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The removal of endocrine-disrupting xenobiotics, technical nonylphenol (NP) and 4-tert-octylphenol (OP), from aquatic environment by the cyanobacterium Planktothrix agardhii has been studied. It is shown that nonyl- and octylphenols are removed from aqueous medium in the presence of the cyanobacterium P. agardhii mainly via abiotic pathways—photolysis and hydrolysis—and biodegradation by cyanobacterial cells rather than by adsorption and accumulation in the cells. P. agardhii has a higher destructive and sorption ability for nonylphenol compared to octylphenol. The results indicate the possibility of self-purification of water bodies contaminated with alkylphenols with the participation of the mass species of cyanobacteria Planktothrix agardhii.

Winter cyanobacterial blooms have become increasingly common in eutrophic lakes advocating a need for their monitoring and risk assessment. The present study evaluated the toxicity of a winter cyanobacterial bloom in a eutrophicated freshwater lake located in Western Poland. The bloom was dominated by potentially toxic species: Planktothrix agardhii, Limnothrix redekei, and Aphanizomenon gracile. The toxin analysis revealed the presence of demethylated forms of microcystin-RR and microcystin-LR in ranges of 24.6-28.7 and 6.6-7.6 µg/L, respectively. The toxicity of sampled water was further evaluated in platelet-rich plasma isolated from healthy human subjects using lipid peroxidation and lactate dehydrogenase assays. No significant adverse effects were observed. The present study demonstrates that toxicity of some winter cyanobacterial blooms in the temperate zone, like that in Lubosińskie Lake, may not exhibit significant health risks despite microcystin production.

The occurrence of cyanobacteria in freshwaters attracts much attention due to its associated health threats and ecological implications. Yet data on the composition of cyanobacteria taxa and toxigenicity in some regions is still scarce. Here, we explored the occurrence of cyanobacteria and cyanotoxins in three locations in Ukraine (reservoir for Kasperivtsi Hydrothermal Power Plant and outflowing River Seret, and cooling pond of Khmelnytsky Atomic Power Plant) in summer 2017. Cyanobacteria were a dominant fraction at all stations. A number of potent-toxin producers were identified including Cylindrospermopsis raciborskii, Aphanizomenon gracile, Dolichospermum flos-aquae, and Planktothrix agardhii. Screening for the presence of dissolved and particulate content of microcystins (-LR, -YR, and -RR), cylindrospermopsin, and anatoxin-a yielded negative results. The studied waters displayed no toxicity in human platelets in vitro. Further toxicological and ecological studies are necessary to evaluate the potential presence of cyanotoxin producers in Ukraine.

Dinámica de un florecimiento algal otoñal en un lago hipereutrófico urbano de la región pampeana semiárida (Argentina). En este trabajo, se reporta un raro florecimiento fitoplanctónico otoñal en un lago somero de la región semiárida pampeana (Argentina). La biomasa fitoplanctónica presentó un solo pico otoñal, seguido dos meses más tarde por un pico en la clorofila. El pico de biomasa coincidió con un débil pastoreo sobre la comunidad fitoplanctónica (dominada por la poco pastoreada Planktothrix agardhii (Gomont) Anagnostidis et Komárek) junto con una reducción de la limitación por N en el otoño. El pico de clorofila ocurrió cuando las algas aumentaron su contenido de clorofila probablemente debido a la reducción de la radiación solar y la baja transparencia del agua. Esto indicará que la estacionalidad del fitoplancton en esta área particular depende de múltiples factores bióticos y abióticos. In this paper we report a rare autumm phytoplankton bloom in a shallow lake of the semiarid Pampean area of Argentina. Phytoplankton biomass peaked only once during the autumn, followed 2 months later by a chlorophyll peak. The biomass peak might have been the result of a weak grazing pressure on the phytoplankton community (dominated by the nongrazeable Planktothrix agardhii (Gomont) Anagnostidis et Komárek) coupled with a reduction in the N-limitation towards the autumm. The chlorophyll peak took place when phytoplankton cells increased their chlorophyll content probably due to a reduction of solar irradiance and low water transparency. This findings indicate that phytoplankton seasonality in this particular area may depend on multiple biotic and abiotic factors.

