Cyanobacterial toxins: A short review on phytotoxic effect in an aquatic environment

Cyanobacteria are photosynthetic prokaryotes which frequently form blooms in eutrophic water bodies. Some species of cyanobacteria are able to produce toxins (cyanotoxins) that can cause aquatic environment and diverse organisms living there to be at a serious risk. One of the more serious impacts of eutrophication on aquatic ecosystems is the disappearance of submerged macrophytes and the shift to a phytoplankton-dominated state. Hence, cyanobacterial blooms may be of significant negative ecological impact. This may represent a sanitary risk due to toxin bioaccumulation and biotransfer through the food chain. So, with the increasing number of new researches made on this subject, we propose this paper to review clearly many recent and original reports that have demonstrated the effects of cyanotoxins on some biological and physiological pathways in different aquatic plants.Keywords: Cyanotoxins, microcystins, aquatic plants, eco-physiological, sanitary risk

CyanoHAB Occurrence and Water Irrigation Cyanotoxin Contamination: Ecological Impacts and Potential Health Risks

The world-wide occurrence of harmful cyanobacteria blooms “CyanoHAB” in fresh and brackish waters creates problems for all life forms. During CyanoHAB events, toxic cyanobacteria produce cyanotoxins at high levels that can cause chronic and sub-chronic toxicities to animals, plants and humans. Cyanotoxicity in eukaryotes has been mainly focused on animals, but during these last years, data, related to cyanotoxin (mainly microcystins, MCs) impact on both aquatic and terrestrials crop plants irrigated by water containing these toxins, have become more and more available. This last cited fact is gaining importance since plants could in a direct or indirect manner contribute to cyanotoxin transfer through the food chain, and thus constitute a potent health risk source. The use of this contaminated irrigation water can also have an economical impact which appears by a reduction of the germination rate of seeds, and alteration of the quality and the productivity of crop plants. The main objective of this work was to discuss the eventual phytotoxicity of cyanotoxins (microcystins) as the major agricultural impacts induced by the use of contaminated water for plant irrigation. These investigations confirm the harmful effects (ecological, eco-physiological, socio-economical and sanitary risk) of dissolved MCs on agricultural plants. Thus, cyanotoxin phytotoxicity strongly suggests a need for the surveillance of CyanoHAB and the monitoring of water irrigation quality as well as for drinking water

Compensatory Growth Induced in Zebrafish Larvae after Pre-Exposure to a Microcystis aeruginosa Natural Bloom Extract Containing Microcystins

Early life stage tests with zebrafish (Danio rerio) were used to detect toxic effects of compounds from a Microcystis aeruginosa natural bloom extract on their embryolarval development. We carried out the exposure of developing stages of fish to complex cyanobacterial blooms containing hepatotoxic molecules - microcystins. Fish embryo tests performed with the bloom extract containing 3 mg·L−1 Eq microcystin-LR showed that after 24 h of exposure all fish embryos died. The same tests performed with other diluted extracts (containing 0.3, 0.1 and 0.03 mg·L−1 Eq microcystin-LR) were shown to have an influence on zebrafish development and a large number of embryos showed malformation signs (edema, bent and curving tail). After hatching the larvae were transferred to a medium without toxins to follow the larval development under the new conditions. The specific growth of the pre-exposed larvae was significantly more important than that of the control larvae. This may represent a compensatory growth used to reduce the difference in size with the control fish noted after hatching

Cylindrospermopsin: A Decade of Progress on Bioaccumulation Research

Cylindrospermopsin (CYN) is rapidly being recognised as one of the most globally important of the freshwater algal toxins. The ever-expanding distribution of CYN producers into temperate zones is heightening concern that this toxin will represent serious human, as well as environmental, health risks across many countries. Since 1999, a number of studies have demonstrated the ability for CYN to bioaccumulate in freshwater organisms. This paper synthesizes the most current information on CYN accumulation, including notes on the global distribution of CYN producers, and a précis of CYN’s ecological and human effects. Studies on the bioaccumulation of CYN are systematically reviewed, together with an analysis of patterns of accumulation. A discussion on the factors influencing bioaccumulation rates and potential is also provided, along with notes on detection, monitoring and risk assessments. Finally, key gaps in the existing research are identified for future study

Diversity of cyanobacteria and cyanotoxins in Hartbeespoort Dam, South Africa

The South African Hartbeespoort Dam is known for the occurrence of heavy Microcystis blooms. Although a few other cyanobacterial genera have been described, no detailed study on those cyanobacteria and their potential toxin production has been conducted. The diversity of cyanobacterial species and toxins is most probably underestimated. To ascertain the cyanobacterial composition and presence of cyanobacterial toxins in Hartbeespoort Dam, water samples were collected in April 2011. In a polyphasic approach, 27 isolated cyanobacterial strains were classified morphologically and phylogenetically and tested for microcystins (MCs), cylindrospermopsin (CYN), saxitoxins (STXs) and anatoxin-a (ATX) by liquid chromatography–tandem mass spectrometry (LC–MS/MS) and screened for toxin-encoding gene fragments. The isolated strains were identified as Sphaerospermopsis reniformis, Sphaerospermopsis aphanizomenoides, Cylindrospermopsis curvispora, Raphidiopsis curvata, Raphidiopsis mediterrranea and Microcystis aeruginosa. Only one of the Microcystis strains (AB2011/53) produced microcystins (35 variants). Forty-one microcystin variants were detected in the environmental sample from Hartbeespoort Dam, suggesting the existence of other microcystin producing strains in Hartbeespoort Dam. All investigated strains tested negative for CYN, STXs and ATX and their encoding genes. The mcyE gene of the microcystin gene cluster was found in the microcystin-producing Microcystis strain AB2011/53 and in eight non-microcystin-producing Microcystis strains, indicating that mcyE is not a good surrogate for microcystin production in environmental samples.Grant 196085/V10 (Monitoring of Cyanotoxins in Southern Africa) from The Research Council of Norway.http://www.publish.csiro.au/nid/126.htmhb201

