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• High altitude connected with high UV radiation may limit the production of secondary metabolites by Cyanobacteria. • Strains isolated from two microbial mats in which no secondary metabolites were detected produced them in laboratory conditions. Ever-new cyanotoxins are being discovered, with planktic Cyanobacteria being the most studied communities, although records of cyanotoxins from benthic communities are becoming increasingly common. ​​Thus, the latter also started threatening users of water for recreational or drinking purposes. However, vast areas of the globe, i.a. Central Asia, are still understudied in this respect. Our recent study of benthic Cyanobacteria in the mountains of Eastern Pamir (Tajikistan) suggested that cyanotoxin production in high mountain environments is very limited. Here we present further study of Cyanobacteria, cyanotoxins, and other biologically active compounds such as geosmin and 2-Methylisoborneol (MIB) in microbial mats and water above them. Samples were collected in Eastern Pamirs, in UV (7–11) and altitude gradient (1000–4000 m a.s.l.). In the study, we used microscopic and genetic identification of Cyanobacteria based on NGS of V3-V4 16S rRNA amplicon and toxin assays using LC-QTOF-MS. The analyses demonstrated that the studied microbial mats contained potentially toxic Cyanobacteria (Anabaena, Lyngbya, Nostoc, Oscillatoria, and Phormidium). The production of cyanotoxins and taste and odor compounds (T&O) in natural environments was restricted to altitudes up to 3000 m a.s.l. Three water samples at 1000, 2000 and 3000 m a.s.l. contained MIB and/or geosmin, while debromoaplysiatoxin was noted at 2000 m a.s.l. Additionally, two strains (Hillbrichtia pamiria gen. nov. sp. nov. and Nostoc paludosum) isolated from sites at about 4000 m, in which no cyanotoxins or T&O were identified, produced debromoaplysiatoxin and microginin in laboratory conditions. The results suggest that in a stressful environment Cyanobacteria do not produce toxins. [ABSTRACT FROM AUTHOR]

The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O2, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H2O2 are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies. [ABSTRACT FROM AUTHOR]

Phytoplankton communities serve as useful bioindicators of environmental changes in aquatic ecosystems and can be used to assess the health of freshwater systems. Their community composition responds sensitively to changes in habitat conditions. As a result, the phytoplankton dynamics of the freshwater reservoir may differ from those of the downstream river. In the present study, we conducted a comparative analysis of the phytoplankton community between a freshwater upstream reservoir (UR) and the downstream river (DR) sections of the temperate freshwater Han River (Korea), using morphological analysis. Both UR and DR exhibited similar seasonal successions of phytoplankton groups. Diatoms dominated in autumn, winter and spring, while cyanobacteria dominated during the summer. However, the composition and frequency of the dominant species varied between UR and DR. Particularly during summer, Anabaena sp. was found to be the most frequent at UR, while Microcystis sp. was the most frequently detected at DR. In addition, high abundances of the chlorophyte Eudorina elegans and the dinoflagellate Unruhdinium penardii var. robustum were found only at DR during the autumn. The dominance and species selection of the phytoplankton community were found to be correlated with water temperature and nutrient concentrations. These results may be helpful to understand the relationship and differences in phytoplankton dynamics in reservoirs and river sections of temperate freshwater and provide guidance for maintaining the health of freshwater systems. [ABSTRACT FROM AUTHOR]

Recent studies have shown that Lake Pontchartrain Estuary in Louisiana experiences frequent harmful cyanobacterial blooms (cyanoHABs). In 2019, the Bonnet Carré Spillway (BCS) that diverts Mississippi River water into the estuary opened twice in the same year for the first time in history to prevent flooding in New Orleans. Short-term water quality monitoring was conducted in shoreline areas with high public use for the presence of cyanoHABs and cyanotoxins to assess the public health risks. Field sampling methods and satellite imagery were used to determine water quality and quantify bloom intensity and toxicity across time and space. Long-term BCS opening created a fresh (salinity < 0.2) and nutrient-rich estuary that supported several cyanoHABs in warmer months during and after the second BCS closure. Cyanobacterial biomass ranged from 35 to 4972 µg PC L−1, while toxin microcystin ranged from undetected to 8.41 µg MC L−1. The highest biomass and toxin were detected on June 25 at the north shore, station LP8, Mandeville Beach, dominated by Microcystis and Dolichospermum species. CyanoHABs occurred mostly in the northern part of the estuary, where tributary discharge is also a strong influence. Some of these blooms exited the estuary and were transported to the Gulf of Mexico following passage through Lake Borgne and then Mississippi Sound. Modifications in the timing and duration of river diversion operations can create prolonged cyanobacterial blooms that can cause environmental and public health risks, especially in warmer months, and this may intensify due to a changing climate. [ABSTRACT FROM AUTHOR]

AbstractPhytoplankton communities serve as useful bioindicators of environmental changes in aquatic ecosystems and can be used to assess the health of freshwater systems. Their community composition responds sensitively to changes in habitat conditions. As a result, the phytoplankton dynamics of the freshwater reservoir may differ from those of the downstream river. In the present study, we conducted a comparative analysis of the phytoplankton community between a freshwater upstream reservoir (UR) and the downstream river (DR) sections of the temperate freshwater Han River (Korea), using morphological analysis. Both UR and DR exhibited similar seasonal successions of phytoplankton groups. Diatoms dominated in autumn, winter and spring, while cyanobacteria dominated during the summer. However, the composition and frequency of the dominant species varied between UR and DR. Particularly during summer, Anabaena sp. was found to be the most frequent at UR, while Microcystis sp. was the most frequently detected at DR. In addition, high abundances of the chlorophyte Eudorina elegans and the dinoflagellate Unruhdinium penardii var. robustum were found only at DR during the autumn. The dominance and species selection of the phytoplankton community were found to be correlated with water temperature and nutrient concentrations. These results may be helpful to understand the relationship and differences in phytoplankton dynamics in reservoirs and river sections of temperate freshwater and provide guidance for maintaining the health of freshwater systems.