Harmful cyanobacteria and their cyanotoxins may contaminate drinking water resources and their effective control remains challenging. The present study reports on cyanobacterial blooms and associated cyanotoxins in the Obrzyca River, a source of drinking water in Poland. The river was examined from July to October 2019 and concentrations of microcystins, anatoxin-a, and cylindrospermopsin were monitored. The toxicity of water samples was also tested using an ecotoxicological assay. All studied cyanotoxins were detected with microcystins revealing the highest levels. Maximal microcystin concentrations (3.97 &mu, g/L) were determined in September at Uście point, exceeding the provisional guideline. Extracts from Uście point, where the dominant species were Dolichospermum flos-aquae (August), Microcystis aeruginosa (September), and Planktothrix agardhii (October), were toxic for Dugesia tigrina Girard. Microcystin concentrations (MC-LR and MC-RR) were positively correlated with cyanobacteria biovolume. Analysis of the chemical indicators of water quality has shown relationships between them and microcystins as well as cyanobacteria abundance.

Molecular studies on cyanobacteria often involve filtering and freezing of samples leading to loss of cell morphological features. Methanol is often used in preservation of biological materials in association with other fixatives. This study evaluates the application of methanol in the preservation of DNA for molecular studies as well as for the preservation of cell morphology for morphometric analysis in filamentous cyanobacteria. In the present study, both culture and environmental bloom samples were preserved using a cold methanol dehydration series (50, 70, and 100 %) and stored at −20 °C for up to 2 years. The DNA quantity and quality, nucleotide sequence retrieval, and real-time PCR quantification were analyzed over time. Morphometric cell analysis was performed on preserved samples. Results show that the DNA extracted from samples preserved up to 6 months was successfully quantified by real-time PCR. After that period, the DNA quantity decreased with the preservation time. Nevertheless, we were able to detect/amplify the target fragment in samples preserved up to 2 years. The DNA sequence and cell morphology were also maintained during the preservation time. Thus, methanol preservation is an adequate method to preserve molecular information and morphological features after long storage periods. © 2015, Springer Science+Business Media Dordrecht. This research was partially supported by the European Regional Development Fund (ERDF) through the COMPETE - Operational Competitiveness Program - and FCT - Foundation for Science and Technology national funds through projects PPCDT/AMB/67075/2006 and PEst-C/MAR/LA0015/2013, the Post-Doc research grant SFRH/BPD/75922/2011 to E. Valério and Ph.D. research grant SFRH/BD65706/2009 to C. Churro. The authors acknowledge S. Paulino from the Laboratory of Biology and Ecotoxicology of the National Institute of Health Doutor Ricardo Jorge for the assistance in the biovolume measurements.

International audience; Blooms of toxic cyanobacteria in Algerian reservoirs represent a potential health problem, mainly from drinking water that supplies the local population of Ain Zada (Bordj Bou Arreridj). The objective of this study is to monitor, detect, and identify the existence of cyanobacteria and microcystins during blooming times. Samples were taken in 2013 from eight stations. The results show that three potentially toxic cyanobacterial genera with the species Planktothrix agardhii were dominant. Cyanobacterial biomass, phycocyanin (PC) concentrations, and microcystin (MC) concentrations were high in the surface layer and at 14 m depth; these values were also high in the treated water. On 11 May 2013, MC concentrations were 6.3 μg/L in MC-LR equivalent in the drinking water. This study shows for the first time the presence of cyanotoxins in raw and treated waters, highlighting that regular monitoring of cyanobacteria and cyanotoxins must be undertaken to avoid potential health problems.

