanwhile, treatment with Z. bungeanum residue extract at doses of 40.0 mg/L significantly decreased the Fv/Fm and PIabs values of T. obliquus by 24.36 and 88.87% at 50 h, respectively. The added extract induced damage at multiple levels of physiological and biochemical processes in algal cells, including reduced electron transport capability, disrupted energy transfer in photosystem II, disruption of OEC structure, and altered energy distribution in PSII reaction center. To our knowledge, this study was the first verification of Z. bungeanum residue's algicidal potential, and these findings in our study contribute to a deeper understanding of the allelopathic mechanisms of Z. bungeanum residue extract and offer valuable insights for the management of algal blooms.

Chlorella-Based Biohybrid Microrobot for Removing Both Nutrient and Microalgae toward Efficient Water Eutrophication Treatment

Excessive nutrients and explosive growth of harmful microalgae in water environments are key challenges in the treatment of eutrophication. The development of a low-cost, time-saving, and small-space-suitable research method that can simultaneously remove nutrients and microalgae is highly anticipated. This work first proposed applying microrobots to eutrophication treatment. Phosphate and Microcystisaeruginosa (M. aeruginosa) were selected as representative nutrients and harmful microalgae, respectively, to investigate the efficient removal effect of the microrobots on the two. The Chlorella@Fe3O4@ZIF-8 biohybrid microrobot can not only perform the dual removal of phosphates and M. aeruginosa but also take advantage of its small size and controllable motion to achieve targeted treatment of eutrophication of water in microenvironments such as microchannels, thereby achieving the effect of fundamentally treating the eutrophication. The Chlorella@Fe3O4@ZIF-8 microrobot reveals a new strategy for the treatment of eutrophication and also exploits a new perspective for application research of microrobots.

Effects of artemisinin sustained-release algaecides on in-situ cyanobacterial inhibition and microbes-floating plants dominated ecosystem functions in artificial landscape lake

The artemisinin sustained-release algaecides (ASAs) have been proven to be a safe and effective mean of inhibiting cyanobacteria in laboratory experiments. However, their effectiveness and impacts on ecosystem functions (EF) in natural waters are still unclear. In this study, the in-situ inhibitory effect of ASAs on cyanobacteria in natural waters was investigated over a period of 110 days to assess EF impacts dominated by microbes and floating plants. The results indicated that ASAs had a long-term inhibitory effect on cyanobacteria. ASAs did not affect sediment but increased TOC and TP in the water column in 2-10 days. Microbial diversity and network analyses indicated that ASAs enhanced bacterial diversity, network complexity, and hub-bacteria in networks. Metabolic pathway predictions and CCA analysis showed that ASAs maintained the stability of EF by enhancing the metabolic capacities of bacteria, and the relationships between metabolic microorganisms and environmental factors. PLS-PM revealed that ASAs primarily drove bacterial resistance to cyanobacteria, which was the key mechanism for its long-term inhibition of cyanobacteria. However, the early outbreak of floating plants was not conducive to the long-term inhibition of cyanobacteria by ASAs. This study provides new insights into the mechanisms and ecological impacts of cyanobacterial inhibition by ASAs in complex aquatic environments.

Prolonged Microcystis restraint through allelochemicals sustained-release microspheres regulated by carbon material (CM-AC@SM): Optimal formulation, characterization, effects and synergistic inhibition mechanisms

The Microcystis blooms have caused serious damage to aquatic ecosystems. Microspheres containing allelochemicals with sustained-release properties have the potential to function as a cost-effective and environmentally friendly algaecide against M. aeruginosa. In the current investigation, we successfully optimized the synthesis of allelochemicals sustained-release microspheres regulated by carbon material (CM-AC@SM), which demonstrated a high embedding rate (90.17 %) and loading rate (0.65 %), with an accumulative release rate of 53.27 % on day 30. To investigate the sustained-release mechanism of CM-AC@SM, the sustained-release process of allelochemicals was determined using the Folin-Phenol method and the immersion behavior of the CM-AC@SM was characterized through SEM and XPS. Results showed that allelochemicals were released in the delayed-dissolution mode. In addition, to elucidate the synergistic mechanism of CM-AC@SM towards the inhibition of M. aeruginosa, this study comprehensively assessed the effects of allelochemicals, carbon material and CM-AC@SM on the morphology, antioxidant system activity and photosynthetic activity of M. aeruginosa. The findings indicated that allelochemicals and carbon material induced intracellular protein and nucleic acid leakage by increasing cell membrane permeability, disrupted the extracellular and intracellular morphology of algae, triggered peroxidative damage and restrained antioxidant system activity by stimulating the generation of reactive oxygen species. Simultaneously, the activity of photosystem II was inhibited by allelochemicals and carbon material, substantiated by the reduction in Fv/Fo and Fv/Fm ratios. Hence, CM-AC@SM shows promise in inhibiting M. aeruginosa, offering an efficient approach for the future large-scale control of harmful algal blooms (HABs).

Anticyanobacterial effect of p-coumaric acid on Limnothrix sp. determined by proteomic and metabolomic analysis

Regulating photosynthetic machinery is a powerful but challenging strategy for selectively inhibiting bloom-forming cyanobacteria, in which photosynthesis mainly occurs in thylakoids. P-coumaric acid (p-CA) has several biological properties, including free radical scavenging and antibacterial effects, and studies have shown that it can damage bacterial cell membranes, reduce chlorophyll a in cyanobacteria, and effectively inhibit algal growth at concentrations exceeding 0.127 g/L. Allelochemicals typically inhibit cyanobacteria by inhibiting photosynthesis; however, research on inhibiting harmful algae using phenolic acids has focused mainly on their inhibitory and toxic effects and metabolite levels, and the molecular mechanism by which p-CA inhibits photosynthesis remains unclear. Thus, we examined the effect of p-CA on the photosynthesis of Limnothrix sp. in detail. We found that p-CA inhibits algal growth and damages photosynthesis-related proteins in Limnothrix sp., reduces carotenoid and allophycocyanin levels, and diminishes the actual quantum yield of Photosystem II (PSII). Moreover, p-CA significantly altered algal cell membrane protein systems, and PSII loss resulting from p-CA exposure promoted reactive oxygen species production. It significantly altered algae cell membrane protein systems. Finally, p-CA was found to be environmentally nontoxic; 80 % of 48-h-old Daphnia magna larvae survived when exposed to 0.15 g/L p-CA. These findings provide insight into the mechanism of cyanobacterial inhibition by p-CA, providing a more practical approach to controlling harmful algal blooms.