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This study investigates the capability of a Bacillus flexus strain isolated from decayed cyanobacterial blooms for the bioremediation of Cylindrospermopsis raciborskii and cylindrospermopsin (CYN) toxin. The algicidal activity of this strain was tested by co-cultivation with C. raciborskii cultures. CYN biodegradation was investigated in the presence of living and heat-inactivated bacterial cells or bacterial filtrate. Living bacterial cells inhibited C. raciborskii growth after 2 days of incubation with complete cell death at day 5. Bacterial filtrate caused a rapid reduction in C. raciborskii growth at the first day, with complete cell lysis at day 3. Only living cells of SSZ01 caused reduction in CYN released into the medium during the bacterial decay of C. raciborskii cells. The biodegradation rate of CYN by SSZ01 relied on initial toxin concentrations. The highest rate (42 μg CYN L−1 day−1) was obtained at the higher initial concentration (300 μg L−1), and the lowest (4μg CYN L−1 day−1) was at lower concentration (50 μg L−1). These results suggest that this bacterial strain could be employed to bioremediate cyanobacterial blooms in freshwaters. Also, the application of this bacterium in slow sand filters would give possibilities for degradation and bioremediation of cyanotoxins in drinking water treatment plants.

Cylindrospermopsin (CYN) is a cyanotoxin that has raised serious concerns about public health in many parts of the world. It can bioaccumulate and affect the health of aquatic organisms, but despite this, few studies have been conducted on CYN uptake and clearance in fish. In this paper, the authors evaluate the uptake and clearance of CYN in the muscle tissue and viscera of juvenile tilapia (Oreochromis niloticus) after exposure to aqueous extracts and whole cells of Cylindrospermopsis raciborskii (CYN-producer). CYN blended with commercial fish food, and three experiments were conducted. In the first trial, fish food, and aqueous extracts containing 0.31 μg CYN g-1 of food per day, was administered to tilapia for 15 days. In the second trial, fish were provided food and intact cells (5.4 μg CYN g-1 of food per day) for 15 days. In the last trial, they were provided fish food and aqueous extracts (0.8 μg CYN g-1 of food per day) for 12 days, and for the next 10 days, the animals were fed food without toxic cell extracts (to simulate a clearance period). The concentration of CYN in muscle tissue and viscera was analysed using ELISA. In the case of juvenile tilapia, the presence of CYN was higher in viscera than in muscle tissue, and the toxin remained in the tissues even after 10 days without the addition of contaminated food. The results suggest that tilapia represents a potential source of CYN transfer through the food web, and this shows the need for a continuous monitoring of this compound in organisms that are used for human and animal consumption.

Impact of macrophyte Lemna trisulca on the growth rate and synthesis of cylindrospermopsin (CYN) by cyanobacterium Raphidiopsis raciborskii was determined. The presence of L. trisulca inhibited the biomass accumulation of the cyanobacterium by 25% compared to the control during co-cultivation. The simultaneous cultivation of these organisms slightly affected the inhibition of macrophyte growth rate by 5.5% compared to the control. However, no morphological changes of L. trisulca after incubation with cyanobacteria were observed. It was also shown that the long-term (35 days) co-cultivation of R. raciborskii and L. trisulca led to a decrease in CYN concentration in media and cyanobacterial cells by 32 and 38%, respectively, compared to the values obtained for independent cultivation of cyanobacterium. Excessive absorption of phosphate ions by L. trisulca from the medium compared to nitrate ions led to a significant increase in the nitrate:phosphate ratio in the media, which inhibits the development of cyanobacterium. The obtained results indicate that L. trisulca in the natural environment may affect the physiology of cyanobacteria. The presented study is the first assessment of the allelopathic interaction of macrophyte and R. raciborskii.

The occurrence of toxic cyanobacteria in surface waters and their impact on drinking water treatment plants (WTPs) is a growing, global concern. The main objective of this paper was to assess the presence of cyanobacteria in surface water sources and associated cell removal efficiency in full-scale WTPs across the world. Previously unpublished data was collected from WTPs experiencing cyanobacterial blooms in either their managed surface waters or recreational waters. In total, data were collected from 31 surface water sources and 21 WTPs in North and South America, Europe, Asia, and Australia. The most commonly detected species were identified in both the surface waters, including Microcystis, Anabaena, Nostoc, Oscillatoria, and Planktolyngbya, and water treatment plant intakes, including Microcystis, Cylindrospermopsis, Anabaena, Pseudanabaena, and Aphanizomenon. In the intakes, cyanotoxins and taste and odor (T&O) compounds frequently co-occurred (80%) as did multiple cyanotoxins (39%). Conventional treatment saw a wide range of removal depending on the density of cells, species, and metabolites. Although more than 28% of sampling events displayed negligible or even negative removals of metabolites or cells due to accumulation within the clarifier, filtration, or water recycling, the presence of multiple treatment barriers, particularly advanced treatments like granular activated carbon and nanofiltration, allowed for the cells and their metabolites of concern to be removed to below guideline values. During treatment, total microcystins were often removed without releasing their intracellular fraction, whereas cylindrospermopsin, geosmin, and 2-MIB were commonly detected as entirely extracellular at the plant's intake. The maximum tolerable cell (MTC) counts for cyanotoxin- or T&O-producing cells were calculated using guideline values, average removal efficiency, and the average cell quota derived from data. The 21 WTPs in this work were found to be able to tolerate approximately 74,000 cells/mL for microcystins, 8,000 cells/mL for cylindrospermopsin, and 1,200 cells/mL for geosmin and 2-MIB before exceeding guideline values. These levels provide guidance for water treatment plant operators to assess the potential risk associated with cells capable of producing cyanotoxins or T&O compounds. Highlights Distinguish between the abundance and presence of cyanobacteria.; Assess the performance of a full-scale treatment process for the successful removal of cyanobacteria and their associated metabolites.; Determine the range of cyanotoxin or T&O compound concentration per cell.

is a harmful bloom-forming cyanobacterium with strains that vary in ecophysiology within and between populations around the world. Understanding the extent of intraspecific diversity of strains is ...

Blooms of toxin-producing cyanobacteria have been more frequent and lasting because of the eutrophication of freshwater ecosystems, including those used for aquaculture. The aim of the present study was to investigate the effects of chronic exposure to a saxitoxin-producing strain of Raphidiopsis (Cylindrospermopsis) raciborskii on the performance of Nile tilapia (Oreochromis niloticus) fingerlings over a 60-d period. The fingerlings were cultivated under the following conditions: 1) water without cyanobacterium (WATER), 2) R. raciborskii in ASM-1 culture medium (CYANO), and 3) ASM-1 culture medium without cyanobacterium (ASM). Exposure to the CYANO treatment led to a significant increase in the mortality rate (p 0.05). Saxitoxin toxicity was dependent on the weight of the fingerling (p

Phosphorus (P) is responsible for algal growth and the structural changes in algal communities. Therefore, it is essential to know whether the different phosphorus availability to different algae can change the community structure. In this study, the interspecific competition was investigated at two bloom-forming cyanobacterium, Cylindrospermopsis raciborskii and Microcystis aeruginosa, when both were treated with five different phosphate compounds, including K2HPO4, β-glycerol phosphate, (2-aminoethyl)-phosphinic acid, glyphosate, and P-free. The results of mono-culture experiments showed that the two species could utilize the dissolved organic phosphorus (DOP) and K2HPO4 (DIP) as the sole P resource. Moreover, the specific growth rates and the endogenous alkaline phosphatase activity in M. aeruginosa cells were much lower than those in C. raciborskii under DOP and DIP treatments. In the co-cultured experiments, however, a significant biomass increase in C. raciborskii was observed in all experimental P treatments, except for glyphosate, regardless of its initial cell density proportion. A 31.8–63.4% increase in cell number of C. raciborskii was found after incubated into K2HPO4, while the highest biomass of mixed samples, 17.72 × 106 cell mL−1, was observed in the (2-aminoethyl)-phosphinic acid treatment (50C50M). Additionally, higher specific growth rate was also found in C. raciborskii when compared with M. aeruginosa under P-free; the increasing proportion of C. raciborskii were 29.1% (50C50M), 16.4% (75C25M), and 36.7% (25C75M), respectively. When the mixed samples were co-cultivated under glyphosate, C. raciborskii cells appeared to be depressed, whereas the cell density of M. aeruginosa increased rapidly. The findings indicated that an excellent P competition might give some advantages for C. raciborskii dominance in natural waters with DIP limitation or DOP abundance.