Planktothtrix agardhii (Oscillatoriales) is a filamentous cyanobacterium, which frequently forms blooms in shallow, polymictic and eutrophicated waters. This species is also a rich source of unique linear and cyclic peptides. In the current study, the profile of the peptides in samples from the P. agardhii-dominated Siemianówka Dam Reservoir (SDR) (northeast Poland) was analyzed for four subsequent years (2009–2012). The LC–MS/MS analyses revealed the presence of 33 peptides. Twelve of the most abundant ones, including five microcystins, five anabaenopeptins, one aeruginosin and one planktocyclin, were present in all field samples collected during the study. The detection of different peptides in two P. agardhii isolates indicated that the SDR population was composed of several chemotypes, characterized by different peptide patterns. The total concentration of microcystins (MCs) positively correlated with the biomass of P. agardhii. Between subsequent years, the changes in the ratio of the total MCs concentration to the biomass of P. agardhii were noticed, but they were less than threefold. This is the first study on the production of different classes of non-ribosomal peptides by freshwater cyanobacteria in Poland. Electronic supplementary material The online version of this article (doi:10.1007/s00203-014-1008-9) contains supplementary material, which is available to authorized users.

Based on current structural and statistical calculations, thousands of microcystins (MCs) can exist, yet, to date, only 246 MCs were identified and only 12 commercial MC standards are available. Standard mass spectrometry workflows for known and unknown MCs need to be developed and validated for basic and applied harmful algal bloom research to advance. Our investigation focuses on samples taken in the spring of 2018 from an impoundment fed by Oser and Bischoff Reservoirs, Indiana, United States of America (USA). The dominant cyanobacterium found during sampling was Planktothrix agardhii. The goal of our study was to identify and quantify the MCs in the impoundment sample using chemical derivatization and mass spectrometry. Modifying these techniques to use online concentration liquid chromatography tandem mass spectrometry (LC&ndash, MS/MS), two untargeted MCs have been identified, [d-Asp3, Dhb7]-MC-LR and [Dhb7]-MC-YR. [Dhb7]-MC-YR is not yet reported in the literature to date, and this was the first reported incidence of Dhb MCs in the United States. Furthermore, it was discovered that the commercially available [d-Asp3]-MC-RR standard was [d-Asp3, Dhb7]-MC-RR. This study highlights a workflow utilizing online concentration LC&ndash, MS/MS, high-resolution MS (HRMS), and chemical derivatization to identify isobaric MCs.

Cyanobacteria blooms are frequent in freshwaters and are responsible for water quality deterioration and human intoxication. Although, not a new phenomenon, concern exists on the increasing persistence, scale, and toxicity of these blooms. There is evidence, in recent years, of the transfer of these toxins from inland to marine waters through freshwater outflow. However, the true impact of these blooms in marine habitats has been overlooked. In the present work, we describe the detection of Planktothrix agardhii, which is a common microcystin producer, in the Portuguese marine coastal waters nearby a river outfall in an area used for shellfish harvesting and recreational activities. P. agardhii was first observed in November of 2016 in seawater samples that are in the scope of the national shellfish monitoring system. This occurrence was followed closely between November and December of 2016 by a weekly sampling of mussels and water from the sea pier and adjacent river mouth with salinity ranging from 35 to 3. High cell densities were found in the water from both sea pier and river outfall, reaching concentrations of 4,960,608 cells·L−1 and 6810.3 × 106 cells·L−1 respectively. Cultures were also established with success from the environment and microplate salinity growth assays showed that the isolates grew at salinity 10. HPLC-PDA analysis of total microcystin content in mussel tissue, water biomass, and P. agardhii cultures did not retrieve a positive result. In addition, microcystin related genes were not detected in the water nor cultures. So, the P. agardhii present in the environment was probably a non-toxic strain. This is, to our knowledge, the first report on a P. agardhii bloom reaching the sea and points to the relevance to also monitoring freshwater harmful phytoplankton and related toxins in seafood harvesting and recreational coastal areas, particularly under the influence of river plumes. © 2017 by the authors. Licensee MDPI, Basel, Switzerland. Acknowledgments: This work was supported by the project SNMB—INOV: Innovation for a more competitive shellfish sector co-financed by the Portuguese Government, Operational Program (OP) Mar 2020, Portugal 2020 and European Union through the European Structural Funds and Investment Funds (FEEI) and European Maritime and Fisheries Fund (EMFF). The authors also acknowledge the Centre of Marine Sciences (CCMAR), University of Algarve and Interdisciplinary Centre of Marine and Environmental Research (CIIMAR) of the University of Porto and the Funding of RD Units Strategic Plan from the Portuguese Foundation for Science and Technology (FCT) through the projects UID/Multi/04326/2013 and UID/Multi/04423/2013 respectively.