This study explored the effects of H 2 O 2 on Cyanobacteria and non-target microbes using fluorometry, microscopy, flow cytometry, and high throughput DNA sequencing of the 16S rRNA gene during a series of mesocosm and whole-ecosystem experiments in a eutrophic pond in NY, USA. The addition of H 2 O 2 (8 mg/L) significantly reduced Cyanobacteria concentrations during a majority of experiments (66%; 6 of 9) and significantly increased eukaryotic green and unicellular brown algae in 78% and 45% of experiments, respectively. While heterotrophic bacteria declined significantly following H 2 O 2 addition in all experiments, bacteria indicative of potential fecal contamination (Escherichia coli, Enterococcus , fecal coliform bacteria) consistently and significantly increased in response to H 2 O 2 , evidencing a form of 'pollution swapping'. H 2 O 2 more effectively reduced Cyanobacteria in enclosed mesocosms compared to whole-ecosystem applications. Ten whole-pond H 2 O 2 applications over a two-year period temporarily reduced cyanobacterial levels but never reduced concentrations below bloom thresholds and populations always rebounded in two weeks or less. The bacterial phyla of Cyanobacteria, Actinobacteria, and Planctomycetes were the most negatively impacted by H 2 O 2. Microcystis was always reduced by H 2 O 2 , as was the toxin microcystin, but Microcystis remained dominant even after repeated H 2 O 2 treatments. Although H 2 O 2 favored the growth of eukaryotic algae over potentially harmful Cyanobacteria, the inability of H 2 O 2 to end cyanobacterial blooms in this eutrophic waterbody suggests it is a non-ideal mitigation approach in high biomass ecosystems and should be used judiciously due to potential negative impacts on non-target organisms and promotion of bacteria indicative of fecal contamination. [Display omitted] [ABSTRACT FROM AUTHOR]

Frequent outbreaks of harmful cyanobacterial blooms and the cyanotoxins they produce not only seriously jeopardize the health of freshwater ecosystems but also directly affect the survival of aquatic organisms. In this study, the dynamic characteristics and response patterns of transcriptomes and gut microbiomes in gastropod Bellamya aeruginosa were investigated to explore the underlying response mechanisms to toxic cyanobacterial exposure. The results showed that toxic cyanobacteria exposure induced overall hepatopancreatic transcriptome changes. A total of 2128 differentially expressed genes were identified at different exposure stages, which were mainly related to antioxidation, immunity, and metabolism of energy substances. In the early phase (the first 7 days of exposure), the immune system may notably be the primary means of resistance to toxin stress, and it performs apoptosis to kill damaged cells. In the later phase (the last 7 days of exposure), oxidative stress and the degradation activities of exogenous substances play a dominant role, and nutrient substance metabolism provides energy to the body throughout the process. Microbiomic analysis showed that toxic cyanobacteria increased the diversity of gut microbiota, enhanced interactions between gut microbiota, and altered microbiota function. In addition, the changes in gut microbiota were correlated with the expression levels of antioxidant-, immune-, metabolic-related differentially expressed genes. These results provide a comprehensive understanding of gastropods and intestinal microbiota response to toxic cyanobacterial stress. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms and their toxigenic potential threaten freshwater resources worldwide. In Atlantic Canada, despite an increase of cyanobacterial blooms in the last decade, little is known about the toxigenic potential and the taxonomic affiliation of bloom-forming cyanobacteria. In this study, we employed polymerase chain reaction (PCR) and metagenomic approaches to assess the potential for cyanotoxin and other bioactive metabolite production in Harvey Lake (oligotrophic) and Washademoak Lake (mesotrophic) in New Brunswick, Canada, during summer and early fall months. The PCR survey detected the potential for microcystin (hepatotoxin) and anatoxin-a (neurotoxin) production in both lakes, despite a cyanobacterial bloom only being visible in Washademoak. Genus-specific PCR associated microcystin production potential with the presence of Microcystis in both lakes. The metagenomic strategy provided insight into temporal variations in the microbial communities of both lakes. It also permitted the recovery of a near-complete Microcystis aeruginosa genome with the genetic complement to produce microcystin and other bioactive metabolites such as piricyclamide, micropeptin/cyanopeptolin, and aeruginosin. Our approaches demonstrate the potential for production of a diverse complement of bioactive compounds and establish important baseline data for future studies of understudied lakes, which are frequently affected by cyanobacterial blooms.

Toxic cyanobacterial blooms are recurrent for few decades throughout the globe, due to climate change, atmospheric warming and various anthropogenic activities with severe impacts of potential toxins on various ecosystems finally affecting the entire environment. These cyanobacteria are merely unexplored regarding their biochemical components except toxins. Variable influences and interactions of different factors including nitrogen, carbon, and availability of light are well known to crucially regulate cyanobacterial growth and metabolism. Thus, current research work is motivated for the evaluation and optimization of the effects of the aforementioned vital factors for improvement of biomass and lipid production of a freshwater, toxic strain of Anabaena circinalis. The modelling and optimization of factors such as nitrogen, light intensity and bicarbonate concentration (source of carbon) to maximize growth and lipid production were based on 20 design point experiments by Response Surface Methodology (RSM) and optimized values were further improved and validated by Particle Swarm Optimization (PSO) algorithm. The maximum optima were obtained 1.829 g L-1 and 39.64 % for biomass production and lipid content respectively from PSO optimization with two different sets of optimal values of factors. It shows 0.44 % and 2.77 % higher values of responses than that of RSM optimization. These asynchronous findings pioneered the enhanced lipid accumulation as well as the growth of a toxic cyanobacterium by optimizing interaction effects of culture conditions through various statistical and computational approaches. • Influencing factors were optimized for the improvement of biomass and lipid production. • RSM was used to optimize the system parameters and validated by PSO algorithm. • Maximum optima were obtained as 1.829 g L-1 and 39.64 % for biomass production. • Results shows that 0.44 % and 2.77 % higher values than that of RSM optimization. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the influence of agricultural by-products on the proliferation of potentially toxic microalgae in rice-fish farming. For this purpose, an experiment was carried out in rice-fish culture ponds growing Oreochromis niloticus with four dietary treatments: corn bran input (RSM), rice bran input (RSR), mixed byproduct input (RPC) and no feed input (RC). Phytotoxic Dinoflagellata and Cyanobacteria from these ponds were collected monthly for six months. Sampling of these microalgae was done by water filtration and scraping of the algal biofilm attached to the submerged parts of the rice stems. In addition, the physico-chemical parameters of the water in these ponds were measured. The analyses recorded a total of 44 phytotoxic microalgal taxa, including 33 Cyanobacteria and 11 Dinoflagellata with eight taxa constant in the ponds. The majority of these taxa are likely to produce hepatotoxins and neurotoxins in the ponds. The absolute density of potentially toxic pelagic microalgae was significantly higher in RPC (15339 to 24450 Individuals/L) than that in RC (5586 to13078 Individuals/L). Moreover, the density of potentially toxic microalgae epiphytic on submerged rice stems was higher in RPC (113.5 to 160.5 Individuals/cm2) than that in RC (85.5 to 115.96 Individuals/cm2). In contrast to other ponds. Anabaena affinis, Microcystis aeruginosa, Peridinium cinctum and Protoperidinium sp. were the most abundant. The use of rice bran and its combination with other agricultural by-products in rice-fish farming results in the proliferation of toxic Cyanobacteria that would be harmful to fish health. [ABSTRACT FROM AUTHOR]