Cyanobacteria stand out among phytoplankton when they form massive blooms and produce toxins. Because cyanotoxin genes date to the origin of metazoans, the hypothesis that cyanotoxins function as a defense against herbivory is still debated. Although their primary cellular function might vary, these metabolites could have evolved as an anti-predator response. Here we evaluated the physiological and molecular responses of a saxitoxin-producing Raphidiopsis raciborskii to infochemicals released by the grazer Daphnia gessneri. Induced chemical defenses were evidenced in R. raciborskii as a significant increase in the transcription level of sxt genes, followed by an increase in saxitoxin content when exposed to predator cues. Moreover, cyanobacterial growth decreased, and no significant effects on photosynthesis or morphology were observed. Overall, the induced defense response was accompanied by a trade-off between toxin production and growth. These results shed light on the mechanisms underlying zooplankton–cyanobacteria interactions in aquatic food webs. The widespread occurrence of the cyanobacterium R. raciborskii in freshwater bodies has been attributed to its phenotypic plasticity. Assessing the potential of this species to thrive over interaction filters such as zooplankton grazing pressure can enhance our understanding of its adaptive success.

Cyanotoxins from toxic blooms in lakes or eutrophic reservoirs are harmful to several organisms including zooplankton, which often act as vectors of these secondary metabolites, because they consume cyanobacteria, bioaccumulate the cyanotoxins and pass them on along the food chain. Microcystins are among the most commonly found cyanotoxins and often cause zooplankton mortality. Although cyanobacterial blooms are common and persistent in Mexican water bodies, information on the bioaccumulation of cyanotoxins is scarce. In this study we present data on the bioaccumulation of cyanotoxins from Planktothrix agardhii, Microcystis sp., Cylindrospermopsis raciborskii and Dolichospermum planctonicum blooms in the seston (suspended particulate matter more than 1.2 μm) by zooplankton and fish (tilapia (Oreochromis niloticus) and mesa silverside (Chirostoma jordani) samples from Lake Zumpango (Mexico City). The cyanotoxins were extracted from the seston, zooplankton and fish tissue by disintegration using mechanical homogenization and 75% methanol. After extraction, microcystins were measured using an ELISA kit (Envirologix). Concentration of microcystins expressed as equivalents, reached a maximum value of 117 μg g−1 on sestonic samples; in zooplankton they were in the range of 0.0070–0.29 μg g−1. The dominant zooplankton taxa included Acanthocyclops americanus copepodites, Daphnia laevis and Bosmina longirostris. Our results indicate twice the permissible limits of microcystins (0.04 μg kg−1 d−1) for consumption of cyanobacterial products in whole fish tissue of Chirostoma jordani. The data have been discussed with emphasis on the importance of regular monitoring of water bodies in Mexico to test the ecotoxicological impacts of cyanobacterial blooms and the risk that consumption of products with microcystins could promote.

Interactions between macrophytes and phytoplankton have been studied extensively in temperate water bodies, but far less attention has been paid to those for emergent macrophytes in the tropics. We investigated the effects of six emergent macrophyte species (Brachiaria mutica, Ipomoea aquatica, Sphagneticola trilobata, Ludwigia adscendens, Pandanus amaryllifolius and Persicaria barbata) on the phytoplankton community of a tropical reservoir using ex situ experiments with multiple planting densities (Treatment 1: 0.108, Treatment 2: 0.24, Treatment 3: 0.40, Treatment 4: 0.58 g dry weight L−1) in 100-L mesocosms. Chlorophyll a (as a proxy of total phytoplankton biomass) and phytoplankton community structure were examined. The initial phytoplankton community (average chlorophyll a: 20.36 ± 0.69 µg L−1) was dominated by cyanobacteria: Planktolyngybya, Pseudanabaena and Cylindrospermopsis (average relative biovolume 0.68 ± 0.03). Over four weeks, L. adscendens (Treatments 3 and 4) and P. barbata (Treatments 2 to 4) significantly reduced chlorophyll a concentrations by 3.29–6.69 µg L−1 compared to the controls. Comparing species effects over four weeks for Treatment 4, P. barbata significantly lowered chlorophyll a concentrations compared to I. aquatica while there were no significant differences between all other species. All treatments of L. adscendens and P. barbata significantly reduced the relative biovolume of cyanobacteria in the phytoplankton communities by 0.19–0.39 compared to the controls. The highest-density treatments of all six macrophyte species led to significant shifts in the phytoplankton community structure by reducing the relative abundance of filamentous cyanobacteria (Planktolyngbya, Pseudanabaena) and/or increasing the relative abundance of cryptomonads (Chroomonas, Rhodomonas). This study shows the potential of emergent macrophyte species, especially L. adscendens and P. barbata, to reduce total phytoplankton biomass and cyanobacterial dominance in tropical water bodies, and a range of plant densities which were effective.

Cyanobacterial blooms are intensifying global ecological hazards. The fine structure and dynamics of bloom community are critical to understanding bloom development but little understood. Here, the questions whether dominant bloomers have high diversity and whether dominant OTUs (operational taxonomical units) compete with one another were addressed. 16S rRNA gene amplicons from an annual bloom at five locations in Harsha Lake (Ohio, USA) showed cyanobacteria were the dominant phylum, and co-existing major bacterial phyla included Proteobacteria, Bacteroidetes, Actinoacteria, and Verrucomicrobia. On the genus level, the initial dominance by Dolichospermum in June yielded to Planktothrix in July, which were replaced by Microcystis and Cylindrospermopsis in August throughout the bloom. Based on the number of verified unique OTUs (a within-genus biodiversity metric), dominant genera tended to have high within-genus diversity. For example, Dolichospermum had 57 unique OTUs, Planktothrix had 36, Microcystis had 12, and Cylindrospermopsis had 4 unique OTUs. Interestingly, these different OTUs showed different dynamics and association with other OTUs. First, no between-OTU competitions were observed during the bloom cycle, and dominant OTUs were abundant throughout the bloom. Such biodiversity of OTUs and their dynamics were verified in Microcystis aeruginosa with two microcystin synthetase genes (mcyA and mcyG): the relative abundance of both genes varied during the bloom based on quantitative PCR. Two Dolichospermum circinale OTUs and one P. rubescens OTU were most abundant and persistently present throughout the entire bloom. Second, these OTUs differed in the OTUs they were associated with. Third, these OTUs tended to have different levels of association with the environmental factors, even they belonged to the same genera. These findings suggest the structure and dynamics of a cyanobacterial bloom community is complex, with only few OTUs dominating the bloom. Thus, high-resolution molecular characterization will be necessary to understand bloom development.

Koka Reservoir in Ethiopia has been severely impacted by water quality deterioration associated with harmful algal blooms. As a large proportion of the annual nutrient budget of the reservoir is believed to be of riverine origin, nutrient availability is presumably largely influenced by rainfall pattern and hydrological cycles, which are related to changes in climatic conditions such as El Nino-induced drought. The effect of El Nino-induced drought, which occurred in 2015, on the cyanobacterial community structure of Koka Reservoir was, therefore, investigated from May 28, 2015 to April 28 2016. The drought caused the failure of the main rainy season, which expectedly caused reduction in the external input of nutrients and changes in other limnological conditions of the reservoir. These changes, particularly nitrogen limitation, triggered the unusual dominance of the diazotrophic cyanobacterial genus Cylindrospermopsis over the previously persistently dominant nondiazotrophic genus, Microcystis, in the reservoir.