The effect of cyanobacterial blooms on the phytoplankton structure in the lowland Narew River (north-eastern Poland) was examined. The studies were carried out at stations situated at different distances from the eutrophic Siemianówka Dam Reservoir. In 2008, the investigated lowland reservoir and the outflowing river were characterized by the dominance of toxic cyanobacteria (from July to October). At a station situated 130 km below the dam, species composition in the river was very similar to that in the shallow reservoir. Planktothrix agardhii was the main and permanent dominant, both in limnoplankton and potamoplankton. The current study indicates that the eutrophic Siemianówka Dam Reservoir is the main and rich source of phytoplankton for the outflowing Narew River. Cyanobacteria were dominant in the river phytoplankton at all sampling stations, but their share in phytoplankton biomass gradually decreased with the distance from the dam. Chemical analysis revealed the presence of microcystins (MCs) in water samples collected from June to October. The toxins, mainly demethylated MC analogues, were detected at a long distance down the river, even 100 km from the dam. Maximum concentration of MCs (14.3 μg l−1) was measured on 13 October, 9.1 km below the dam.

Two homotyrosine-bearing cyanopeptolins are described from Planktothrix agardhii CYA 126/8. The compounds feature a common homotyrosine-containing cyclohexadepsipeptide and differ by sulfation of an exocyclically located 2-O-methyl-d-glyceric acid residue. In addition we describe two anabaenopeptins, which contain two homotyrosine residues, one of which is N-methylated. The anabaenopeptins have a common cyclopentapeptide portion and differ in the amino acid linked to it via an ureido bond, arginine and tyrosine, respectively.

For the first time in the Czech Republic, the PAX-18 coagulant has been used to restore a eutrophic fishpond. The polyaluminium hydrochloride coagulant was applied repeatedly to a shallow eutrophic fishpond in spring 2005. Two cylindrical plastic enclosures were used to isolate parts of the pond as untreated controls. Selected environmental variables were measured in situ. Water samples were analyzed regularly for nutrients, chlorophyll a concentration and phytoplankton abundance and structure with special focus on Planktothrix agardhii. The PAX-18 treatment led to a marked increase in the N/P ratio and changes in the structure and abundance of phytoplankton in the fishpond and P. agardhii blooms were eliminated in the fishpond. By contrast, P. agardhii dominated the phytoplankton in the control enclosures, as it had in the fishpond in 2004, prior to the PAX-18 treatment.