Anthropogenic impacts are expected to increase the co-occurrence of stressors that can fundamentally alter ecosystem structure and function. To cope with stress, many organisms locally adapt, but how such adaptations affect the ability of an organism to manage co-occurring stressors is not well understood. In aquatic ecosystems, elevated temperatures and harmful algal blooms are common co-stressors. To better understand the role and potential trade-offs of local adaptations for mitigating the effects of stressors, Daphnia pulicaria genotypes that varied in their ability to consume toxic cyanobacteria prey (i.e., three tolerant and three sensitive) were exposed to five diets that included combinations of toxic cyanobacteria, Microcystis aeruginosa, and a green alga, Ankistrodesmus falcatus, under two temperatures (20 °C vs. 28 °C). A path analysis was conducted to understand how local adaptations affect energy allocation to intermediate life history traits (i.e., somatic growth, fecundity, survival) that maximize Daphnia fitness (i.e., population growth rate). Results from the 10-day study show that tolerant Daphnia genotypes had higher fitness than sensitive genotypes regardless of diet or temperature treatment, suggesting toxic cyanobacteria tolerance did not cause a decrease in fitness in the absence of cyanobacteria or under elevated temperatures. Results from the path analysis demonstrated that toxic cyanobacteria had a stronger effect on life history traits than temperature and that population growth rate was mainly constrained by reduced fecundity. These findings suggest that local adaptations to toxic cyanobacteria and elevated temperatures are synergistic, leading to higher survivorship of cyanobacteria-tolerant genotypes during summer cyanobacterial bloom events. [ABSTRACT FROM AUTHOR]

Cyanotoxins are an emerging threat to freshwater resources worldwide. The most frequently reported cyanotoxins are the microcystins, which threaten the health of humans, wildlife, and ecosystems. Determining the potential for microcystin production is hindered by a lack of morphological features that correlate with microcystin production. However, amplicon‐based methods permit the detection of microcystin biosynthesis genes and were employed to assess the toxin potential in Lake Utopia, NB, Canada, an oligotrophic lake that occasionally experiences cyanobacteria blooms. Samples collected at 2 week intervals from June 27th to September 27th, 2016, were screened by polymerase chain reaction (PCR) for the microcystin synthetase E gene (mcyE). The mcyE gene was present in some samples every sampling day, despite microcystin not being detected via ELISA, and was most frequently associated with the larger pore size fractions of the serially filtered samples. Further PCR surveys using primer sets to amplify genus‐specific (e.g., Microcystis, Anabaena/Dolichospermum, and Planktothrix) mcyE fragments identified Microcystis as the only taxa in Lake Utopia with toxigenic potential. Sequencing of the 16S rRNA V3–V4 region revealed a community dominated by members of the order Synechococcales (from 38 to 96% relative abundance), but with significant presence of taxa from Cyanobacteriales including Microcystaceae and Nostocaceae. A persistent Microcystis population was detected in samples both testing positive and negative for the mcyE gene, highlighting the importance of identifying cyanotoxin production potential by gene presence and not species identity. To our knowledge, this study represents the first application of amplicon‐based approaches to studying toxic cyanobacteria in an understudied region—Atlantic Canada. [ABSTRACT FROM AUTHOR]

Maekuang reservoir is one of the water resources which provides water supply, livestock, and recreational in Chiangmai city, Thailand. The water quality and Microcystis aeruginosa are a severe problem in many reservoirs. M. aeruginosa is the most widespread toxic cyanobacteria in Thailand. Difficulty prediction for planning protects Maekuang reservoirs, the artificial Neural Network (ANN) model is a powerful tool that can be used to machine learning and prediction by observation data. ANN is able to learn from previous data and has been used to predict the value in the future. ANN consists of three layers as input, hidden, and output layer. Water quality data is collected biweekly at Maekuang reservoir (1999-2000). Input data for training, including nutrients (ammonium, nitrate, and phosphorus), Secchi depth, BOD, temperature, conductivity, pH, and output data for testing as Chlorophyll a and M. aeruginosa cells. The model was evaluated using four performances, namely; mean squared error (MSE), root mean square error (RMSE), sum of square error (SSE), and percentage error. It was found that the model prediction agreed with experimental data. C01-C08 scenarios focused on M. aeruginosa bloom prediction, and ANN tested for prediction of Chlorophyll a bloom shown on M01-M09 scenarios. The findings showed, this model has been validated for prediction of Chlorophyll a and shows strong agreement for nitrate, Log cell, and Chlorophyll a. Results indicate that the ANN can be predicted eutrophication indicators during the summer season, and ANN has efficient for providing the new data set and predict the behavior of M. aeruginosa bloom process.

Frequent outbreaks of harmful cyanobacterial blooms and the cyanotoxins they produce not only seriously jeopardize the health of freshwater ecosystems but also directly affect the survival of aquatic organisms. In this study, the dynamic characteristics and response patterns of transcriptomes and gut microbiomes in gastropod Bellamya aeruginosa were investigated to explore the underlying response mechanisms to toxic cyanobacterial exposure. The results showed that toxic cyanobacteria exposure induced overall hepatopancreatic transcriptome changes. A total of 2128 differentially expressed genes were identified at different exposure stages, which were mainly related to antioxidation, immunity, and metabolism of energy substances. In the early phase (the first 7 days of exposure), the immune system may notably be the primary means of resistance to toxin stress, and it performs apoptosis to kill damaged cells. In the later phase (the last 7 days of exposure), oxidative stress and the degradation activities of exogenous substances play a dominant role, and nutrient substance metabolism provides energy to the body throughout the process. Microbiomic analysis showed that toxic cyanobacteria increased the diversity of gut microbiota, enhanced interactions between gut microbiota, and altered microbiota function. In addition, the changes in gut microbiota were correlated with the expression levels of antioxidant-, immune-, metabolic-related differentially expressed genes. These results provide a comprehensive understanding of gastropods and intestinal microbiota response to toxic cyanobacterial stress.