Aphanizomenonaceae is a recently proposed family of Cyanobacteria encompassing 12 planktic genera. The formation and distribution of heterocytes and akinetes along the trichome are the main morphological characteristics of this family. In this context, Sphaerospermopsis and Cylindrospermopsis are close related genera both molecularly and morphologically differing by 1) rounded akinetes adjacent to the heterocytes disposed along the trichome in Sphaerospermopsis; 2) apical heterocytes and akinetes separated by a few cells (2–3) in Cylindrospermopsis. Recently, during a survey on cyanobacteria from tropical Brazilian eutrophic lakes, strains with similarities to Sphaerospermopsis and Cylindrospermopsis were isolated. Aiming to elucidate the phylogenetic placement of these strains, we performed morphological, physiological and molecular studies. The Brazilian strains were confirmed to be closely related to Sphaerospermopsis and Cylindrospermopsis, but the phylogeny, based on 16S rRNA gene and 16S–23S rRNA intergenic region, clustered them in a well-defined clade separate from these genera. According to these results, we detailed the morphology, physiology, and phylogeny of the proposed new genus Amphiheterocytum, which showed potential to create blooms in tropical shallow lakes.

Anthropogenic disturbances within or near aquatic ecosystems often contribute to eutrophication events. Cyanobacteria are a key group responsible for environmental problems associated with eutrophication processes. Interest is growing in estimating the threat of cyanobacteria in tropical Africa, however, there is still a lack of understanding regarding temporal drivers of cyanobacteria dynamics in natural aquatic ecosystems given the paucity of relevant fundamental research in this area. To better understand cyanobacteria dynamics, potential drivers of cyanobacteria dynamics were investigated in a model tropical reservoir system, whereby phytoplankton communities and water quality parameters were sampled during the tropical hot-wet, cool-dry and hot-dry seasons. Fifteen cyanobacteria taxa were recorded over the study period. Microcystis spp. and Cylindrospermopsis spp., known cyanotoxins producers, were the most prevalent bloom-forming taxa found in the study, with overall Cyanobacteria relative abundances being greatest during the cool-dry season. This was likely driven by decreased river inflows and increased reservoir mixing during the cool-dry period. Combinations of macrophyte cover, dissolved oxygen levels, water transparency, reactive phosphorus, water depth and chemical oxygen demand were found to significantly affect cyanobacteria community structure. The study highlights that under climate change forecasts (for much of tropical arid Africa), potentially harmful and problematic algal species may proliferate. Management options, therefore, need to be explored to maintain water quality and potable availability to mitigate against indirect harmful effects of environmental changes on ecosystems and human communities that utilise their services.

The geographical range of invasive cyanobacteria with high toxigenic potential is widening because of eutrophication and global warming, thus, monitoring their appearance is necessary for safe water quality control. Most invasive cyanobacteria are nostocalean species, and their accurate identification by classical morphological methods may be problematic. In this study, we developed polymerase chain reaction (PCR) primers to selectively identify five invasive cyanobacterial genera, namely, Chrysosporum, Cuspidothrix, Cylindrospermopsis, Raphidiopsis, and Sphaerospermopsis, using genetic markers such as rbcLX, rpoB, rpoC1, and cpcBA, and determined the amplification conditions for each pair of primers. The primer performances were verified on single or mixed nostocalean cyanobacterial isolates. The five primers allowed selective identification of all the target genera. In field samples collected during summer, when cyanobacteria flourished in the Nakdong River, the respective PCR product was observed in all samples where the target genus was detected by microscopic analysis. Besides, weak bands corresponding to Sphaerospermopsis and Raphidiopsis were observed in some samples in which these genera were not detected by microscopy, suggesting that the cell densities were below the detection limit of the microscopic method used. Thus, the genus-specific primers developed in this study enable molecular monitoring to supplement the current microscopy-based monitoring.

Made available in DSpace on 2022-04-28T19:46:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-03-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Toxic cyanobacteria blooms are a frequent problem in subtropical reservoirs and freshwater systems. The purpose of this study was to investigate the occurrence of potentially toxic cyanobacteria and the environmental conditions associated with the presence of cyanotoxins in a Brazilian subtropical reservoir. Five collections were carried out at seven sampling locations in the reservoir, during the rainy and dry seasons, between the years 2016 and 2017. There was permanent occurrence of Raphidiopsis raciborskii (Woloszynska) Aguilera, Berrendero Gómez, Kastovsky, Echenique & Salerno (Phycologia 57(2):130–146, 2018), ranging between dominant and abundant, with an average biomass of 38.8 ± 29.9 mg L−1. Also abundant were Dolichospermum solitarium, D. planctonicum, Planktothrix isothrix, and Aphanizomenon gracile. Saxitoxin (STX) was detected in all the collected samples (0.11 ± 0.05 µg L−1). Microcystin (MC) was also detected, but at lower concentrations (0.01 ± 0.0 µg L−1). Low availability of NO3− and phosphorus limitation had significant effects on the R. raciborskii biomass and the levels of STX and MC. It was observed that R. raciborskii was sensitive to thermal stratification, at the same time that STX levels were higher. This suggested that STX was produced under conditions that restricted the growth of R. raciborskii. These are important findings, because they add information about the permanent occurrence of STX and R. raciborskii in an aquatic ecosystem limited by phosphorus, vulnerable to climatic variations, and polluted by domestic effluents. ICT University of São Paulo State (UNESP), Sorocaba Campus Laboratory of Toxin and Algae Natural Products University of Sao Paulo Lake Research Department UFZ-Helmholtz Centre for Environmental Research, Brueckstr 3a Department of Ecology University of São Paulo ICT University of São Paulo State (UNESP), Sorocaba Campus FAPESP: 16 / 15397-1 FAPESP: 2016 / 17266-1 CAPES: 400305/2016 CAPES: 88887.122769 / 2016-00 CAPES: 88887.141964 / 2017-00 CAPES: 99999.008107 / 2015-07

Potentially toxic Cylindrospermopsis raciborskii blooms are of emerging concerns, as its scale is spreading from tropical regions to high latitudes, increasing the risk of aquatic biota being exposed to cylindrospermopsin (CYN). So far, CYN-producing C. raciborskii strains have only been reported in tropical waters which are commonly phosphorus (P)-deficient, where they can dominate phytoplankton communities. However, the influence of CYN on phytoplankton communities under different P status remains unclear. In this study, we first analyzed the summer observations of 120 tropical reservoirs in Guangdong Province. The proportion of potential CYN-producers was significantly higher in P-deficient and CYN-present reservoirs than that in P-sufficient or CYN-absent ones. This suggested that in P-deficient condition, the potential CYN producers might gain more advantages by the help of CYN. Then, in laboratory experiments we found that upon P deprivation, CYN did not inhibit the cell growth of other algal cells, but significantly stimulates them to secret more alkaline phosphatase (ALP) than in P-sufficient condition. Through transcriptomics, we further revealed that under such P-deficient condition, CYN remarkably induced intracellular nitrogen allocation and protein export system by activating the PIK3/Akt-cGMP/PKG signaling pathways in Scenedesmus bijugatus, thus enhancing its ALP secretion. Our study implies that CYN-induced ALP secretion is facilitated upon P deficiency, thus supporting the dominance of its producers C. raciborskii.

Water bloom-forming cyanobacteria have a severe impact on freshwater quality. Although some cyanobacterial toxins such as microcystins have been studied extensively, other toxins like anatoxin-a (ATX) and their structural analogs - as well as cyanobacterial taxa producing these toxins remain to be explored in detail. The present study investigated levels of ATX, CYN and their homologs along with the occurrence of anaC and cyrJ genes in water blooms in 16 sites in the Czech Republic that were pre-selected concerning the presence of potential toxin producers. Besides, we also studied toxins and genes in a series of strains available in our laboratories. ATX and its congener HATX were detected in 5 natural biomass samples from the Czech Republic (maximum concentration 2.8 micrograms per gram d.w.). Interestingly, the anaC gene coding for ATX production was not detected in any of these toxin-positive biomass samples. The concentrations of ATX congeners in cyanobacterial laboratory strains were about 10-times higher than those of the original ATX, which calls for further research addressing levels and hazards of ATX analogs. Regarding the CYN and 7-deoxyCYN (other CYN congeners were not analyzed in this study) - these toxins were identified in a single small pond in the Czech Republic at concentrations 4.3 and 2.7 micrograms per gram of biomass d.w., respectively (corresponded to dissolved concentrations higher than 1 microgram per liter). The CYN-positive sample was dominated by CYN-producing taxa Raphidiopsis (basionym Cylindrospermopsis) and Cuspidothrix. We also confirmed the presence of a specific cyrJ gene in this natural bloom sample. To our knowledge, this is the first study pointing to Raphidiopsis (Cylindrospermopsis) and Cuspidothrix as producers of CYN in Europe. This observation calls for further research because of their increasing occurrence in (Central) Europe along with the global change. The present study demonstrates the importance of using combined (taxonomical, analytical, and molecular) approaches in the assessment of hazardous cyanobacteria and their toxins in freshwaters.