Temporal and spatial variation in the concentrations of intra- and extra-cellular microcystins were studied in a hypertrophic lake with bloom of Planktothrix agardhii (Gomont) Anagnostidis et Komarek. Concomitantly with increase in water temperature (from 2 to 20 °C) abundance of P. agardhii increased from 1.9 x 10 5 to 4.3 x 10 7 trichomes L -1 . In autumn, in spite of temperature lower (14°C) than in summer it was still very high. Mass development of P. agardhii (to 6 x 10 6 L -1 and higher) caused a severe decrease in water transparency (to 0.5 - 0.2 m in summer/autumn). The cyanobacterium density was relatively uniform within water column; only in summer (July) it was significantly higher (by about 30%) in surface than in bottom layer. From spring to autumn microcystins (MCs) were mainly biomass-bound (up to 90 μg MC-LR equiv. L -1 ), whereas the level of extra-cellular toxins was much lower (up to 2 μg L -1 ) and relatively stable. Only in winter, high amounts of MCs (11.3 μg L -1 ) were released from decaying biomass into water. The increasing concentrations of biomass-bound microcystins in the lake water positively correlated (R 2 = 0.9863; y = -0.1285x 2 + 7.14x ) with the abundance of P. agardhii and the highest concentrations of the intracellular MC fraction were found during the exponential phase of P. agardhii growth. In addition, the surface-sampled biomass of P. agardhii contained in autumn 2-fold more MCs (2.75 μg MC-LR equiv. per 10 6 P. agardhii trichomes) than the bottom-sampled one (1.41 μg MC-LR equiv. per 10 6 trichomes). This is the first report showing that despite the homogenous distribution of P. agardhii in water column of a shallow lake, various seasonal and spatial distributions of both extra-cellular and intracellular fractions of microcystins occur.

Cyanobacteria are phytoplanktonic organisms widely occurring in freshwaters, being frequently associated with the production of toxins, namely microcystins (MCs). MCs are produced non-ribosomally by a multienzyme complex (mcy genes). It has been reported that environmental factors, such as light intensity, can influence toxin production. The aim of this study was to assess the influence of light intensity in the transcription of the mcyA gene and corresponding production of microcystins in toxic isolates of Planktothrix agardhii, where little is known, and compare them to Microcystis aeruginosa. For that purpose, cultures were exposed to three different light intensities (4, 20 and 30 μmol photons m-2 s-1) for 18 days at 20 ± 1 °C. The growth was followed daily using absorbance readings. Samples were collected at each growth stage for cell counting, microcystins quantification and RNA extraction. The level of transcripts was quantified by RT-qPCR and the relative expression determined using 16S rDNA, gltA and rpoC1 as reference genes. The most stable reference genes in M. aeruginosa were rpoC1 and gltA, whereas in P. agardhii were 16S rDNA and gltA. There was a correspondence between the growth rate and light intensity in M. aeruginosa and P. agardhii. The growth rates for both species were lower at 4 and higher at 30 μmol photons m-2 s-1. Microcystin concentration per cell was similar between light intensities in M. aeruginosa and over time, while in P. agardhii it was higher in the stationary phase at 4 μmol photons m-2 s-1. There were differences in the expression of mcyA between the two species. In M. aeruginosa, the highest levels of expression occurred at 4 μmol photons m-2 s-1 in the adaptation phase, whereas for P. agardhii it was at 4 μmol photons m-2 s-1 in the exponential growth phase. Our results indicate that the light intensities tested had distinct influences on the growth, microcystin production and mcyA expression levels, presenting considerable differences in M. aeruginosa and P. agardhii. © 2016 Elsevier This research was partially supported by the European Regional Development Fund (ERDF) through the COMPETE – Operational Competitiveness Program – and FCT — Foundation for Science and Technology national funds through Ph.D research grant SFRH/BD65706/2009 to C. Churro and Post-Doc research grant SFRH/BPD/75922/2011 to E. Valério. The authors thank Sérgio Paulino for the assistance in the microcystins quantifications with ELISA kit and Carina Menezes for the HPLC evaluations.

International audience; Natural leaf litter inputs is one factor that may help to minimize the likelihood of excessive algal growth. We tested the allelopathic effect of the grey willow (Salix atronicerea) on two phytoplankton species: Planktothrix agardhii (toxic and non-toxic cyanobacterial strains) and Scenedesmus communis (a chlorophyte). Effect was evaluated by combining leaf extracts and pulse amplitude modulation (PAM) chlorophyll fluorescence yield to measure photosynthetic activity responses. Phototrophic growth of the cyanobacterial species was suppressed even at very low concentrations of the extract while growth of the chlorophyte species was not affected. In the two cyanobacteria strains, inhibition of the chlorophyll fluorescence yields was significantly higher in the microcystin-free strain. Polyphenols are suspected to cause oxidative damage to cyanobacteria and thereby induce selective growth inhibition, similarly to hydrogen peroxide treatments against harmful cyanobacteria. Our results evidence willow extract or exudate as a promising agent selectively affecting cyanobacterial growth, but further studies are needed to determine the environmental impact and the inhibiting process. © 2016 Elsevier B.V.