During the study into the microbial biodiversity and bioactivity of the Microcystis phycosphere, a new yellow-pigmented, non-motile, rod-shaped bacterium containing polyhydroxybutyrate granules designated as strain Z10-6T was isolated from highly-toxic Microcystis aeruginosa Kützing M.TN-2. The new isolate produces active bioflocculating exopolysaccharides. Phylogenetic analysis based on 16S rRNA gene sequences indicated strain Z10-6T belongs to the genus Sphingopyxis with highest similarity to Sphingopyxis solisilvae R366T (98.86%), and the similarity to other Sphingopyxis members was less than 98.65%. However, both low values obtained by phylogenomic calculation of average nucleotide identity (ANI, 85.5%) and digital DNA-DNA hybridization (dDDH, 29.8%) separated the new species from its closest relative. The main polar lipids were sphingoglycolipid, phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, one unidentified glycolipid and one unidentified aminophospholipid. The predominant fatty acids were summed feature 8, C17:1ω6c, summed feature 3, C16:0, C18:1ω7c 11-methyl and C14:0 2-OH. The respiratory quinone was ubiqunone-10, with spermidine as the major polyamine. The genomic DNA G + C content was 64.8 mol%. Several biosynthesis pathways encoding for potential new bacterial bioactive metabolites were found in the genome of strain Z10-6T. The polyphasic analyses clearly distinguished strain Z10-6T from its closest phylogenetic neighbors. Thus, it represents a novel species of the genus Sphingopyxis, for which the name Sphingopyxis microcysteis sp. nov. is proposed. The type strain is Z10-6T (= CCTCC AB2017276T = KCTC 62492T). [ABSTRACT FROM AUTHOR]

• MC-LR exhibits reproductive toxicity, with a greater impact on spermary. • In toxic inheritance, F1 survival rate is affected by different factors of F0. • Offspring survival was unaffected by the exposed MC-LR concentration of mother. • The surviving offspring of paternal inheritance have a higher tolerance to MC-LR. Cyanobacteria cell lysates release numerous toxic substances (e.g., cyanotoxins) into the water, posing a serious threat to human health and aquatic ecosystems. Microcystins (MCs) are among the most abundant cyanotoxins in the cell lysates, with microcystin-LR (MC-LR) being one of the most common and highly toxic congeners. In this study, zebrafish (Danio rerio) were exposed to different levels MC-LR that from extracts of Microcystis aeruginosa. Changes in the MC-LR accumulations, organ coefficients, and antioxidant enzyme activities in the zebrafish were analyzed. Transgenerational reproductive toxicity of MC-LR in the maternal and paternal generations was further investigated, as well as the influences of extracts containing MC-LR exposures of the F1 on the growth of zebrafish. The study found that high levels of MC-LR could be detected in the major organs of adult zebrafish, particularly in spleen. Notably, concentration of MC-LR in the spermary was significantly higher than that in the ovarium. MC-LR could induce oxidative damage by affecting the activities of catalase and superoxide dismutase. Inherited from F0, MC-LR led to impaired development in the F1 generation. Difference in offspring survival rates could be observed in the groups with different MC-LR levels of maternal and paternal exposures. This study reveals transgenerational effects of MC-LR on the reproductive toxicity and offspring growth inhibition to the aquatic organisms, which should be emphasized in the future ecological risk assessment. [ABSTRACT FROM AUTHOR]

Eutrophication of surface waters caused by toxic cyanobacteria such as Microcystis aeruginosa leads to the release of secondary metabolites called Microcystins (MCs), which are heptapeptides with adverse effects on soil microbiota, plants, animals, and human health. Therefore, to avoid succumbing to the negative effects of these cyanotoxins, various remediation approaches have been considered. These techniques involve expensive physico-chemical processes because of the specialized equipment and facilities required. Thus, implementing eco-technologies capable of handling this problem has become necessary. Indeed, multi-soil-layering (MSL) technology can essentially meet this requirement. This system requires little space, needs simple maintenance, and has energy-free operation and high durability (20 years). The performance of the system is such that it can remove 1.16 to 4.47 log10 units of fecal contamination from the water, 98% of suspended solids (SS), 92% of biological oxygen demand (BOD), 98% of chemical oxygen demand (COD), 92% of total nitrogen (TN), and 100% of total phosphorus (TP). The only reported use of the system to remove cyanotoxins has shown a 99% removal rate of MC-LR. However, the mechanisms involved in removing this toxin from the water are not fully understood. This paper proposes reviewing the principal methods employed in conventional water treatment and other technologies to eliminate MCs from the water. We also describe the principles of operation of MSL systems and compare the performance of this technology with others, highlighting some advantages of this technology in removing MCs. Overall, the combination of multiple processes (physico-chemical and biological) makes MSL technology a good choice of cyanobacterial contamination treatment system that is applicable in real-life conditions, especially in rural areas.

The aim of this study was to assess the efficiency of the innovative SED-BIO system in limiting the inflow of pollutants to Jelonek Lake. The analyses were conducted in the Gniezno Lake District in Greater Poland (the western part of Poland). Physical and chemical analyses were conducted in the years 2016–2019. The results demonstrate that the system is highly effective in the reduction of such nutrients as nitrogen (NO3−—63%; NH4+—14.9%) and phosphorus (PO43−—19.3%). Although the presence of cyanobacteria was confirmed practically throughout the whole monitoring period of the system (2016), the specimens found in most samples were not toxigenic genotypes with a potential to produce microcystins. Microcystins (3 µg·L−1) were detected only once, immediately after the SED-BIO system had been installed in the river and pond, which demonstrates that this natural toxin was eliminated from the additional pool of contaminants that might be transported to Jelonek Lake.