Lake Cajititlán is a small, shallow, subtropical lake located in an endorheic basin in western Mexico. It is characterized by a strong seasonality of climate with pronounced wet and dry seasons and has been classified as a hypereutrophic lake. This eutrophication was driven by improperly treated sewage discharges from four municipal wastewater treatment plants (WWTPs) and by excessive agricultural activities, including the overuse of fertilizers that reach the lake through surface runoff during the rainy season. This nutrient rich runoff has caused algal blooms, which have led to anoxic or hypoxic conditions, resulting in large-scale fish deaths that have occurred during or immediately after the rainy season. This study investigated the changes in the phytoplankton community in Lake Cajititlán during the rainy season and the association between these changes and the physicochemical water quality and environmental parameters measured in the lake’s basin.PlanktothrixandCylindrospermopsiswere the dominant genera of the cyanobacterial community, while the Chlorophyceae, Chrysophyceae, and Trebouxiophyceae classes dominated the microalgae community. However, the results showed a significant temporal shift in the phytoplankton communities in Lake Cajititlán induced by the rainy season. The findings of this study suggest that significant climatic variations cause high seasonal surface runoff and rapid changes in the water quality (Chlorophyll-a, DO, NH4+, and NO3–) and in variations in the composition of the phytoplankton community. Finally, an alternation between phosphorus and nitrogen limitation was observed in Lake Cajititlán during the rainy season, clearly correlating to the presence ofPlanktothrixwhen the lake was limited by phosphorus and to the presence ofCylindrospermopsiswhen the lake was limited by nitrogen. The evidence presented in this study supports the idea that the death of fish in Lake Cajititlán could be mainly caused by anoxia, caused by rapid changes in water quality during the rainy season. Based on our review of the literature, this is the first study on the phytoplankton community in a subtropical lake during the rainy season using high throughput 16S rRNA and 18S rRNA amplicon sequencing.

To verify whether cyanobacteria can travel from eutrophic lakes into the surrounding groundwater, a large-scale field investigation, laboratorial incubations, and quartz column penetration tests were carried out in Lake Taihu (China). High-throughput sequencing of 16S rRNA gene amplicons indicated that cyanobacteria operational taxonomic units (OTUs) were present at fifteen out of forty total wells in four cardinal directions at varying distances from the shore of Lake Taihu, up to a maximum of forty-three kilometers. Six cyanobacteria genera were detected including Microcystis, Dolichospermum, Phormidium, Leptolyngbya, Pseudanabaena and Synechococcus. The proportions of Phormidium, Microcystis and Synechococcus OTUs in the total cyanobacterial community were 45.2%, 32.2% and 19.4%, respectively. The qRT-PCR results showed that cyanobacterial abundance decreased with increasing distance from the shore of Lake Taihu. Based on the microscopic analysis of cultures inoculated with groundwater, we found Microcystis, Dolichospermum and Phormidium. Five cyanobacterial genera were able to penetrate columns filled with quartz particles ranging from 100∼200 μm. Finer layers of quartz sands were found to be impenetrable. The rating of infiltration capabilities was Microcystis > Synechococcus > Nostoc > Phormidium > Cylindrospermopsis. Deficient concentrations of microcystins were found (< 1 µg L-1) in the groundwater samples. Based on the consideration of different factors (cyanobacterial composition in Lake Taihu, peripheral groundwater, and algal soil crusts), it was deduced that Microcystis likely originated from the lake. Still, Phormidium was probably originated from the soil infiltration. These results suggest that cyanobacteria and their toxins could travel in the groundwater, but this is a size-dependent mechanism.

Changes in water level and flushing rate directly affect to a large extent the biomass of harmful cyanobacteria, and drive the shift of phytoplankton composition between cyanobacteria dominance/non-dominance in eutrophic waters. Here, we gave a theoretical formula describing the combinational effect of water level and flushing rate on cyanobacterial biomass in eutrophic and well-mixed waters. We also formulated an equation predicting the water level and flushing rate at which cyanobacteria become non-dominating in such water columns. The formulae were confronted with field observations of a low-light adapted cyanobacterium in a large coastal reservoir of southern China. Our formulae demonstrate that water level and flushing rate have an interactive effect on the equilibrium biomass of low-light adapted cyanobacteria in mixed and turbid waters. The formulae were well fitted to the field observation of Raphidiopsis raciborskii population in the reservoir during four dry seasons. In agreement with the theoretical analysis, multiple regression analysis also showed that the interaction between water level and flushing rate is able to interpret the variation of R. raciborskii biomass in the water column. The two formulae are applicable for predicting the response of low-light adapted cyanobacteria to local climate change. Our findings have practical significance in designing measures against the dominance of low light-adapted cyanobacteria in reservoirs.

The supply of drinking water is a vital challenge for the people who live on the African continent, as this continent is experiencing strong demographic growth and therefore increasing water demands. To meet these needs, surface water resources are becoming increasingly mobilized because underground resources are not always available or have already been overexploited. This situation is the case in the region of Abidjan in the Ivory Coast, where the drinking water deficit is a growing problem and it is therefore necessary to mobilize new water resources to ensure the supply of drinking water. Among the potential resources, local managers have identified a freshwater lagoon, Lagoon Aghien, That is in close proximity to the city of Abidjan. With the aim of enhancing knowledge on the ecological functioning of the lagoon and contributing to the assessment of its ability to provide drinking water, several physical and chemical parameters of the water and the phytoplankton community of the lagoon were monitored for 17 months (December 2016-April 2018) at six sampling stations. Our findings show that the lagoon is eutrophic, as evidenced by the high concentrations of total phosphorus (>140 μg L-1), nitrogen (1.36 mg L-1) and average chlorophyll-a (26 to 167 μg L-1) concentrations. The phytoplankton community in the lagoon is dominated by genera typical of eutrophic environments including mixotrophic genera such as Peridinium and by cyanobacteria such as Cylindrospermopsis/Raphidiopsis, Microcystis and Dolichospermum that can potentially produce cyanotoxins. The two rainfall peaks that occur in June and October appeared to be major events in terms of nutrient flows entering the lagoon, and the dynamics of these flows are complex. Significant differences were also found in the nutrient concentrations and to a lesser extent in the phytoplankton communities among the different stations, especially during the rainfall peaks. Overall, these results reveal that the quality of the lagoon’s water is already severely degraded, and this degradation could increase in future years due to increasing urbanization in the watershed. These results therefore raise questions about the potential use of the lagoon as a source of drinking water if measures are not taken very quickly to protect this lagoon from increasing eutrophication and other pollution sources.

High temperature can promote cyanobacterial blooms, whereas ultraviolet radiation (UVR) can potentially depress cyanobacterial growth by damaging their photosynthetic apparatus. Although the damaging effect of UVR has been well documented, reports on the interactive effects of UV radiation exposure and warming on cyanobacteria remain scarce. To better understand the combined effects of temperature and UVR on cyanobacteria, two strains of nuisance species, Microcystis aeruginosa (MIRF) and Raphidiopsis raciborskii (formerly Cylindrospermopsis raciborskii, CYRF), were grown at 24°C and 28°C and were daily exposed to UVA + UVB (PAR + UVA+UVB) or only UVA (PAR + UVA) radiation. MIRF and CYRF growth rates were most affected by PAR + UVA+UVB treatment and to a lesser extent by the PAR + UVA treatment. Negative UVR effects on growth, Photosystem II (PSII) efficiency and photosynthesis were pronounced at 24°C when compared to that at 28°C. Our results showed a cumulative negative effect on PSII efficiency in MIRF, but not in CYRF. Hence, although higher temperature ameliorates UVR damage, interspecific differences may lead to deviating impacts on different species, and combined elevated temperature and UVR stress could influence species competition.

