Étude des blooms toxiques à cyanobactéries dans trois lacs réservoirs du Maroc : résultats préliminaires

Dans le cadre du programme de recherche sur les blooms toxiques à cyanobactéries dans certains lacs de barrage du Maroc, une étude de ce phénomène a été entreprise sur trois retenues : Lalla Takerkoust, Oued Mellah et Al Massira. L'étude taxonomique montre que dans les lacs Lalla Takerkoust et Al Massirra, l'espèce responsable des blooms est Microcystis aeruginosa alors que dans la retenue saumâtre et hypereutrophe Oued Mellah, c'est Microcystis ichthyoblabe.En complément, une étude toxicologique et toxinologique a permis d'évaluer les risques sanitaires potentiels qui peuvent être engendrés par ces blooms. L'hépatotoxicité, pour l'ensemble des blooms récoltés en 1999, a été confirmée par le biotest " souris ". L'application de ce test a montré que le bloom de LallaTakerkoust est hautement toxique (DL50 500 mg/kg) et celui d'Al Massira est intermédiaire (DL50 comprise entre 100 et 500 mg/kg). Les teneurs en microcystines (hépatotoxines) déterminées par ELISA révèlent des concentrations beaucoup plus importantes pour le bloom de Lalla Takerkoust. L'utilisation de la chromatographie liquide haute performance avec détecteur à barrette photodiode, (CLHP-DBP) a permis la détection et l'identification de 2, 4 et 11 variantes de microcystines, respectivement à partir d'extraits du bloom naturel d'Al Massira, Lalla Takerkoust et Oued Mellah. Cependant, la Microcystine-LR n'a été détectée que dans les extraits d'Al Massira et de Takerkoust. L'apparition des blooms toxiques à cyanobactéries dans ces plans d'eau impose dorénavant la prise en considération des nuisances écologiques et des risques sanitaires liés à la présence des microcystines dans ces eaux.During the first part of the toxic cyanobacteria survey program carried out since 1994, Microcystis blooms which periodically occurred in Al Massira, Lalla Takerkoust and Oued Mellah reservoirs were studied. These reservoirs were located at a different hydrographic basin and have a various trophic status. The water was used for irrigation, recreational purpose and/or drinking water supply. The bloom-forming species was identified as Microcystis aeruginosa in Al Massira and Takerkoust freshwater reservoirs whereas in brackish water Oued Mellah reservoir, the bloom-forming species is Microcystis ichthyoblabe.In complement to this ecological studies and in order to assess the potential health risk, a toxicology and toxinology of these Microcystis blooms were undertaken. The hepatotoxicity of lyophilized bloom material collected during bloom periods in 1999 was confirmed by (i. p) mice bioassay. The toxicity assessment revealed that Microcystis Takerkoust bloom was highly toxic with LD50 < 100 mg/kg whereas those from Al Massira and Oued Mellah were respectively characterized by a medium and a low toxicities.The content of microcystins (MCYST) determined by the Enzyme-linked Immunosorbent assay (ELISA) show that MCYST content ranged between 0.37 to 496 µg/g dry weight. It appears that Takerkoust bloom contain 600 to 1300 fold more MCYST than Oued Mellah and Al Massira blooms. The isolation and identification of microcystins variants from bloom extracts were performed using the high performance liquid chromatography with photodiode array detection (HPLC-PDA). This technique provided the separation and identification of at least two microcytins variants from each bloom material. The most number of 11 microcystins were detected from Microcystis ichthyoblabe bloom of Oued Mellah. However, only two and four variants of microcystins were respectively detected from Al Massira and Takerkoust blooms. Among these variants of microcystins solely Microcystin-LR was identified according to the Mcyst-LR authentic sample from extract of Al Massira and Takerkoust blooms.The occurrence of toxic cyanobacteria bloom in these drinking and/or recreational water reservoirs lead us to take into consideration the real health hazard which will be induced by these harmful cyanobacterial blooms

Premier rapport sur la prolifération de marées jaunes ichthyotoxiques à Prymnesium parvum Carter (Haptophyceae) dans le lac hypereutrophe Oued Mellah (Maroc)