While transfer of freshwater cyanobacteria to estuaries has been observed worldwide, the associated transfer of cyanotoxins is less often reported, in particular the sediment contribution. During fall 2018, we monitored the co-occurrence of cyanobacteria and microcystin (MC) in both the water column and in surface sediments at five stations along a river continuum, from a freshwater reservoir to the coastal area in Brittany, France. Cyanobacteria dominated the phytoplankton community in the water column with high densities at the freshwater sites. Microcystis cells and intracellular MC transfer to estuarine and marine sites were observed with decreasing concentrations in accordance with flow dilution. Extracellular MC showed the opposite trend and increased from upstream to downstream in accordance with the lysing of the cells at elevated salinities. Surface sediment samples contained high densities of colonial Microcystis in freshwater and with decreasing concentrations along the salinity gradient, similar to cells concentrations in the water column. Intracellular MC was detected in sediment at all sites except at the marine outlet suggesting the survival of intact cells. Extracellular MC concentrations in sediment were up to five times higher than intracellular concentrations suggesting incomplete MC degradation. mcyB genes were present at all sites, while mcyA genes were absent at the marine outlet suggesting the presence of toxic strains along the estuary. The high densities of intact colonies of potentially toxic Microcystis in the estuarine sediment strongly suggest that sediments can act as an inoculum of cyanobacteria and cyanotoxins in estuaries. [ABSTRACT FROM AUTHOR]

Trophic status of twenty-four water reservoirs of the eastern of Cuba was evaluated, classifying these reservoirs according to the eutrophication level. The average trophic state index (TSI) was calculated considering chlorophyll a, transparency and total phosphorus. A cluster analysis with TSI values allow to establish five eutrophic levels with specific ranges and attributes, modifying the classical Carlson criteria. The most eutrophic reservoirs were Chalóns and Camazán (level 4). It was confirmed direct relationship between eutrophic and cyanobacteria bloom occurrence, being the most contaminated those with higher risk. Toxic bloom-forming species were detected in Parada, Baraguá, La Yaya, Mícara, Bio and Guisa, Chalóns and Camazán, involving cyanobacteria like Synechocystis aquatilis, Cylindrospermopsis raciborskii, Oscillatoria sp., Microcystis aeruginosa, M. flos-aquae, M. panniformis,M. wesenbergii, Planktolyngbya limnetica, and Synechococcus sp. [ABSTRACT FROM AUTHOR]

In aquatic environments, interactions between cyanobacteria and their grazers are crucial for ecosystem functioning. Cyanobacteria are photosynthetic prokaryotes, which are able to produce large blooms and associated toxins, some of which are able to suppress grazer fitness. Cyanobacterial blooms are intensified by global warming and eutrophication. In our experiments, the tolerance of Daphnia magna (Straus, 1820), an efficient grazer of toxic cyanobacteria, was studied. We used different D. magna clones sampled from different sediment depths, which corresponded to different time periods of eutrophication. Our results showed that different clones had a different tolerance towards the toxic cyanobacterial species, Microcystis aeruginosa, confirming the presence of genetic variation in D. magna tolerance to cyanobacteria. However, there was not a significant adaptive effect of sediment depth. As expected, in general under controlled, infection-free conditions M. aeruginosa reduced D. magna survival. However, a coincidental, non-intended opportunistic fungal infection in a first experiment allowed us to compare the response of D. magna to M. aeruginosa in infected individuals and non-infected individuals (from a second experiment). In the presence of this opportunistic infection, there was no negative effect of M. aeruginosa in the D. magna clones, suggesting that exposure to the infection provided protection for Daphnia individuals towards Microcystis. Biotic interactions can thus be important in the interpretation of cyanobacterial effects in zooplankton grazers and in finding appropriate solutions to reduce the occurrence of cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

Increasing toxic cyanobacterial blooms in freshwater demand environmentally friendly solutions to control their growth and toxicity, especially in arid countries, where most drinking water is produced from surface reservoirs. We tested the effects of macrophyte allelochemicals on Microcystis aeruginosa and on the fundamental role of bacteria in nutrient recycling. The effects of Ranunculus aquatilis aqueous extract, the most bioactive of four Moroccan macrophyte extracts, were tested in batch systems on M. aeruginosa growth, toxin production and oxidative stress response and on the ectoenzymatic activity associated with the bacterial community. M. aeruginosa density was reduced by 82.18%, and a significant increase in oxidative stress markers was evidenced in cyanobacterial cells. Microcystin concentration significantly decreased, and they were detected only intracellularly, an important aspect in managing toxic blooms. R. aquatilis extract had no negative effects on associated bacteria. These results confirm a promising use of macrophyte extracts, but they cannot be generalized. The use of the extract on other toxic strains, such as Planktothrix rubescens, Raphidiopsis raciborskii and Chrysosporum ovalisporum, caused a reduction in growth rate but not in cyanotoxin content, increasing toxicity. The need to assess species-specific cyanobacteria responses to verify the efficacy and safety of the extracts for human health and the environment is highlighted.

Macroalgae can directly restrict the growth of various phytoplankton species by releasing allelopathic compounds; therefore, considerable attention should be paid to the allelopathic potential of these organisms against harmful and bloom-forming cyanobacteria. The main aim of this study was to demonstrate for the first time the allelopathic activity of Ulva intestinalis on the growth, the fluorescence parameters: the maximum PSII quantum efficiency (Fv/Fm) and the effective quantum yield of PSII photochemistry (ΦPSII), the chlorophyll a (Chl a) and carotenoid (Car) content, and the microcystin-LR (MC-LR) and phenol content of three bloom-forming cyanobacteria, Aphanizomenon sp., Nodularia spumigena, and Nostoc sp. We found both negative and positive allelopathic effects of U. intestinalis on tested cyanobacteria. The study clearly showed that the addition of the filtrate of U. intestinalis significantly inhibited growth, decreased pigment content and Fv/Fm and ΦPSII values of N. spumigena and Nostoc sp., and stimulated Aphanizomenon sp. The addition of different concentrations of aqueous extract also stimulated the cyanobacterial growth. It was also shown that the addition of extract obtained from U. intestinalis caused a significant decrease in the MC-LR content in Nostoc sp. cells. Moreover, it the phenol content in N. spumigena cells was increased. On the other hand, the cell-specific phenol content for Aphanizomenon sp. decreased due to the addition of the filtrate. In this work, we demonstrated that the allelopathic effect of U. intestinalis depends on the target species’ identity as well as the type of allelopathic method used. The study of the allelopathic Baltic macroalgae may help to identify their possible role as a significant biological factor influencing harmful cyanobacterial blooms in brackish ecosystems.

Blooms of cyanobacteria are frequent in Brazilian water reservoirs used for drinking water. The warning for the presence of potential toxin-producing cyanobacteria is typically based on time-consuming microscopy, rather than specific molecular detection of toxic genes in cyanobacteria. In this study, we developed a quantitative PCR assay for the detection of cyanobacteria producing the neurotoxin saxitoxin (STX). The assay targets the sxtA gene in the sxt gene cluster. Potential and dominant STX-producers in the Itupararanga reservoir were the genera Raphidiopsis, Aphanizomenon and Geitlerinema. Numbers of the sxtA gene varied from 6.76 × 103 to 7.33 × 105 cells mL−1 and correlated positively with SXT concentrations in the water. Concentrations of STX and the sxtA gene also correlated positively with TN:TP ratio and pH, but correlated negatively with inorganic nutrients and turbidity, confirming that regulation of the SXT production was impacted by environmental variables. In contrast, the occurrence of another cyanotoxin, microcystin, did not correlate with any environmental variables. The developed qPCR assay was found to be a rapid and robust approach for the specific quantification of potential STX-producing cyanobacteria and should be considered in future investigations on toxic cyanobacteria to provide an early warning of potential toxin episodes.