Raphidiopsis raciborskii is an invasive bloom-forming cyanobacteria with the flexibility to utilise atmospheric and fixed nitrogen. Since nitrogen-fixation has a high requirement for iron as an ezyme cofactor, we hypothesize that iron availability would determine the success of the species under nitrogen-fixing conditions. This study compares the proteomic response of cylindrospermopsin-producing and non-toxic strains of R. racibroskii to reduced iron concentrations, under nitrogen-fixing conditions, to examine any strain-specific adaptations that might increase fitness under these conditions.. We also compared their proteomic responses at exponential and stationary growth phases to capture the changes throughout the growth cycle. Overall, the toxic strain was more competitive under Fe-starved conditions during exponential phase, with up-regulated growth and transport-related proteins. The non-toxic strain showed reduced protein expression across multiple primary metabolism pathways. We propose that the increased expression of porin proteins during the exponential growth phase enables toxic strains to persist under Fe-starved conditions with this ability providing a potential explanation for the increased fitness of cylindrospermoipsin-producing strains during unfavourable environmental conditions. This article is protected by copyright. All rights reserved.

The extent and frequency of harmful cyanobacterial blooms are increasing, owing to the climate change caused by global warming, and some harmful filamentous cyanobacteria that were first reported in the tropics are spreading to temperate regions, such as North America, Europe, and Northeast Asia. Although these exotic invasive cyanobacteria have a high toxigenic potential, they are not targeted in management plans in many countries. This study analyzed the occurrence of and potential toxin and off-flavor secondary metabolite production by invasive nostocalean cyanobacteria in the Nakdong River in Korea, which is a temperate region. The occurrence of four species belonging to three genera of cyanobacteria was confirmed in the Nakdong River. The quantities of cyanobacteria in the Nakdong River were mostly low, fewer than 1,000 cells mL-1. Twenty-four strains belonging to four species in three genera of cyanobacteria were isolated from the Nakdong River. Analysis revealed no off-flavor secondary metabolite production by any of the isolates, and those belonging to Cylindrospermopsis raciborskii, Sphaerospermopsis aphanizomenoides, and S. reniformis were identified as nontoxic strains. However, anatoxin-a production was observed in two of the eleven isolates of Cuspidothrix issatschenkoi. Given the sites and the timing of its occurrence, C. issatschenkoi had the highest potential for toxin production among the invasive nostocalean cyanobacteria appearing in the Nakdong River.

Cyanobacteria are well recognised as producers of a wide range of natural compounds that are in turn recognised as toxins that have potential and useful applications in the future as pharmaceutical agents. The order Nostocales, which is largely overlooked in this regard, has become increasingly recognised as a source of toxin producers including Anabaena, Nostoc, Hapalosiphon, Fischerella, Anabaenopsis, Aphanizomenon, Gloeotrichia, Cylindrospermopsis, Scytonema, Raphidiopsis, Cuspidothrix, Nodularia, Stigonema, Calothrix, Cylindrospermum and Desmonostoc species. The toxin compounds (i.e., microcystins, nodularin, anatoxins, ambiguines, fischerindoles and welwitindolinones) and metabolites are about to have a destructive effect on both inland and aquatic environment aspects. The present review gives an overview of the various toxins that are extracted by the order Nostocales. The current research suggests that these compounds that are produced by cyanobacterial species have promising future considerations as potentially harmful algae and as promising leads for drug discovery.

R. raciborskii is known for growing under wide ranges of temperature and light. In temperate regions, however, low temperature and high light may serve as a stressful condition for invading tropical populations. The genetic basis of R. raciborskii&rsquo, s adaptation to this combination of stresses are unknown. In this study, the growth rate and the expression of genes that may be crucial in the response to the chill/light stress of two R. raciborskii strains (differing in their climatic origin and toxicity) exposed to low temperature and high light were examined. Results showed that AMU-DH-30, a non CYN (cylindrospermopsin) producing strain isolated from the temperate region, exhibited under stress the upregulation of genes involved in the protein translation (rbp1, nusG, hflX), membrane fluidity (desA), photosynthetic activity (ccr2 and ftsH), and the accumulation of compatible solutes (asd). In contrast, a CYN producing Australian strain CS-505 was not able to adapt quickly and to continue growth during stress conditions. Intriguingly, CS-505 and AMU-DH-30 had a similar ability to resume growth when the stress conditions subsided. Moreover, in strain CS-505 the cyrB gene was significantly upregulated under the stress conditions. The presented results shed new light on the possible mechanisms involved in the response of R.raciborskii to chill/light stress.

Nitrogen and phosphorous are important nutritional regulators for the growth of cyanobacteria, thereby having a significant impact in bloom formation by toxic species. Usage of toxic cyanobacteria for increasing valuable metabolite production by nutrient manipulation is still unexplored. Hence, the current work is aimed to estimate and compare growth, pigment, and increased lipid production coupled with the identification of fatty acids between two toxic strains-Anabaena circinalis FSS 124 and Cylindrospermopsis raciborskii FSS 127 under various combinations of these two nutrients. Low level of nitrogen and phosphorous enhanced lipid content in both strains (˃ 20% and 30% respectively) and C. raciborskii, respectively. Lipid productivity in low phosphorous concentration (P0.5) was achieved significantly high in C. raciborskii. Similarly, a substantial amount of carotenoids was obtained at reduced nitrogen and phosphorous in C. raciborskii accompanied by lessened growth and Chl a concentration. Unlikely, enough biomass (˃ 2 g L-1) was produced at high nutrient levels in both species. Comparative statistical significance (p < 0.05) was found between two species regarding biomass production, chlorophyll concentration, lipid content, and productivity and between these factors in each species under both nutrient variations. FAME of Cylindrospermopsis is composed of saturated fatty acids (˃ 50%) and MUFA (˃ 25%) while Anabaena contains PUFA (˃ 21%) additionally. However, the study highlights C. raciborskii as potential lipid and carotenoid producer at nutrient stress and finds a novel way to utilize these cyanobacterial biomasses, which cause immense environmental hazards and life threats.

Hydrogen peroxide (H2O2) has been proposed as an agent to mitigate toxic cyanobacterial blooms due to the heightened sensitivity of cyanobacteria to reactive oxygen species relative to eukaryotic organisms. Here, experiments were conducted using water from four diverse, eutrophic lake ecosystems to study the effects of H2O2 on cyanobacteria and non-target members of the microbial community. H2O2 was administered at 4 &micro, g L&minus, 1 and a combination of fluorometry, microscopy, flow cytometry, and high throughput DNA sequencing were used to quantify the effects on eukaryotic and prokaryotic plankton communities. The addition of H2O2 resulted in a significant reduction in cyanobacteria levels in nearly all experiments (10 of 11), reducing their relative abundance from, on average, 85% to 29% of the total phytoplankton community with Planktothrix being highly sensitive, Microcystis being moderately sensitive, and Cylindrospermopsis being most resistant. Concurrently, eukaryotic algal levels increased in 75% of experiments. The bacterial phyla Actinobacteria, cyanobacteria, Planctomycetes, and Verrucomicrobia were most negatively impacted by H2O2, with Actinobacteria being the most sensitive. The ability of H2O2 to reduce, but not fully eliminate, cyanobacteria from the eutrophic water bodies studied here suggests it may not be an ideal mitigation approach in high biomass ecosystems.

Several cyanobacteria, including diazotrophic Raphidiopsis raciborskii, can form harmful blooms when dissolved inorganic phosphorus concentrations are very low. We hypothesized that R. raciborskii strains would vary in phosphorus (P) allocations to cell growth and storage, providing resilience of populations to continuously low or variable P supplies. We tested this hypothesis using six toxic strains (producing cylindrospermopsins) isolated from a field population using batch monocultures with and without P and dissolved inorganic nitrogen (DIN). Treatments replete with DIN, irrespective of P addition, had similar exponential growth rates for individual strains. P storage capacity varied 4-fold among strains and was significantly higher in DIN-free treatments than in replete treatments. P was stored by all R. raciborskii strains, in preference to allocation to increase growth rates. P stores decreased with increased growth rate across strains, but weeere not related to the time to P starvation in P-free treatments. The storage capacity of R. raciborskii, combined with strategies to efficiently uptake P, means that P controls may not control R. raciborskii populations in the short term. Intra-population strain variation in P storage capacity will need to be reflected in process-based models to predict blooms of R. raciborskii and other cyanobacteria adapted to low-P conditions.