Cyanobacteria produce a large number of bioactive oligopeptides with yet unknown functions. Here the effect of environmental factors on the production of two anabaenopeptins and a microviridin by Planktothrix agardhii was investigated. The results were compared with previous findings on the production of a third family of oligopeptides, the highly toxic microcystins, to test the hypothesis that environmental factors affect the production of different types of cyanobacterial bioactive oligopeptides in a similar manner. Despite marked changes in culture conditions, variations in the amount of cell-bound anabaenopeptins and microviridin I per biomass unit did not exceed a factor of 5. High amounts of cell-bound anabaenopeptins and microviridin I per Planktothrix biovolume were associated with a high availability of nitrogen and phosphorus. The production of anabaenopeptins and microviridin continued as long as the Planktothrix cultures grew. In all cases the oligopeptide net production rate was linearly correlated to the growth rate of Planktothrix, identifying the growth activity as a major regulator of anabaenopeptin and microviridin production. The concentration of anabaenopeptins and microviridins in nature may therefore be estimated from the biomass concentration of their producers. These findings are similar to those previously reported for microcystins and thus support the idea that different types of bioactive cyanobacterial oligopeptides may share common regulation patterns. This may be seen as a hint to a mutual function of cyanobacterial oligopeptides, although further studies are needed to draw final conclusions on this issue.

The effects of nutrient conditions on the growth and intracellular nitrogen and phosphorus quotas of filamentous Cyanobacteria Planktothrix agardhii, isolated from eutrophic El Kansera waters were studied in batch culture. The deficiency in nitrogen affects the biomass more severely than the deficiency in phosphorus, with more marked effects on chlorophyll a content. Intracellular nitrogen (QN) and phosphorus (QP) quotas, determined experimentally, show that this alga is capable of storing quantities of N and P, which explains the delay observed between the onset in deficiency of the culture and the stoppage of growth. The values of QN, of QP, as well as those of QChl (chlorophyll a contents by filament) vary between a minimum (Q0) and a maximum (Qm) that correspond to a situation of deficiency and a nutritive supply respectively. The resumption of growth after the addition of the limiting element is discussed in relation to the added initial dose and to the instantaneous nitrogen and phosphorus ...

We exposed water samples from a recreational lake dominated by the cyanobacterium Planktothrix agardhii to different concentrations of hydrogen peroxide (H2O2). An addition of 0.33 mg·L-1 of H2O2 was the lowest effective dose for the decay of chlorophyll-a concentration to half of the original in 14 h with light and 17 h in experiments without light. With 3.33 mg·L-1 of H2O2, the values of the chemical oxygen demand (COD) decreased to half at 36 and 126 h in experiments performed with and without light, respectively. With increasing H2O2, there is a decrease in the total and faecal coliform, and this effect was made more pronounced by light. Total and faecal coliform were inhibited completely 48 h after addition of 3.33 mg·L-1 H2O2. Although the densities of cyanobacterial cells exposed to H2O2 did not decrease, transmission electron microscope observation of the trichomes showed several stages of degeneration, and the cells were collapsed after 48 h of 3.33 mg·L-1 of H2O2 addition in the presence of light. Our results demonstrate that H2O2 could be potentially used in hypertrophic systems because it not only collapses cyanobacterial cells and coliform bacteria but may also reduce chlorophyll-a content and chemical oxygen demand., Facultad de Ciencias Exactas, Facultad de Ciencias Naturales y Museo

