Potential control of toxic cyanobacteria blooms with Moroccan seaweed extracts

Marine macroalgae are a promising source of diverse bioactive compounds with applications in the biocontrol of harmful cyanobacteria blooms (cyanoHABs). In this work, we evaluated the potential algicidal activities of 14 species of seaweed collected from the coast of Souiria Laqdima, Morocco. Methanol extracts were screened in solid and liquid medium against the growth of the toxic cyanobacteria Microcystis aeruginosa and the microalgae Chlorella sp. used as food supplement. The results in solid medium revealed that the algicidal activity was limited to M. aeruginosa with the extract of Bornetia secundiflora showing the highest growth inhibition activity against Microcystis (27.33 ± 0.33 mm), whereas the extracts of Laminaria digitata, Halopytis incurvus, Ulva lactuca, and Sargasum muticum showed no inhibition. In liquid medium, the results indicated that all methanolic extracts of different macroalgae tested have a significant inhibitory effect on M. aeruginosa compared with that of the negative control. The maximum inhibition rates of M. aeruginosa were produced by the extracts of Bifurcaria tuberculata, Codium elongatum, and B. secundiflora. Moreover, the extracts of B. secundiflora recorded the maximum inhibition rate of Chlorella sp. Overall, the results highlight the potential of the extracts from macroalgae to control toxic cyanobacteria species.We acknowledge the projects TOXICROP (823860) funded by the H2020 program MSCA-RISE-2018 and the project VALORMAR (24517) of the 10/SI/2016-I&DT Empresarial- Programas Mobilizadores funded by the European Regional Development Fund (ERDF) and by the European Social Fund (ESF)

Inhibitory effect and mechanism of three macrophytes extract on Microcystis aeruginosa growth and physiology

Macrophytes are a promising source of bioactive compounds with potential applications in the biocontrol of harmful cyanobacteria blooms. In this study, we investigated the inhibitory effects of extracts from three macrophytes (Nasturtium officinale, Potamogeton natans and Ranunculus aquatilis) on Microcystis aeruginosa. We assessed physiological indicators of inhibition on M. aeruginosa, including lipid peroxidation, protein content, superoxide dismutase activity, catalase activity and growth. The chemical composition of the macrophyte extracts and their specific allelochemicals were analysed using high-performance liquid chromatography (HPLC). Results showed that M. aeruginosa growth was significantly inhibited after 8 days of exposure, with inhibitory rate varying from 96.98% to 99.01%. The macrophyte extracts caused cyanobacterial cell membrane and antioxidant defence system damage. Thirteen different compounds were identified as allelochemical compounds that could be responsible for M. aeruginosa growth inhibition and oxidative stress. Our findings suggest that allelopathic compounds from macrophytes may be used to effectively control cyanobacteria blooms and promote the restoration of aquatic ecosystems

Highlighting of the antialgal activity of organic extracts of Moroccan macrophytes: potential use in cyanobacteria blooms control

Many studies have demonstrated the effectiveness of algicidal compounds produced by macrophytes against microalgae. The aim of this study was to assess the algicidal activity of seven Moroccan macrophyte ethyl acetate extracts (MEA) to control harmful algal blooms (HABs). The response and sensitivity of prokaryotic toxic cyanobacteria (Microcystis aeruginosa) and eukaryotic microalgae (Chlorella sp.) were highlighted. The algicidal effect of MEA extracts against the two microalgae was assessed using both the paper disc diffusion and microdilution methods. This last was used in order to evaluate the minimum inhibitory concentrations (MIC) and minimum algicidal concentrations (MAC). Results showed that the growth of both microalgae was significantly inhibited by all MEA extracts. Myriophyllum spicatum organic extract shows the highest growth inhibition activity against M. aeruginosa (35.33 ± 1.53) and Chlorella sp. (30.33 ± 1.15 mm). This stronger inhibitory activity was confirmed by the low MIC (6.25, 12.5 mg/L) and MAC (6.25, 12.5 mg/L) values. Furthermore, results showed different sensitivity between the prokaryotic and eukaryotic microalgae into MEA extracts. Based on the MIC and MAC values, we can distinguish two groups of plants. The first one, including M. spicatum, Ranunculus aquatilis, and Enteromorpha sp., can be considered as a preferable anti-prokaryotic group with a stronger inhibitory activity on M. aeruginosa growth. The second group, constituted by Potamogeton natans, Nasturtium officinale, Elodea sp., and Ceratophyllum sp., has a preferable and stronger inhibitory effect against eukaryotic algae (Chlorella sp.). Overall the results reveal the potential algicidal activity of macrophytes and suggested that MEA extracts could play an important role in biocontrol of HABs