Many cyanobacterial species co-occur commonly in a freshwater ecosystem and can be consumed simultaneously by zooplankton. Both Microcystis aeruginosa and Cylindrospermopsis raciborskii are the dominant species and coexist in eutrophic tropical waters, and they together are assumed to have exert a stronger effect on the life history traits of cladocerans than a single cyanobacterial species. In the present study, we tested the hypothesis with life-history experiments of Daphnia sienesis, a large cladoceran species in tropics. In the experiments, M. aeruginosa and C. raciborskii were used as a mixture of food with Chlorella pyrenoidosa for the experimental animals. D. sienesis showed excellent growth and survival on sole diets of C. pyrenoidosa (CP). By contrast, Daphnia’s growth decreased significantly and reproduction was completely inhibited when cyanobacteria comprised 100% of the food offered. The supplementation of C. pyrenoidosa into cyanobacterial diets significantly decreased their harmful effects on Daphnia, who improved the life history traits with the reduction of cyanobacterial percentage in mixed foods, irrespective of cyanobacterial species. Compared with the cultures of D. sienesis fed with a single cyanobacteria species, the animals in the treatments fed both M.aeruginosa-FACHB469 (F469) and C. raciborskii N8 (N8) had a lower growth rate in all the proportion of C. pyrenoidosa (25% CP, 50% CP or 75% CP). The strongest synergistic inhibition by the two cyanobacterial strains was found in the treatments with the 25% CP (i.e., 25% CP + 37.5% F469 + 37.5% N8), and no animal survived to maturity and reproduced. Thus, the simultaneous exposure to the two cyanobacterial species should be taken into account in assessing the ecological risks of cyanobacterial blooms, since multiple cyanobacterial coexistence can result in strong synergistic inhibition on growth and reproduction of zooplankton.

Algal cells and algal organic matter (AOM) are a source of high dissolved organic carbon (DOC) and nitrogen (DON) concentrations. This poses a possible health risk due to their potential to form disinfection by-products (DBPs), some of which may be of health concern, after disinfection. While several studies have focussed on the formation of carbonaceous DBPs from AOM, only a few studies have focussed on the formation of nitrogen containing N-DBPs from AOM. Hence, the main aim of this study was to thoroughly investigate the N-DBP formation potential of the AOM from a species of cyanobacteria commonly found in natural waters, Microcystis aeruginosa. Three haloacetonitriles, two halonitromethanes, two haloacetamides, and eight N-nitrosamines were analysed by gas chromatography-mass spectrometry after chlorination and chloramination of the extracted AOM. To provide further insight into the influence of changing DON character on N-DBP formation potential, the AOM from three other species, Chlorella vulgaris, Dolichospermum circinale and Cylindrospermopsis raciborskii, were also tested. Dichloroacetonitrile (DCAN) was the DBP formed in the highest concentrations for both chlorination and chloramination of bulk AOM from all the species. Furthermore, during chlorination and chloramination, the high molecular weight fraction (1 kDa) of AOM from M. aeruginosa had a greater DCAN formation potential (normalised to DOC or DON) than the AOM in the low molecular weight fraction (1 kDa) of M. aeruginosa, regardless of growth stage. N-Nitrosamine formation from the bulk AOM of all species occurred only after chloramination. The molar concentration of N-nitrosodimethylamine (NDMA) was lower than the other N-nitrosamines detected. However, NDMA formation increased with culture age for all four species, in contrast to most other N-nitrosamines whose formation remained consistent or decreased with culture age. Overall, algal growth could result in elevated concentrations of N-DBPs due to the increasing concentrations of high molecular weight algal DON in the AOM. It is suggested that the AOM comprises precursors containing long C-chain amine (R

In recent years, Cylindrospermopsis raciborskii blooms have been widely found worldwide. Topics dealing with the mitigation of C. raciborskii bloom is of great importance for toxins produced could threaten public health. The paper first investigated C. raciborskii dynamics over three years following sediment dredging in a shallow eutrophic Lake Dongqian (China). Based on rpoC1 gene copies, C. raciborskii bloom formed with average density of 1.30 × 106 cells/L on July 2009. One year later after sediment dredging, C. raciborskii cell density decreased below 1.17 × 105 cells/L or under detected limits during summer days on 2010. While two years later, the C. raciborskii bloom period was returned with markedly increased cell density reaching up to 4.15 × 107 cells/L on October 2011, and the maximum peak density was shown at 20.3 °C that was much lower than reported optimal growth temperature. Inferred from Spearman correlation analysis, linear regression showed C. raciborskii density was significant and positive with pH and SD, whereas they were significant and negative with TP and DO. Multiple regression analysis further demonstrated that TN, TP, SRP, pH and DO provided the best model and explained 53.1% of the variance in C. raciborskii dynamics. The approaches managing nutrients reduction might not control C. raciborskii bloom as extremely low TN (avg. 0.18 mg/L) and TP concentrations (avg. 0.05 mg/L) resulted in the highest C. raciborskii cell density after sediment dredging.

Limited information exists on the damage of harmful cyanobacteria cells, such as Raphidiopsis raciborskii and Dolichospermum circinale, caused by the hydraulic conditions at water treatment plants especially when it comes to the mechanical stresses imposed by coagulation and flocculation. To close this gap, this study evaluated the impacts of rapid and slow-mixing on R. raciborskii and D. circinale cells and trichomes. The hydraulic conditions used during the experiment were selected based on AWWA, which are widely applied in the absence of specific treatability tests. Cellular integrity was evaluated by the Erythrosine B staining method and logistic regression was used to study the association between organism integrity and hydraulic conditions (i.e., velocity gradient and mixing time). Wilcoxon rank-sum test was used to verify if there was a significant reduction of the trichome length and cell integrity. Rapid-mixing (velocity gradient of 750 s−1 for 60 s) reduced the odds of finding intact D. circinale to

Occurrence of toxic cyanobacteria and cyanotoxins in drinking, recreational, and irrigation waters represents a health hazard to wildlife and humans. This review describes the most common cyanotoxins and their producing taxa and the potential environmental health risks in marine and freshwaters of Saudi Arabia. The most common genera of toxigenic cyanobacteria detected in Saudi waters included Anabaena/Dolichospermum, Anabaenopsis, Cylindrospermopsis, Lyngbya, Microcystis, and Oscillatoria. The cyanotoxins produced by these taxa and have been detected in Saudi Arabia are microcystins (MCYSTs), cylindrospermopsin (CYN), saxitoxins, and lyngbyatoxin-like toxins. Anatoxin has not been investigated in Saudi Arabia, and extensive research is running for this toxin. Studies have detected microcystins in treated drinking waters, groundwater wells, and hot springs and their accumulation in vegetables and fish. Toxin amounts in these commodities often exceeded the WHO guidance values for safe exposure. This indicates that a human health risk could be occurring upon exposure to such potent toxins. Beyond a comprehensive analysis of cyanotoxins in marine and freshwater environments, this paper also identifies and prioritizes research gaps and suggests future research on cyanotoxins in Saudi Arabia.

The draft genome sequence of Raphidiopsis (Cylindrospermopsis) raciborskii strain GIHE 2018, a filamentous nitrogen-fixing and potentially harmful cyanobacterium, is reported here. This is the first strain isolated from a shallow freshwater pond in South Korea. This information is expected to improve our understanding of the phylogeography of this species.