• Combined effects of toxic Microcystis aeruginosa and hypoxia on the digestive enzyme activities are investigated in mussels. • Toxic M. aeruginosa significantly increases the digestive enzyme activities, whereas enzyme activities are reduced by hypoxia. • Hypoxia and toxic M. aeruginosa have conflicting effects on the digestive enzyme activities. Nowadays, eutrophication is a very popular environmental problem in numerous waters around the world. The main reason of eutrophication is the enrichment of the nutrient, which results in the excessive growth of phytoplankton and some of them are toxic and harmful. Fortunately, some studies have shown that some bivalves can filter the overgrown phytoplankton in water, which may alleviate water eutrophication. However, the physiological effects of toxic cyanobacteria on filter feeding animal have not been clarified very well. In this experiment, digestive enzyme activities in Hyriopsis cumingii exposed to different concentrations of the toxic Microcystis aeruginosa (0, 5 * 105 and 5 *106 cell ml-1) at two dissolved oxygen (DO) levels (6 and 2 mg l-1) for 14 days were investigated. Toxic M. aeruginosa significantly affected all digestive enzyme activities throughout the experiment. At high toxic M. aeruginosa concentration, the activities of cellulase, amylase and lipase in digestive gland and stomach were significantly increased (P<0.05). However, hypoxia reduced the activities of cellulase, amylase and lipase in digestive gland and stomach. Conflicting effects were observed between toxic M. aeruginosa and DO in most digestive enzyme activities during the exposure period. Therefore, it is not conducive for the digestion and absorption of M. aeruginosa in H. cumingii under hypoxic conditions. H. cumingii is tolerant to toxic M. aeruginosa and may remove toxic cyanobacteria from waters under normal DO conditions. [ABSTRACT FROM AUTHOR]

Humans have artificially enhanced the productivity of terrestrial and aquatic ecosystems on a global scale by increasing nutrient loading. While the consequences of eutrophication are well known (e.g., harmful algal blooms and toxic cyanobacteria), most studies tend to examine short-term responses relative to the time scales of heritable adaptive change. Thus, the potential role of adaptation by organisms in stabilizing the response of ecological systems to such perturbations is largely unknown. We tested the hypothesis that adaptation by a generalist consumer (Daphnia pulicaria) to toxic prey (cyanobacteria) mediates the response of plankton communities to nutrient enrichment. Overall, the strength of Daphnia's top–down effect on primary producer biomass increased with productivity. However, these effects were contingent on prey traits (e.g., rare vs. common toxic cyanobacteria) and consumer genotype (i.e., tolerant vs sensitive to toxic cyanobacteria). Tolerant Daphnia strongly suppressed toxic cyanobacteria in nutrient-rich ponds, but sensitive Daphnia did not. In contrast, both tolerant and sensitive Daphnia genotypes had comparable effects on producer biomass when toxic cyanobacteria were absent. Our results demonstrate that organismal adaptation is critical for understanding and predicting ecosystem-level consequences of anthropogenic environmental perturbations. [ABSTRACT FROM AUTHOR]

The evaluation of effluent wastewater quality mainly relies on the assessment of conventional bacterial indicators, such as fecal coliforms and enterococci; however, little is known about opportunistic pathogens, which can resist chlorination and may be transmitted in aquatic environments. In contrast to conventional microbiological methods, high-throughput molecular techniques can provide an accurate evaluation of effluent quality, although a limited number of studies have been performed in this direction. In this work, high-throughput amplicon sequencing was employed to assess the effectiveness of chlorination as a disinfection method for secondary effluents. Common inhabitants of the intestinal tract, such as Bacteroides, Arcobacter and Clostridium, and activated sludge denitrifiers capable of forming biofilms, such as Acidovorax, Pseudomonas and Thauera, were identified in the chlorinated effluent. Chloroflexi with dechlorination capability and the bacteria involved in enhanced biological phosphorus removal, i.e., Candidatus Accumulibacter and Candidatus Competibacter, were also found to resist chlorination. No detection of Escherichia indicates the lack of fecal coliform contamination. Mycobacterium spp. were absent in the chlorinated effluent, whereas toxin-producing cyanobacteria of the genera Anabaena and Microcystis were identified in low abundances. Chlorination significantly affected the filamentous bacteria Nocardioides and Gordonia, whereas Zoogloea proliferated in the disinfected effluent. Moreover, perchlorate/chlorate- and organochlorine-reducing bacteria resisted chlorination.

Aquatic toxins are potent natural toxins produced by certain cyanobacteria and marine algae species during harmful cyanobacterial and algal blooms (CyanoHABs and HABs, respectively). These harmful bloom events and the toxins produced during these events are a human and environmental health concern worldwide, with occurrence, frequency and severity of CyanoHABs and HABs being predicted to keep increasing due to ongoing climate change scenarios. These contexts, as well as human health consequences of some toxins produced during bloom events have been thoroughly reviewed before. Conversely, the wider picture that includes the non-human biota in the assessment of noxious effects of toxins is much less covered in the literature and barely covered by review works. Despite direct human exposure to aquatic toxins and related deleterious effects being responsible for the majority of the public attention to the blooms' problematic, it constitutes a very limited fraction of the real environmental risk posed by these toxins. The disruption of ecological and trophic interactions caused by these toxins in the aquatic biota building on deleterious effects they may induce in different species is paramount as a modulator of the overall magnitude of the environmental risk potentially involved, thus necessarily constraining the quality and efficiency of the management strategies that should be placed. In this way, this review aims at updating and consolidating current knowledge regarding the adverse effects of aquatic toxins, attempting to going beyond their main toxicity pathways in human and related models' health, i.e., also focusing on ecologically relevant model organisms. For conciseness and considering the severity in terms of documented human health risks as a reference, we restricted the detailed revision work to neurotoxic cyanotoxins and marine toxins. This comprehensive revision of the systemic effects of aquatic neurotoxins provides a broad overview of the exposure and the hazard that these compounds pose to human and environmental health. Regulatory approaches they are given worldwide, as well as (eco)toxicity data available were hence thoroughly reviewed. Critical research gaps were identified particularly regarding (i) the toxic effects other than those typical of the recognized disease/disorder each toxin causes following acute exposure in humans and also in other biota; and (ii) alternative detection tools capable of being early-warning signals for aquatic toxins occurrence and therefore provide better human and environmental safety insurance. Future directions on aquatic toxins research are discussed in face of the existent knowledge, with particular emphasis on the much-needed development and implementation of effective alternative (eco)toxicological biomarkers for these toxins. The wide-spanning approach followed herein will hopefully stimulate future research more broadly addressing the environmental hazardous potential of aquatic toxins. • The occurrence of cyanobacteria and algal blooms in aquatic environments is rising, often leading to increased phytoplankton neurotoxins production. • Improved knowledge of the full toxic potential of aquatic neurotoxins for humans and also for aquatic biota is required. • The development of alternative biomarker-based methodologies are promising tools that can aid in safeguarding human and environmental health, serving as early-warning signs for neurotoxins presence and toxic effects. • The possibility of increased fatal poisonings in freshwater and marine environments amplifies the need for conducting additional research on aquatic toxins. [ABSTRACT FROM AUTHOR]

