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

Substances bioactives élaborées par des cyanobactéries isolées de certains écosystèmes aquatiques marocains

Durant la saison chaude, plusieurs écosystèmes aquatiques (lacs, étangs, rivières, …) connaissent une croissance importante des cyanobactéries conduisant à la formation des efflorescences (blooms). Les cyanobactéries sont capables de produire une multitude de substances antimicrobiennes : antibactériennes, algicides, antifongique, antivirales et même des substances toxiques. L’objectif de ce travail constitue en l’étude des effets des substances bioactives produites par 10 souches de cyanobactéries isolées de certains écosystèmes aquatiques marocains. Ainsi, nous avons purifié et identifié les souches cyanobactéries isolées et nous avons testé l’activité de leurs substances extracellulaires et intracellulaires sur des micro-organismes d’intérêt sanitaire. Nous avons aussi évalué leur toxicité par le biotest souris. L’identification des 10 souches de cyanobactéries étudiées a montré qu’elles appartiennent à 3 familles à savoir les Oscillatoriaceae, les Nostocaceae et les Chroococcaceae. L’étude des effets des substances intracellulaires produites par ces souches de cyanobactéries, a montré que les extraits aqueux de ces substances ne donnent pas généralement une importante activité. Par contre, ces substances extraites par le méthanol inhibent la croissance de Micrococcus luteus et de Bacillus cereus. Les souches de cyanobactéries responsables de cette activité sont : Lyngbya sp., Pseudanabaena mucicola, Oscillatoria chlorina, Phormidium sp., Nostoc muscorum, Oscillatoria putrida et Microcystis aeruginosa. Les substances extracellulaires produites par les cyanobactéries étudiées ont aussi une activité antibactérienne vis-à-vis de M. luteus, Bacillus subtilis, Serratia marcescens, B. cereus, Escherichia coli 0128B12 et Staphylococcus aureus. Le biotest souris a permis de montrer que certaines cyanobactéries étudiées entraînent une mortalité des souris auxquelles sont injectées les cyanotoxines; ce qui montre que certaines souches de cyanobactéries produisent également des substances toxiques.Mots-clés : Activité antimicrobienne, cyanobactéries, écosystèmes aquatiques, substances extracellulaires, substances intracellulaires, toxicité

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

Variations saisonnières des formes de phosphores dans une station de traitement des eaux usées par lagunage, sous climat aride de Marrakech (Maroc)

L'objectif de ce travail est d'étudier dans un premier temps la dynamique du phosphore dans un système de traitement d 'eaux usées par lagunage facultatif, en relation avec les compartiments biologiques: phytoplancton, zooplancton et bactéries, dans un deuxième temps, d'évaluer, sous les conditions du climat aride, les performances épuratoires de ce système en ce qui concerne les formes du phosphore. Un intérêt particulier est porté au phénomène du relargage du phosphore par les sédiments. Les résultats montrent qu'il y a une évolution saisonnière et cyclique du phosphore dans les bassins de lagunage, en étroite corrélation avec le phytoplancton et le zooplancton. Le phytoplancton représente la part importante des formes organiques du phosphore particulaire. Les meilleures performances d'élimination du phosphore sont notées au printemps (77% pour les PO4 et 64 % pour le phosphore total). La période la moins performante est la période automne-hiver où les rendements moyens ne dépassent pas 38%. Le phosphore éliminé est stocké dans les sédiments. En période estivale, des phénomènes de relargage du phosphore à partir des sédiments ont été mis en évidence, favorisés par une zonation verticale des eaux à cette période. Des essais aulaboratoire ont montré la grande aptitude des sédiments de la station de lagunage étudiée à relarguer le phosphore, avec intervention de l'activité biologique du sédiment.Assimilation, sedimentation and release are the principal mechanisms controlling the behavior of phosphorus in aquatic ecosystems. There are numerous investigations of the phosphorus cycle in lakes and rivers in relation to the eutrophication process. There are, however, few studies about phosphorus cycling in waste stabilization ponds and most of these have discussed phosphorus removal. The aims of this paper were: 1) to study phosphorus dynamics in relation to the biomass compartment (zooplancton, phytoplancton and bacteria); and 2) to evaluate the phosphorus removal efficiency of the treatment plant under arid climatic conditions. Of particular interest was the remobilization of phosphorus from the pond sediment, both under laboratory conditions and in the field. The experimental installation consisted of two ponds receiving domestic wastewater (mean flow=120.4+5.8 m3.day-1 and specific organic load=56 kgBOD.ha-1. day-1; pond area=0.5 ha and depth=1.5 m). Samples were taken twice monthly from the surface, B1(S) and B2(S), and from the 1.5 m layers, B1(F) and B2(F). Composite (24 h) samples were taken from the inflow and the outflowof the plant to determine the removal efficiencies. In each sample, soluble reactive phosphorus (PO4), total phosphorus (PT) and total soluble phosphorus (PTD) were determined. Particulate phosphorus (PTP) was calculated as (PT-PTD) and soluble organic phosphorus (POD) as (PTD-PO4). Phosphorus release was measured in a plexiglas flask containing sediment (collected by corer from the pond bottom) overlaid with distilled water. Over 15 days, daily measurements were made of PO4 and total phosphorus. Sediment dry weight (%), volatile matter, organic carbon (%) and total phosphorus were measured before and after each test. Phosphorus contents of the phytoplankton, zooplankton and bacteria were estimated using the methods of BOUGIS (1974).The results show that cyclical and seasonal variations of phosphorus content were closely correlated with variations in the biological components. Significant correlation coefficients were noted between chlorophyll-a and particulate organic phosphorus. Organic phosphorus in algal cells was the more important form of particulate organic phosphorus. Under the arid climate, the waste stabilization ponds were more efficient at phosphate removal during the spring-summer period (77% of PO4 and 64% of total phosphorus in spring). The first pond may play the major role in phosphate removal. Phosphorus is only eliminated from stabilization ponds through accumulation in the sediment. However, part of the phosphorus which accumulates in pond sediments remains potentially mobile. During the summer period, phosphorus release from the sediment, observed in situ, was favored by stratification of the overlying water. The same phenomenon was noted during the autumn, particularly the release of POD. Laboratory studies have shown that phosphorus release may amount to 55 mg P m-2d-1. Biological activity may play a significant role in this mobilization