Increased agricultural intensification goes with the widespread use of herbicides that adversely affect aquatic biodiversity. The effects of herbicides on toxin-producing cyanobacteria have been poorly studied. The present study aimed to investigate the toxicological and physiological effects of the herbicide clethodim on Raphidiopsis raciborskii (a.k.a. Cylindrospermopsis raciborskii) ITEPA1 and Microcystis aeruginosa BCCUSP232. On day four of the experiment, the exposure to 25 mg/L clethodim resulted in the highest cell density of R. raciborskii. Similarly, exposure to the 1, 5, 20, and 50 mg/L clethodim treatments resulted in the highest cell densities of M. aeruginosa on day 4 of the experiment. Medium effect concentrations (EC50) after 96 h of exposure of both strains to clethodim were 192.98 mg/L and 168.73 mg/L for R. raciborskii and M. aeruginosa, respectively. The presence of clethodim significantly increased the total microcystin content of M. aeruginosa compared to the control cultures. At 400 mg/L, total saxitoxins content of R. raciborskii was 27% higher than that of the control cultures on day 4. In contrast, cultures exposed to 100 mg/L clethodim had the lowest saxitoxins levels per cell quota. There was an increase in the levels of intracellular hydrogen peroxide in both species during exposure to clethodim, which was followed by significant changes (p

Meiktila Lake is a shallow reservoir located close to Meiktila city in central Myanmar. Its water is used for irrigation, domestic purposes and drinking water. No detailed study of the presence of cyanobacteria and their potential toxin production has been conducted so far. To ascertain the cyanobacterial composition and presence of cyanobacterial toxins in Meiktila Lake, water samples were collected in March and November 2017 and investigated for physico-chemical and biological parameters. Phytoplankton composition and biomass determination revealed that most of the samples were dominated by the cyanobacterium Raphidiopsis raciborskii. In a polyphasic approach, seven isolated cyanobacterial strains were classified morphologically and phylogenetically as R. raciborskii, and Microcystis spp. and tested for microcystins (MCs), cylindrospermopsins (CYNs), saxitoxins and anatoxins by enzyme-linked immunosorbent assay (ELISA) and liquid chromatography&ndash, mass spectrometry (LC&ndash, MS). ELISA and LC&ndash, MS analyses confirmed CYNs in three of the five Raphidiopsis strains between 1.8 and 9.8 &mu, g mg&minus, 1 fresh weight. Both Microcystis strains produced MCs, one strain 52 congeners and the other strain 20 congeners, including 22 previously unreported variants. Due to the presence of CYN- and MC-producing cyanobacteria, harmful effects on humans, domestic and wild animals cannot be excluded in Meiktila Lake.

As a successful invasive cyanobacterial species, Raphidiopsis raciborskii is distributed globally and shows a tendency to replace Microcystis aeruginosa in many subtropical and temperate waters, but the ecological traits that contribute to its invasiveness are still unclear. In this study, we found that R. raciborskii occurred in 149 sites in 42 lakes in eastern and central China and coexisted with M. aeruginosa at most sites. Based on field results, a combination of invasion and competition experiments using a biomass gradient to evaluate the invasiveness and competitiveness of R. raciborskii compared with M. aeruginosa was conducted. In invasive groups, both R. raciborskii and M. aeruginosa were shown to have positive specific growth rates, indicating that R. raciborskii could coexist with M. aeruginosa. Furthermore, R. raciborskii was shown to grow faster from invasion while M. aeruginosa reduced growth for invasion. In competitive groups, R. raciborskii reached a higher maximum biomass and grew longer than M. aeruginosa. The specific growth rate of R. raciborskii was not inhibited by M. aeruginosa biomass, whereas the growth of M. aeruginosa was inhibited by R. raciborskii biomass. It was shown during the whole experiment that R. raciborskii tended to replace M. aeruginosa to become dominant owing to its faster growth rate and the eventual decline in growth of M. aeruginosa. With an increase in biomass of M. aeruginosa, the vegetative cell size and filament length of R. raciborskii gradually increased. This study has demonstrated that the inherent invasive traits of R. raciborskii, size differences, niche differences, and relative fitness differences between R. raciborskii and M. aeruginosa are crucial reasons for the invasive success of R. raciborskii. Our results revealed the invasiveness and domination of R. raciborskii from a new perspective.

Toxic cyanobacteria (TCB) are well-known worldwide for their adverse impacts on humans. Species compositions and seasonal variations of TCB in reservoirs depend on interactions between physical and chemical factors. This study was conducted to evaluate the water quality in the Aha Reservoir, Southwest China, focusing on cyanobacteria and cyanotoxins. Water samples were collected weekly or biweekly from May to September of 2015 and used to delineate temporal variations in density and distribution of toxic cyanobacteria and cyanotoxins in the reservoir. Toxic cyanobacteria identified consisted of Aphanizomenon flos-aquae, Pseudanabaena limnetica, Cylindrospermopsis sp., and Microcystis sp., with Aphanizomenon flos-aquae and Pseudanabaena limnetica being the most common and significant toxic genera. The total biomass of cyanobacteria was 17.0 mg/L. Identification and quantification of microcystin variants were conducted by high performance liquid chromatography (HPLC) using a system equipped with a photodiode array detector. Microcystin levels were between 0-3.0 μg/L, MC-RR was around 0-3.0 μg/L and MC-LR was approximately 0-0.9 μg/L. Overall, the results of this study indicate that the investigated reservoirs should be monitored regularly to minimize potential health risks to the human population.

The cyanobacteriaCylindrospermopsis raciborskii, is a fresh water ubiquitous species from tropical to temperate weather. It is potentially capable of producing toxins. Thus it is necessary to monitor its presence in fresh waters associated to recreational use activities and human consumption. There are official reports and one thesis reporting the presence ofC. raciborskiiin Ecuador. Nevertheless, this country does not appear in the latest distribution maps of this species in the scientific literature. In this article, we report the presence ofC. raciborskiiin Ecuador, together with the characterization of the environmental conditions of one of the habitats where this species is present: the Limoncocha lagoon, province of Sucumbíos.

The cyanobacterium Cylindrospermopsis raciborskii is of particular concern due to its ability to fix nitrogen (N), sporadic bloom, potential toxicity and apparent invasiveness. However, the toxicity associated behavior and response of toxic C. raciborskii under N fluctuations in water have been poorly investigated. The present study initiated based on the field survey in which Cylindrospermopsis species was found to have a high fitness under nitrate concentrations fluctuating from 0.02 mg L−1 to 2.90 mg L−1 in Chinese freshwater lakes. Examination on the role of short-term N fluctuations was conducted in two C. raciborskii strains which were exposed to a range of N concentrations supplied in two patterns, namely one-time pattern and ten-time pattern in which the equal amount of N was divided into ten-time accretions. The results showed the growth of both strains were not vulnerable to the transient nutrient fluctuations. The toxic strain showed considerable toxicological flexibility with the highest yield of cylindrospermopsin (CYN) obtained in the absence of N and the lowest in full medium. Generally, larger amounts of total CYN were observed at lower N levels, indicating that N deficiency promoted the intracellular accumulation and simultaneously restrained the extracellular release of CYN. Furthermore, CYN production was significantly different in two N supply patterns. The maximum quotas of intracellular and extracellular CYN in one-time pattern were respectively 2.79–3.53 and 3.94–7.20 times higher compared to the ten-time pattern. To our knowledge, our results are the first evidence of toxicity variations of C. raciborskii to the impermanent N fluctuations, shedding new light on its toxicological plasticity.

Eutrophication and enhanced external nutrient loading of lakes and seas are most clearly reflected by increased cyanobacterial blooms, which are often toxic. Freshwater cyanobacteria produce a number of bioactive secondary metabolites, some of which have allelopathic properties, significantly influencing the biological processes of other algae, thereby affecting species composition and succession of the phytoplankton. The goal of this work was to investigate the influence of bloom-forming cyanobacterial exudates on the photophysiology of the green alga Scenedesmus quadricauda by chlorophyll fluorescence analysis. We were able to prove the effect of algal cell-free filtrates on the performance of S. quadricauda and demonstrate for the first time that the freshwater picocyanobacterium Cyanobium gracile has strong negative impact on the coexisting green alga. Neither the cyanotoxin (MYC, CYN and ATX) producing, nor the non-toxic strains showed any systematic effect on the production of S. quadricauda. Various strains of the cyanobacterium Cylindrospermopsis raciborskii inhibited the performance of the green alga independently of their origin. Our results urge further studies for a better understanding of the factors affecting the release of allelopathic compounds and the mechanisms of their effects on target organisms.

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.