Toxic cyanobacterial blooms are a major contaminant in inland aquatic ecosystems. Furthermore, toxic blooms are carried downstream by rivers and waterways to estuarine and coastal ecosystems. Concerning marine and estuarine animal species, very little is known about how these species are affected by the exposure to freshwater cyanobacteria and cyanotoxins. So far, most of the knowledge has been gathered from freshwater bivalve molluscs. This work aimed to infer the sensitivity of the marine mussel Mytilus galloprovincialis to single as well as mixed toxic cyanobacterial cultures and the underlying molecular responses mediated by toxic cyanobacteria. For this purpose, a mussel exposure experiment was outlined with two toxic cyanobacteria species, Microcystis aeruginosa and Chrysosporum ovalisporum at 1 × 105 cells/mL, resembling a natural cyanobacteria bloom. The estimated amount of toxins produced by M. aeruginosa and C. ovalisporum were respectively 0.023 pg/cell of microcystin-LR (MC-LR) and 7.854 pg/cell of cylindrospermopsin (CYN). After 15 days of exposure to single and mixed cyanobacteria, a depuration phase followed, during which mussels were fed only non-toxic microalga Parachlorella kessleri. The results showed that the marine mussel is able to filter toxic cyanobacteria at a rate equal or higher than the non-toxic microalga P. kessleri. Filtration rates observed after 15 days of feeding toxic microalgae were 1773.04 mL/ind.h (for M. aeruginosa), 2151.83 mL/ind.h (for C. ovalisporum), 1673.29 mL/ind.h (for the mixture of the 2 cyanobacteria) and 2539.25 mL/ind.h (for the non-toxic P. kessleri). Filtering toxic microalgae in combination resulted in the accumulation of 14.17 ng/g dw MC-LR and 92.08 ng/g dw CYN. Other physiological and biochemical endpoints (dry weight, byssus production, total protein and glycogen) measured in this work did not change significantly in the groups exposed to toxic cyanobacteria with regard to control group, suggesting that mussels were not affected with the toxic microalgae. Nevertheless, proteomics revealed changes in metabolism of mussels related to diet, specially evident in those fed on combined cyanobacteria. Changes in metabolic pathways related with protein folding and stabilization, cytoskeleton structure, and gene transcription/translation were observed after exposure and feeding toxic cyanobacteria. These changes occur in vital metabolic processes and may contribute to protect mussels from toxic effects of the toxins MC-LR and CYN.

Hydrogen peroxide (H2O2) can be used as an emergency method to selectively suppress cyanobacterial blooms in lakes and drinking water reservoirs. However, it is largely unknown how environmental parameters alter the effectiveness of H2O2 treatments. In this study, the toxic cyanobacterial strain Microcystis aeruginosa PCC 7806 was treated with a range of H2O2 concentrations (0 to 10 mg/L), while being exposed to different light intensities and light colors. H2O2 treatments caused a stronger decline of the photosynthetic yield in high light than in low light or in the dark, and also a stronger decline in orange than in blue light. Our results are consistent with the hypothesis that H2O2 causes major damage at photosystem II (PSII) and interferes with PSII repair, which makes cells more sensitive to photoinhibition. Furthermore, H2O2 treatments caused a decrease in cell size and an increase in extracellular microcystin concentrations, indicative of leakage from disrupted cells. Our findings imply that even low H2O2 concentrations of 1−2 mg/L can be highly effective, if cyanobacteria are exposed to high light intensities. We therefore recommend performing lake treatments during sunny days, when a low H2O2 dosage is sufficient to suppress cyanobacteria, and may help to minimize impacts on non-target organisms.

The microbial community structures of drinking water treatment sludge (DWTS) generated for raw water (RW) from different locations and with different source types — including river water, lake water and reservoir water —were investigated using high-throughput sequencing. Because the unit operations in the six DWTPs were similar, community composition in fresh sludge may be determined by microbial community in the corresponding RW. Although Proteobacteria , Cyanobacteria , Bacteroidetes , Firmicutes , Verrucomicrobia , and Planctomycetes were the dominant phyla among the six DWTS samples, no single phylum exhibited similar abundance across all the samples, owing to differences in total phosphorus, chemical oxygen demand, Al, Fe, and chloride in RW. Three genera of potentially toxic cyanobacteria ( Planktothrix , Microcystis and Cylindrospermopsis ), and four potential pathogens ( Escherichia coli , Bacteroides ovatus , Prevotella copri and Rickettsia ) were found in sludge samples. Because proliferation of potentially toxic cyanobacteria and Rickettsia in RW was mainly affected by nutrients, while growth of Escherichia coli , Bacteroides ovatus and Prevotella copri in RW may be influenced by Fe, control of nutrients and Fe in RW is essential to decrease toxic cyanobacteria and pathogens in DWTS. [ABSTRACT FROM AUTHOR]

