Remediation Strategies to Control Toxic Cyanobacterial Blooms: Effects of Macrophyte Aqueous Extracts on Microcystis aeruginosa (Growth, Toxin Production and Oxidative Stress Response) and on Bacterial Ectoenzymatic Activities

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.

Potential Use of Aquatic Vascular Plants to Control Cyanobacterial Blooms: A Review

“…The stability of allelochemical compounds in water depends on temperature and other factors such as light intensity, pH level and dissolved oxygen content [59,103,144,145]. Nakai et al [103] showed that increasing temperature (from 20 to 30 • C) and light intensity (from 25 to 75 µmol m −2 s −1 ) reduce inhibition of Microcystis aeruginosa growth, and that this process is mediated by the impact of polyphenols ((+) catechin, eugeniin, ellagic acid, gallic acid and pyrogallic acid) and fatty acids (nonanoic acid, cis-6-octadecenoic acid and cis-9-octadecenoic acid), which are also produced by Myriophyllum spicatum [6]. Other researchers report the effect of light intensity on the stability of allelopathically active phenolic compounds in water [144,146].…”

“…The increase in frequency and duration of blue-green algal (cyanobacterial) blooms poses serious threats to the environment, including degradation of local and global water resources [1][2][3][4][5][6]. This is due to the production of a wide range of toxic secondary metabolites, namely cyanotoxins, by some species of planktonic microalgae (Microcystis aeruginosa (Kützing) Kützing; Dolichospermum flosaquae (Bornet & Flahault) P.Wacklin, L.Hoffmann & Komárek (=Anabaena flosaquae Brébisson ex Bornet and Flauhault); Aphanizomenon flosaquae Ralfs ex Bornet and Flahault; Planktothrix agardhii (Gomont) Anagnostidis and Komárek; Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis and Komárek; Cylindrospermopsis raciborskii (Woloszynska) Seenaya and Sabbaraju (=Raphidiopsis raciborskii (Woloszynska) Aguilera, Berrendero Gómez, Kastovsky, Echenique and Salerno), etc.)…”

Nature‐based coagulants for drinking water treatment: An ecotoxicological overview

“…The cyanobacterial culture was constituted of M. aeruginosa (NCBI accession number: PRJDB11480) sampled during bloom occurrence from the eutrophic reservoir of Lalla Takerkoust, Marrakech (31 36 0 N, 8 20 0 W), isolated and maintained since October 2015 at a room culture in batch system on Z8 medium (63 μmol photons/m 2 /s with a light/dark of 15/9 h at 26 ± 2 C) and molecularly identified by 16S rRNA sequencing (Tazart et al, 2021).…”

Inhibitory Effect of Aqueous Extracts from Egeria densa Planch. on Cyanobacteria Microcystis aeruginosa (Kützing) Lemmermann Growth

“…These fishes directly feed on cyanobacteria, including toxin-producing Microcystis aeruginosa [10]. Moreover, the utilization of macrophytes and their extracts as a biological control method for cyanobacteria has been widely adopted in previous studies due to their minimal impact on the ecosystem and human health [11,12]. A new generation of natural algaecides based on allelochemicals from aquatic plants increased the attention of researchers because of their low toxicity on other aquatic life [13].…”