A wide variety of cyanobacterial species that inhabit freshwater systems are known to produce diverse toxins and off-flavor compounds during the development of environmentally harmful blooms. However, cyanobacterial community development and toxin production potential have not been well studied. In this study, we examined the taxonomic diversity and saxitoxin production potential of cyanobacteria in the water and sediments of a large river, the North Han River in South Korea, by metagenome analysis using next-generation sequencing (NGS) and molecular biological approaches, respectively. NGS revealed that the entire cyanobacterial community in the study area consisted of 39 genera and 47 species. The most abundant genera were Microcystis, Anabaena, Cyanobium, and Synechococcus, which accounted for more than 90% of the entire community. The saxitoxin production potential of the cyanobacterial community was assessed by detecting the sxtA and sxtG genes related to saxitoxin production. Eleven sxtA and 24 sxtG genes were identified through molecular cloning and sequencing. Phylogenic analysis revealed that three sxtA genes that grouped in one phylogenic branch with Scytonema sp. were distinctly separated from the sxtA genes of Anabaena, Aphanizomenon, Lyngbya, and Cylindrospermopsis. Sixteen of the detected sxtG genes were phylogenically similar to those of Anabaena circinalis (Dolichospermum circinale), Aphanizomenon gracile, and Aphanizomenon flos-aquae. Our study demonstrates the utility of the metagenomics approach for characterizing the natural community structure of cyanobacteria containing diverse and even rare species, and the evaluation of saxitoxin-producing potential in the cyanobacterial community.

Blooms of the toxic cyanobacterium, Raphidiopsis raciborskii (basionym Cylindrospermopsis raciborskii), are becoming a major environmental issue in freshwater ecosystems globally. Our precision prevention and early detection of R. raciborskii blooms rely upon the accuracy and speed of the monitoring method. A duplex digital PCR (dPCR) monitoring approach was developed and validated to detect the abundance and toxin-producing potential of R. raciborskii simultaneously in both laboratory spiked and environmental samples. Results of dPCR were strongly correlated with traditional real time quantitative PCR (qPCR) and microscopy for both laboratory and environmental samples. However, discrepancies between methods were observed when measuring R. raciborskii at low abundance (1 − 105 cells L − 1), with dPCR showing a higher precision compared to qPCR at low cell concentration. Furthermore, the dPCR assay had the highest detection rate for over two hundred environmental samples especially under low abundance conditions, followed by microscopy and qPCR. dPCR assay had the advantages of simple operation, time-saving, high sensitivity and excellent reproducibility. Therefore, dPCR would be a fast and precise monitoring method for the early warning of toxic bloom-forming cyanobacterial species and assessment of water quality risks, which can improve prediction and prevention of the impacts of harmful cyanobacterial bloom events in inland waters.

Although some studies have investigated the impact caused by chemicals used on water treatment (coagulants and oxidants) on cyanobacteria integrity, the isolated effect of shear stress during coagulation is still not fully understood. This study evaluated the impact of different velocity gradients, mixing times, and the addition of powdered activated carbon (PAC) on the integrity of Microcystis aeruginosa, Raphidiopsis raciborskii, and Dolichospermum circinale, known producers of toxin and taste and odor (T&O) compounds. No association was found between R. raciborskii cell lysis and velocity gradient, with or without PAC, demonstrating the high resilience of this taxon to shear stress. In contrast, an association was found for M. aeruginosa at the highest velocity gradient evaluated (1000 s−1) and for D. circinale above the lowest velocity gradient studied (600 s−1). After PAC addition, there was a reduction in the chances of finding M. aeruginosa intact cells above velocity gradient 800 s−1 at 45 s, while D. circinale show cell lysis in all the scenarios expect at 600 s−1 and 10 s of agitation. The additional impact of PAC on cell lysis may lead to more release of metabolites and shows the need to adjust the hydraulic conditions in the rapid mixing stage, especially when more “fragile” cyanobacteria are present. Neither cyanobacterial cell size nor morphology was shown to be relevant to shear stress sensitivity, indicating that cell wall composition might have been an important factor in controlling cell lysis.

The increasing frequency and intensity of blooms of toxin- and taste & odour-producing filamentous cyanobacteria in water sources is a growing global issue. Compared to the common spherical Microcystis genus, the removal of filamentous cyanobacteria is more difficult in drinking water treatment plants; hence, abatement and control of the occurrence and proliferation of harmful filamentous cyanobacteria within drinking water sources is important for water supply. In this study, the solid sodium percarbonate (SPC), Na2CO3·1.5H2O2, was used as an algaecide to eliminate the cyanobacteria distributed throughout the water column in the surface and bottom layer of a reservoir serving as a drinking water source. Results showed that although the oxidation capacity of SPC was higher in the surface water due to the higher light intensity than in the bottom water, 3.0 mg/L SPC can still suppress the harmful cyanobacteria in the bottom water after 36 h because the carbonate ion generated by SPC decomposition can act as an activator of H2O2 to generate many reactive oxygen species — including superoxide radicals, carbonate radical anions, and hydroxyl radicals — even in the light-limited environment. The obtained inactivation rates for the main cyanobacteria in this reservoir followed the order: Pseudanabaena limnetica > Raphidiopsis curvata > Cylindrospermopsis raciborskii. 3.0 mg/L SPC has a slight impact on microeukaryotic communities according to the 18S rRNA gene sequencing, while 6.0 mg/L SPC changed the composition of eukaryotic phytoplankton and zooplankton clearly. Eukaryotic co-occurrence networks showed that although the network of eukaryotic plankton in treated surface water was more compact and clustered, stability of microeukaryotes in the treated surface water was lower than for the treated bottom water, owing to the higher oxidation capacity of SPC in the surface water. The results above not only have important implications for full-scale control of harmful cyanobacteria in drinking water sources, especially filamentous cyanobacteria with vertical distributions, but also help to ensure the health and stability of the whole aquatic ecosystem.

Temperate and tropical shallow lakes differ in several fundamental aspects with respect to management of eutrophication. High altitude tropical shallow lakes are a special case, showing similarities with temperate and tropical lakes. We studied the ecology of the eutrophic high-altitude tropical lake Yahuarcocha in the Ecuadorian Andes and evaluated the potential of biomanipulation to control eutrophication. With a toxin-producing Cylindrospermopsis bloom, low Secchi depth and low submerged macrophyte cover, Yahuarcocha is clearly in a turbid ecosystem state. Relatively low nutrient concentrations should theoretically allow for a shift to a clear water state through biomanipulation. Top-down control of phytoplankton by zooplankton, however, is complicated by the (1) absence of predatory fish, (2) fish community dominated by small poecelid species, (3) lack of a refuge for zooplankton from fish predation within the macrophytes, and (4) persistent, grazing resistant bloom of the cyanobacterium Cylindrospermopsis. In these aspects, lake Yahuarcocha is more similar to tropical shallow lakes, probably because water temperature is high relative to the mean air temperature and because of the absence of a cold season. The fish and macrophyte communities consisted almost entirely of exotic species. The exotic fish species probably stabilized the turbid state in the lake.

An early warning scheme is proposed that runs ensembles of inferential models for predicting the cyanobacterial population dynamics and cyanotoxin concentrations in drinking water reservoirs on a diel basis driven by in situ sonde water quality data. When the 10- to 30-day-ahead predicted concentrations of cyanobacteria cells or cyanotoxins exceed pre-defined limit values, an early warning automatically activates an action plan considering in-lake control, e.g. intermittent mixing and ad hoc water treatment in water works, respectively. Case studies of the sub-tropical Lake Wivenhoe (Australia) and the Mediterranean Vaal Reservoir (South Africa) demonstrate that ensembles of inferential models developed by the hybrid evolutionary algorithm HEA are capable of up to 30 days forecasts of cyanobacteria and cyanotoxins using data collected in situ . The resulting models for Dolicospermum circinale displayed validity for up to 10 days ahead, whilst concentrations of Cylindrospermopsis raciborskii and microcystins were successfully predicted up to 30 days ahead. Implementing the proposed scheme for drinking water reservoirs enhances current water quality monitoring practices by solely utilising in situ monitoring data, in addition to cyanobacteria and cyanotoxin measurements. Access to routinely measured cyanotoxin data allows for development of models that predict explicitly cyanotoxin concentrations that avoid to inadvertently model and predict non-toxic cyanobacterial strains.