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

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)

Seaweed bioactive compounds against pathogens and microalgae: Potential uses on pharmacology and harmful algae bloom control

Cyanobacteria are found globally due to their adaptation to various environments. The occurrence of cyanobacterial blooms is not a new phenomenon. The bloom-forming and toxin-producing species have been a persistent nuisance all over the world over the last decades. Evidence suggests that this trend might be attributed to a complex interplay of direct and indirect anthropogenic influences. To control cyanobacterial blooms, various strategies, including physical, chemical, and biological methods have been proposed. Nevertheless, the use of those strategies is usually not effective. The isolation of natural compounds from many aquatic and terrestrial plants and seaweeds has become an alternative approach for controlling harmful algae in aquatic systems. Seaweeds have received attention from scientists because of their bioactive compounds with antibacterial, antifungal, anti-microalgae, and antioxidant properties. The undesirable effects of cyanobacteria proliferations and potential control methods are here reviewed, focusing on the use of potent bioactive compounds, isolated from seaweeds, against microalgae and cyanobacteria growth. © 2018 by the authors.Acknowledgments: This work was supported by FCT Project UID/Multi/04423/2013,by the Structured Program of R&D&I INNOVMAR—Innovation and Sustainability in the Management and Exploitation of Marine of R&D&I INNOVMAR—Innovation and Sustainability in the Management and Exploitation of Marine Resources Resources (reference NORTE-01-0145-FEDER-000035, Research Line NOVELMAR), funded by the Northern Regional Operational Program (NORTE2020) through the European Regional Development Fund (ERDF) and bCyV Mthaer +pIro(0je3c0t2 _CCVVMMaAr+RI_ I(_013_0P2_)CfuVnMdeAdRb_yI_t1h_ePp) rofugnradmedI nbteyrrtehge VpAroEgrsapman hIna—terProegrt uVg aAl ( PEOspCaTnEhPa)—20P1o4r-t2u0g2a0l

First report on cyanotoxin (Mc-lr) removal from surface water by multi-soil-layering (msl) eco-technology: Preliminary results

Cyanobacteria blooms occur frequently in freshwaters around the world. Some can produce and release toxic compounds called cyanotoxins, which represent a danger to both the environment and human health. Microcystin-LR (MC-LR) is the most toxic variant reported all over the world. Conventional water treatment methods are expensive and require specialized personnel and equipment. Recently, a multi-soil-layering (MSL) system, a natural and low-cost technology, has been introduced as an attractive cost-effective, and environmentally friendly technology that is likely to be an alternative to conventional wastewater treatment methods. This study aims to evaluate, for the first time, the efficiency of MSL eco-technology to remove MC-LR on a laboratory scale using local materials. To this end, an MSL pilot plant was designed to treat distilled water contaminated with MC-LR. The pilot was composed of an alternation of permeable layers (pozzolan) and soil mixture layers (local sandy soil, sawdust, charcoal, and metallic iron on a dry weight ratio of 70, 10, 10, and 10%, respectively) arranged in a brick-layer-like pattern. MSL pilot was continuously fed with synthetic water containing distilled water contaminated with increasing concentrations of MC-LR (0.18–10 µg/L) at a hydraulic loading rate (HLR) of 200 L m−2 day−1. The early results showed MC-LR removal of above 99%. Based on these preliminary results, the multi-soil-layering eco-technology could be considered as a promising solution to treat water contaminated by MC-LR in order to produce quality water for irrigation or recreational activities. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.This research has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 823860

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