Caractérisation biochimique et moléculaire d’efflorescences à cyanobactéries toxiques dans le réservoir Lalla Takerkoust (Maroc)

En complément aux travaux réalisés depuis 1994 sur la toxicologie des cyanobactéries dans différents lacs-réservoirs du Maroc, le présent travail se propose d'apporter des informations supplémentaires en se fixant trois principaux objectifs: 1) Mise à jour de la base de données de la variation temporelle des teneurs en cyanotoxines intracellulaires (microcystines) d'efflorescences cyanobactériennes fréquemment occasionnés dans le lac réservoir Lalla Takerkoust; 2) Évaluation de la contamination des eaux brutes du lac par les microcystines (MC) (quantification des MC extracellulaires); 3) Caractérisation de la diversité moléculaire des souches cyanobactériennes par la détection des gènes de la synthèse des cyanotoxines (MC) en utilisant les deux méthodes multiplex‑PCR et RFLP (Restriction Fragment Length Polymorphism). L'analyse par HPLC des échantillons 2005 et 2006 d'efflorescences cyanobactériennes a montré qu'il y a une variation qualitative et quantitative des microcystines intracellulaires (MC). L'évaluation des teneurs en MC et dissoutes dans l'eau brute, par ELISA, a révélé des quantités très importantes de MC extracellulaires avec un maximum de 95,4 μg•L‑1 durant le mois de décembre 2005 (phase de déclin du développement des cyanobactéries). En général, durant l'année, les concentrations des MC dissoutes restent toujours au‑dessus de la valeur guide recommandée par l'OMS pour l'eau de boisson (1 μg•L‑1). La caractérisation moléculaire, recherche du gène de synthèse des MC, a confirmé que seule Microcystis aeruginosa est la souche productrice des MC au sein de la fraction phytoplanctonique. Ce travail a pour mérite de confirmer pour la première fois au Maroc que, lors de proliférations d'efflorescences cyanobactériennes à Microcystis, les teneurs en MC dans les eaux brutes du lac sont si importantes qu'il est fortement recommandé de prendre en compte les divers risques sanitaires potentiellement engendrés par cette contamination lors de l'utilisation de cette eau (eau d'alimentation sans traitement, eau récréative, eau d'irrigation, etc.). D'après ces résultats, nous concluons que la mise en place d'un programme de surveillance des cyanobactéries et de contrôle des cyanotoxines (MC) doit être basée sur la caractérisation biochimique (détermination de la nature et de la quantité de toxines produites) et complémentée par la caractérisation génétique des souches potentiellement productrices de ces cyanotoxines.Complementary to earlier research carried out since 1994 related to toxic cyanobacteria in different Moroccan lake-reservoirs, this work furnishes new data relating to this research topic. Three major objectives were established: 1) update knowledge concerning the temporal variation of the intracellular contents of cyanotoxines (microcystines, MCs) in cyanobacteria blooms, which frequently occur in the Lalla Takerkoust lake-reservoir; 2) evaluate the MC contamination of raw waters (quantification of extracellular MCs); 3) molecular characterization of cyanobacteria MC producing strains (detection of genes involved in MC synthesis using two methods, multiplex-PCR and RFLP (Restriction fragment length polymorphism)). For bloom samples collected during 2005-2006, the HPLC analysis showed quantitative and qualitative temporal variation in intracellular MCs. Evaluation of the extracellular MC content, determined by ELISA analysis, revealed a maximum concentration of 95.4 μg•L-1 in raw water. This value was measured during December 2005, corresponding to the decline of a Microcystis bloom (cell lysis and MC release into the surrounding water). In general, the dissolved MC concentrations in raw water always remained above the guideline value recommended by the World Health Organization for drinking water (1 μg•L-1). The genetic analysis, based on the detection of the MC synthetase gene ( mcyA gene), confirmed that among the bloom-forming phytoplanktonic fraction, Microcystis aeruginosa is the only MC producing strain. This work thus confirms for the first time in Morocco that during Microcystis blooms, the MC extracellular content greatly exceeds WHO guidelines. It is strongly recommended that the various potential sanitary risks involved in the use of such untreated water (drinking, recreation and irrigation waters) be taken into account. Based on these results, we conclude that the establishment of any successful monitoring programs for cyanobacteria and MC should be based first on biochemical characterization (identification and determination of the amount of produced toxins) and be supplemented by the genetic characterization of the toxin-producing strains