A species-specific method to detect and quantify Planktothrix agardhii was developed by combining the SYBR Green I real-time polymerase chain reaction technique with a simplified DNA extraction procedure for standard curve preparation. Newly designed PCR primers were used to amplify a specific fragment within the rpoC1 gene. Since this gene exists in single copy in the genome, it allows the direct achievement of cell concentrations. The cell concentration determined by real-time PCR showed a linear correlation with the cell concentration determined from direct microscopic counts. The detection limit for cell quantification of the method was 8 cells μL(-1), corresponding to 32 cells per reaction. Furthermore, the real-time qPCR method described in this study allowed a successful quantification of P. agardhii from environmental water samples, showing that this protocol is an accurate and economic tool for a rapid absolute quantification of the potentially toxic cyanobacterium P. agardhii.

Cyanobacteria are a diverse well adapted group of organisms that presents amazing morphological diversity. Cyanobacteria can be unicellular or colonial (filamentous, spherical or amorphous) (Fig. 1). Since cyanobacteria have cells larger than normal bacterial cells and behavior more similar to algae, they were classified under the microalgae for a long time and acquire the name of blue-green algae or Cyanophyta (Whitton & Potts 2000). Cyanobacteria is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from their coloration (cyano = blue). The vegetative cell wall is of Gram-negative type and in some species the peptidoglycan layer is considerably thicker than in other bacteria. Many unicellular and filamentous cyanobacteria possess an “envelope” outside the lipopolysaccharide (LPS) “outer membrane”, which is called: sheath, glycocalyx, or capsule, and depending on the consistency, gel, mucilage or slime. The sheaths of cyanobacteria are predominantly polysaccharide, but a part of its weight may be polypeptides, and depending on the species, some types of sugar residues may be involved (Castenholz, 2001).

The concentration of microcystins (MCs) produced during blooms depends on variations in both the proportion of strains containing the genes involved in MC production and the MC cell quota (the ratio between the MC concentration and the density of cells with the mcyA genotype) for toxic strains. In order to assess the dynamics of MC-producing and non-MC-producing strains and to identify the impact of environmental factors on the relative proportions of these two subpopulations, we performed a 2-year survey of a perennial bloom of Planktothrix agardhii (cyanobacteria). Applying quantitative real-time PCR to the mcyA and phycocyanin genes, we found that the proportion of cells with the mcyA genotype varied considerably over time (ranging from 30 to 80% of the population). The changes in the proportion of cells with the mcyA genotype appeared to be inversely correlated to changes in the density of P. agardhii cells and also, to a lesser extent, to the availability of certain nutrients and the abundance of cladocerans. Among toxic cells, the MC cell quota varied throughout the survey. However, a negative correlation between the MC cell quota and the mcyA cell number during two short periods characterized by marked changes in the cyanobacterial biomass was found. Finally, only 54% of the variation in the MC concentrations measured in the lake can be explained by the dynamics of the density of cells with the MC producer genotype, suggesting that this measurement is not a satisfactory method for use in monitoring programs intended to predict the toxic risk associated with cyanobacterial proliferation.

International audience; The factors that control the production of microcystins (hepatotoxins) during cyanobacterial blooms, and the function of these metabolites remain largely unknown. In an attempt to provide answers to these questions, we compared the fitness of microcystin (MC)-producing and non-MC-producing Planktothrix agardhii strains under various experimental conditions. More specifically, we investigated the effects of temperature, light intensity and nitrate concentrations on several MC-producing and non-MC-producing strains in monoculture and competition experiments. In the monoculture experiments, no significant difference in cell growth rates was found for any of the environmental conditions tested. On the other hand, at the end of the competition experiments, we found that when the environmental conditions limited cell growth, MC-producing strains were clearly winning out over the non-MC-producing ones. This suggested that, under growth-limiting conditions, the benefits of producing MC outweigh the cost. Moreover, the reverse was found under non-growth-limiting conditions, suggesting that under environmental conditions that favour cyanobacterial growth, the cost of MC production must outweigh its benefits. These findings suggest that environmental factors may have an indirect effect on the MC production rate, and on the selection of MC-producing and non-MC-producing strains, via their direct impact on both the cell growth rate and the cell densities in the cultures. Several hypotheses have been advanced concerning the possible function of MCs, but none of them seems to be supported by our data.