Les algues Prymnesiophyceae ou Haptophyceae (Chrysophyta) renferment des espèces capables de pullulations spectaculaires nommées " marées jaunes ". Parmi les Haptophycées, les plus communes sont : Prymnesium parvum, Prymnesium patelliferum et Chrysochromulina polylepis. Ces microalgues ont été souvent incriminées dans des cas de mortalité aiguë de poissons et d'invertébrés aquatiques. P. parvum est connue depuis cent ans comme responsable de blooms toxiques ayant entraîné des mortalités catastrophiques de poissons dans diverses régions du monde.Au Maroc, ces blooms à Prymnesiophyceae n'ont, jusqu'à présent, jamais été signalés. Nos recherches sur les successions phytoplanctoniques du lac hypereutrophe et saumâtre de Oued Mellah (33°30'N-07°20'W), ont mis en évidence la prolifération périodique en automne de l'Haptophycée P. parvum occasionnant des blooms spectaculaires. Les densités cellulaires de P. parvum, espèce dominante, atteignent des maxima de 148·106 cellules·L-1 en 1998 et 169·106 cellules·L-1 en 1999, représentant 34 à 80 % de la biomasse totale. Ces " marées jaunes " coïncident régulièrement avec des mortalités catastrophiques de poissons et d'invertébrés aquatiques dans le lac laissant présager une toxicité aiguë de cette souche de microalgue.Dans ce travail sont présentés les premiers résultats concernant la dynamique interannuelle des blooms à P. parvum et l'influence des conditions physicochimiques particulières des eaux du lac sur leur développement est discutée.The Prymnesiophyceae or Haptophyceae (Chrysophyta) contain species-forming spectacular blooms named yellow tides. Among Haptophyceae, Prymnesium parvum, Prymnesium patelliferum and Chrysochromulina polylepis are the most common. These microalgae were often involved in acute fish and aquatic invertebrates mortality cases. P. parvum, known since hundred years as being responsible for toxic blooms, has induced catastrophic fish mortality in various areas throughout the world.In Morocco, blooms of Prymnesiophyceae have never been reported up till now. Studies on phytoplankton successions in the hypertrophic brackish Oued Mellah lake (33°30'N-07°20'W) show a periodic autumnal proliferation of P. parvum. This species, which cellular densities reach a maxima of 148·106 cells·L-1 in 1998 and 169·106 cells·L-1 in 1999, dominates the other phytoplanctonic species with 34 to 80% of the total biomass. The yellow tides coincide regularly with dramatic fish and aquatic invertebrates mortality in the lake leading to the prediction of an acute toxicity due to this microalgae.The principal aim of this study was to present the first results concerning the interannual dynamics of P. parvum blooms and to discuss the influence of the particular physical and chemical water characteristics on their development

Role of rhizospheric microbiota as a bioremediation tool for the protection of soil-plant systems from microcystins phytotoxicity and mitigating toxin-related health risk

Frequent toxic cyanoblooms in eutrophic freshwaters produce various cyanotoxins such as the monocyclic heptapeptides microcystins (MCs), known as deleterious compounds to plant growth and human health. Recently, MCs are a recurrent worldwide sanitary problem in irrigation waters and farmland soils due to their transfer and accumulation in the edible tissues of vegetable produce. In such cases, studies about the persistence and removal of MCs in soil are scarce and not fully investigated. In this study, we carried out a greenhouse trial on two crop species: faba bean (Vicia faba var. Alfia 321) and common wheat (Triticum aestivum var. Achtar) that were grown in sterile (microorganism-free soil) and non-sterile (microorganism-rich soil) soils and subjected to MC-induced stress at 100 µg equivalent MC-LR L−1. The experimentation aimed to assess the prominent role of native rhizospheric microbiota in mitigating the phytotoxic impact of MCs on plant growth and reducing their accumulation in both soils and plant tissues. Moreover, we attempted to evaluate the health risk related to the consumption of MC-polluted plants for humans and cattle by determining the estimated daily intake (EDI) and health risk quotient (RQ) of MCs in these plants. Biodegradation was liable to be the main removal pathway of the toxin in the soil; and therefore, bulk soil (unplanted soil), as well as rhizospheric soil (planted soil), were used in this experiment to evaluate the accumulation of MCs in the presence and absence of microorganisms (sterile and non-sterile soils). The data obtained in this study showed that MCs had no significant effects on growth indicators of faba bean and common wheat plants in non-sterile soil as compared to the control group. In contrast, plants grown in sterile soil showed a significant decrease in growth parameters as compared to the control. These results suggest that MCs were highly bioavailable to the plants, resulting in severe growth impairments in the absence of native rhizospheric microbiota. Likewise, MCs were more accumulated in sterile soil and more bioconcentrated in root and shoot tissues of plants grown within when compared to non-sterile soil. Thereby, the EDI of MCs in plants grown in sterile soil was more beyond the tolerable daily intake recommended for both humans and cattle. The risk level was more pronounced in plants from the sterile soil than those from the non-sterile one. These findings suggest that microbial activity, eventually MC-biodegradation, is a crucial bioremediation tool to remove and prevent MCs from entering the agricultural food chain. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.This project has received funding from the European Union?s Horizon 2020 research and innovation program under the Marie Sk?odowska-Curie grant agreement No. 823860 and co-sup-ported by the strategical funding from FCT UIDB/04423/2020 and UIDP/04423/2020