International audience; The role of zooplankton in the control of cyanobacterial blooms and the transfer of cyanotoxins to higher trophic levels are of great importance to the management of water resources. Many studies have focused on the cyanobacterium Microcystis, but few have examined the interactions between zooplankton and filamentous cyanobacteria. In this study, we provide experimental evidence for the potential grazing of two toxic strains of filamentous cyanobacteria, Planktothrix rubescens and P. agardhii, by Daphnia pulicaria, and for transfer of toxins in the planktonic food chain. We determined clearance rates (CRs) by adult and juvenile D. pulicaria of the two Planktothrix strains, Scenedesmus acutus and a mixture of S. acutus cells with P. rubescens culture filtrate. Filament lengths were analyzed, and microcystin (MCY) presence in Daphnia was assessed using the Protein Phosphatase-2A (PP-2A) Inhibition Assay. The two Planktothrix strains were equally grazed by D. pulicaria, but at lower CRs than S. acutus. Potential anti-grazer toxins in P. rubescens filtrate did not inhibit Daphnia grazing. Small P. rubescens (< 100 mu m) filaments were preferentially grazed by adult D. pulicaria, suggesting their limited ability to control a Planktothrix population during a bloom. Large quantities of MCYs were found in unstarved Daphnia previously exposed to Planktothrix, whereas quantities were significantly smaller in individuals starved for 24 h before preservation. This indicated a potential for transfer of toxins in the food chain by Daphnia, especially immediately after ingestion of toxic cyanobacteria.

Single filaments of Planktothrix spp. were isolated from laboratory cultures of P. agardhii (NIES 595) and P. rubescens (SL 03) and from four freshwater lakes in England and Turkey. Filament lengths were measured and microcystins were extracted by freeze-thawing and boiling. Microcystin analysis of the isolated single filaments was performed by ELISA using antibodies raised against microcystin-LR with a minimum detection limit (MDL) of 11 pg filament −1 . In some cases a high percentage of the filaments from the environmental samples and laboratory cultures were below the MDL of the assay. Based on the filaments with detectable microcystin contents, P. agardhii from Bassenthwaite Lake (England) had the lowest mean microcystin concentration (0.7 fg μm −3 ), and the highest microcystin concentration (2.9 fg μm −3 ) was measured in P. rubescens from Iznik Lake (Turkey). We investigated the relationship for filaments with microcystin contents above MDL and their biovolume. Relationships varied widely although P. agardhii from Bassenthwaite showed a better (positive) relationship between filament biovolume and microcystin content than P. rubescens from environmental samples. Under culture conditions, P. rubescens showed a good relationship between filament biovolume and toxin content.

Samples from a total of 134 lakes, practically all freshwater lakes in Aland, SW Finland, were screened for microcystins, hepatotoxic peptides of cyanobacteria, using high performance liquid chromatography (HPLC), time-resolved fluoroimmunoassay (TR-FIA), and protein phosphatase inhibition (PPIA) during two summers. Microcystins were recorded in 4 of 54 lakes in 1999 and 14 of 134 lakes in 2000, especially in eutrophic lakes but also in some dystrophic lakes and one oligotrophic. There was a satisfactory agreement between results obtained with different methods. The most likely microcystin-producers involved, as judged by microscopical examination, were Planktothrix agardhii, Microcystis aeruginosa, and Anabaena lemmermannii. One drinking-water reservoir and several lakes used for irrigation were microcystin-positive. Microcystins were also detected in late autumn samples from some eutrophic lakes.