Evidence for a Novel Marine Harmful Algal Bloom: Cyanotoxin (Microcystin) Transfer from Land to Sea Otters

“Super-blooms” of cyanobacteria that produce potent and environmentally persistent biotoxins (microcystins) are an emerging global health issue in freshwater habitats. Monitoring of the marine environment for secondary impacts has been minimal, although microcystin-contaminated freshwater is known to be entering marine ecosystems. Here we confirm deaths of marine mammals from microcystin intoxication and provide evidence implicating land-sea flow with trophic transfer through marine invertebrates as the most likely route of exposure. This hypothesis was evaluated through environmental detection of potential freshwater and marine microcystin sources, sea otter necropsy with biochemical analysis of tissues and evaluation of bioaccumulation of freshwater microcystins by marine invertebrates. Ocean discharge of freshwater microcystins was confirmed for three nutrient-impaired rivers flowing into the Monterey Bay National Marine Sanctuary, and microcystin concentrations up to 2,900 ppm (2.9 million ppb) were detected in a freshwater lake and downstream tributaries to within 1 km of the ocean. Deaths of 21 southern sea otters, a federally listed threatened species, were linked to microcystin intoxication. Finally, farmed and free-living marine clams, mussels and oysters of species that are often consumed by sea otters and humans exhibited significant biomagnification (to 107 times ambient water levels) and slow depuration of freshwater cyanotoxins, suggesting a potentially serious environmental and public health threat that extends from the lowest trophic levels of nutrient-impaired freshwater habitat to apex marine predators. Microcystin-poisoned sea otters were commonly recovered near river mouths and harbors and contaminated marine bivalves were implicated as the most likely source of this potent hepatotoxin for wild otters. This is the first report of deaths of marine mammals due to cyanotoxins and confirms the existence of a novel class of marine “harmful algal bloom” in the Pacific coastal environment; that of hepatotoxic shellfish poisoning (HSP), suggesting that animals and humans are at risk from microcystin poisoning when consuming shellfish harvested at the land-sea interface

Capacité de stockage intracellulaire de l'azote et du phosphore chez

Le comportement nutritionnel de Microcystis aeruginosa et de Synechocystis sp. en période de carence des nutriments a été évalué par des expériences simultanées de carence et d'enrichissements en azote et en phosphore. Ces manipulations ont permis d'estimer les réserves intracellulaires en nutriments stockées par ces deux espèces de cyanobactéries et de voir dans quelle mesure ces réserves soutiennent leur croissance au cours de la carence. L'évaluation de la capacité de stockage des nutriments a été faite en culture sur milieu naturel (eau du lac pour Microcystis et eau usée pour Synechocystis) et sur milieu enrichi BG 13. La croissance des deux souches d'algues est beaucoup plus rapidement affectée par la carence en azote (N-NO-3). Le nombre de cellules filles, produites à partir des réserves intracellulaires en azote, est pratiquement similaire pour les deux types de milieux de culture utilisés. A l'inverse, malgré la carence en phosphore, les deux cyanobactéries poursuivent leur croissance en phase exponentielle beaucoup plus longtemps grâce aux réserves qui ne sont épuisées qu'au 8ème jour de mise en carence. Le nombre de cellules filles produites à partir des réserves intracellulaires en phosphore, est légèrement plus faible en culture sur milieu BG 13 que sur milieu naturel. Les deux souches stockent des quantités en azote et en phosphore non négligeables qui leur permettent de maintenir leur croissance lorsque les nutriments font défaut dans le milieu

La tectonique panafricaine du secteur d&#226;&#128;&#153;Igherm : implication des d&#244;mes extensifs tardi a post-orogeniques (Anti-Atlas Occidental, Maroc)

L&rsquo;&eacute;volution tectonique tardi-orog&eacute;nique panafricaine du secteur d&rsquo;Igherm (Anti-Atlas occidental, Maroc) se caract&eacute;rise par l&rsquo;exhumation des parties profondes pal&eacute;oprot&eacute;rozo&iuml;ques &agrave; l&rsquo;image des d&ocirc;mes extensifs. Elle est contr&ocirc;l&eacute;e par un d&eacute;tachement principal ductile de faible pendage et des d&eacute;tachements de fort pendage de type extensionnel qui succ&egrave;dent &agrave; un raccourcissement r&eacute;gional de direction NW-SE. Le d&eacute;tachement principal subhorizontal, est soulign&eacute; par des mylonites de faible degr&eacute; m&eacute;tamorphique. Il s&eacute;pare deux unit&eacute;s : l&rsquo;unit&eacute; inf&eacute;rieure (complexe m&eacute;tamorphique du Pal&eacute;oprot&eacute;rozo&iuml;que) &agrave; comportement ductile et l&rsquo;unit&eacute; sup&eacute;rieure (Quartzites n&eacute;oprot&eacute;rozo&iuml;ques du Supergroupe de l&rsquo;Anti-Atlas) &agrave; comportement fragile. Cette &eacute;volution co&iuml;ncide avec la mise en place des bassins &laquo; suprad&eacute;tachement &raquo; du Supergroupe de Ouarzazate durant l&rsquo;extension qui aurait d&eacute;but&eacute; apr&egrave;s le raccourcissement panafricain dat&eacute;s vers 650 Ma. L&rsquo;&eacute;v&egrave;nement extensionnel peut &ecirc;tre g&eacute;n&eacute;ralis&eacute; &agrave; tout l&rsquo;Anti-Atlas occidental.<br><br>La evoluci&oacute;n tect&oacute;nica tardi-orog&eacute;nica panafricana del sector de Igherm (Anti-Atlas occidental, Marruecos) se caracteriza por la exhumaci&oacute;n de las partes profundas proterozoicas como domos extensivos. Est&aacute; controlada por un despegue principal d&uacute;ctil con poco buzamiento y despegues con alto buzamiento de tipo extensional que se sobreponen a un acortamiento regional de direcci&oacute;n NO-SE. El despegue principal subhorizontal viene marcado por milonitas con metamorfismo de grado bajo. Este accidente separa dos unidades : la unidad inferior (complejo metam&oacute;rfico del Paleoproterozoico) de comportamiento d&uacute;ctil y la unidad superior (cuarcitas del neoproterozoico del Supergrupo del Anti-Atlas) de comportamiento fr&aacute;gil. Esta evoluci&oacute;n coincide con el origen de las cuencas de &laquo;supra-detachment&raquo; del Supergrupo de Ouarzazate durante la extensi&oacute;n que se habr&iacute;a producido despu&eacute;s del acortamiento panafricano (hacia 650 Ma). Este evento extensional est&aacute; generalizado en todo el Anti-Atlas occidental

Taxonomy and geographic distribution of potential toxic cyanobacterial strains in Morocco

In Morocco, poisoning events of fish, aquatic birds and livestock have been observed in some reservoirs and shallow lakes. In all cases, the reasons for animal mortality reasons have not been confirmed and the toxic cyanobacteria strains that were abundant in these water bodies have been suggested as their cause. Since 1994, the authors started taxonomic, ecological and toxicological studies by collecting samples from various lakes reservoirs and ponds. The results show that more than 18 out of 26 lakes reservoirs used for human water supply contained at least one species of planktonic cyanobacteria, where the genus Microcystis was dominant (Microcystis aeruginosa f. aeruginosa, M. aeruginosa f. flos-aquae, M. ichthyoblabe, M. pulverea f. delicatissima) and was associated with Oscillatoria, Planktothrix, Anabaena, Aphanizomenon, Phormidium and other genera. Taxonomic studies shows that among more than 150 cyanobacteria taxa identified in Moroccan freshwater ecosystems, 35 are potentially toxic. For several species, the toxicity of both natural blooms and isolated strains lyophilized material was confirmed by mouse bioassay and the microcystins content evaluated by the Enzyme-linked immunosorbent assay (ELISA). A map of geographic distribution of Microcystis strains inventoried in moroccan water bodies is presented