The application of 13C and 15N labeled phytoplankton makes it possible to directly follow the pathway and transfer of food source (cyanobacteria) into consumers (aquatic organisms), in contrast to past studies where only changes in compositions of chlorophyll-a, clearity, and nutrients were taken as the evidence for these processes. To evaluate the effect of biocontrol by aquatic organisms (aquatic plants; Iris pseudoacorus, filter feeder bivalve; Sinanodonta arcaeformis, and Unio douglasiae, macroinvertebrate; Caridina denticulate, carnivore fish; Pseudobagrus fulvidraco, Odontobutis platycephala, planktivore fish; Pseudorasbora parv, and omnivore fish; Misgurmus anguillicaudatus) on large toxigenic cyanobacteria bloom (Microcystis aeruginosa) in the freshwater ecosystem, we conducted a biomanipulation test on in situ ponds using dual stable isotope tracers (13C and 15N). As a filter feeding bivalve, S. arcaeformis could incorporate more toxic cyanobacteria cells than U. douglasiae, demonstrating its larger detoxification capacity. Also, macroinvertebrate (C. denticulate) continuously assimilated to cyanobacteria species in combination with zooplankton and detritus, probably due to detoxification capacity. Indeed, the aquatic plants (I. pseudoacorus) seem to be nutrient uptakes in water column and inhibit to light attenuation, comparing to cyanobacteria species. As a primary consumer of phytoplankton, zooplankton (Copepoda) consumed to small and edible particles which is changed from inedible toxic filamentous cyanobacteria species through the grazing efficiency by aquatic organisms. However, various kinds of fishes hardly feed on toxic cyanobacteria directly. Our result suggests that the native species, like Sinanodonta sp. and C. denticulate, are very useful bio-control organisms on toxic cyanobacteria bloom rather than carnivore, omnivore and planktivore fish. Furthermore, if an aquatic plant that can not only remove nutrients but also provide habitats to aquatic organisms (zooplankton, bivalves and shrimps) is developed, it can help control toxic cyanobacteria blooms. Therefore, it is considered that the development and establishment of habitat of useful organisms is very necessary for water quality improvement. Our biomanipulation technique may provide a key tool for efficient management and restoration of eutrophied reservoirs. [ABSTRACT FROM AUTHOR]

The lower part of the Han River, which flows through Seoul, Korea, experienced excessive toxic cyanobacterial growth in 2015. Modeling of algal bloom occurrence patterns in the lower part of this river was performed using the Environmental Fluid Dynamics Code (EFDC) to understand algal dynamics and thus better develop management alternatives. For a 71 km long river section, 1175 horizontal 2-D grid elements were developed. This grid system was determined adequate, as the maximum values of the Courant–Friedrichs–Lewy condition and orthogonality deviation were 0.5 and 20.1, respectively. Chlorophyll-a (Chl-a) was chosen as the primary indicator for the likelihood of algal blooms. Calibration and verification of EFDC were performed by comparing the model results to three years of field data collected from 2013 to 2015. Calibration accuracy was verified not only for physical variables, including the mean water level and temperature, but also for other water quality variables in various locations of the study area. To improve the prediction accuracy of Chl-a, three dominant groups of algae were considered: diatoms, green algae, and cyanobacteria. The optimum growth temperature ranges were selected based on field data for the study area. It was found necessary to apply different maximum growth rates for algal groups for the upstream and downstream regions of the study area to appropriately reflect field observations. This result indicates that more than three algal groups need to be included to improve Chl-a calibration accuracy for the study area, yet the current EFDC model can consider only up to three phytoplankton groups. Although this problem could be overcome by assigning different maximum growth rates for different regions, it may be necessary to improve EFDC so that it can include more phytoplankton groups. [ABSTRACT FROM AUTHOR]

Seasonal blooms of cyanobacteria (CB) are a typical feature of Lake Alto Flumendosa (Sardinia, Italy). The waters of this lake are used for drinking water supply, for agricultural and industrial uses, and fish farming activities. Since cyanotoxins are not monitored in edible organisms, diet could be a relevant route of human exposure. CB also represent a threat for the health of wild and domestic animals that use lake water for beverage. Therefore, to characterize the CB community and assess the risk for human and animal population, CB dynamic, mcyB+ fraction, and microcystins (MCs) concentration have been followed monthly for 18 months, in three stations. Results confirmed the presence of several toxigenic species. Planktothrix rubescens dominated between August 2011 and April 2012 (3.5×106 cells L-1), alternating with Woronichinia naegeliana (8×106 cells L-1) and Microcystis botrys (9×105 cells L-1). Dolichospermum planctonicum was always present at low densities (104 cells L-1). MCs were detected, at values well below the 1 µg L-1 threshold of WHO for drinking water. The molecular analysis of mcyB gene for P. rubescens indicated the presence of a persistent toxic population (average 0.45 mcyB/16S rDNA). Highly significant linear regressions were found between P. rubescens and the sum of the demethylated MC variants, and between M. botrys and the sum of MC-LR and MC-LA, also when co-occurring, suggesting that these two species were responsible for different MC patterns production. The regression lines indicated a quite stable MC cell quota. However, in some spotted samples very different values were obtained for both MC concentrations and cell quota (from 10-fold lower to 30-40-fold higher than the ‘average’) showing an unexpected significant variability in the rate of toxin production. The relatively low cell densities during the monitoring period is consistent with the low-to absent MC contamination level found in trout muscle; however, the analytical method was affected by low recovery, probably due to MC-protein binding. Our results show that, during the study period, no risk of exposure for the human and animal population occurred. However, the persistence of a complex CB community characterised by a significant toxic fraction suggests the need for periodic monitoring activity. Particularly, the hidden deep summer P. rubescens blooms, located where water is taken for drinking water supply, and M. botrys, able to produce the most toxic MC variants with high cell quota, should be kept under control. The documentation and interpretation of sudden changes in toxins concentrations deserve special attention. This is particularly relevant in proximity of fish farming plants and water catchment sites.

The effects of weirs on fish and other biological communities have garnered considerable study, whereas the effects of weirs on community composition of toxic cyanobacteria have not yet been well documented. In this study, temporal and spatial variations in species composition and the abundance of potentially toxic cyanobacteria were investigated in the riverine regions of the temperate Youngsan River estuary, where two weirs have recently been constructed. Four stations were sampled 0.5 m below the surface monthly along the channel of the upper river from May 2014 to April 2015 to explore cyanobacterial composition and abundance, while physicochemical and biological parameters were measured to elucidate possible mechanisms controlling these dynamics. Two stations were located upstream at free-flowing sites, and the other stations were located downstream at impounded sites near the weirs. Twenty-eight cyanobacterial species were identified, seven of which were potentially toxic: Microcystis sp., M. aeruginosa, M. flos-aquae, Dolichospermum sp., Aphanocapsa sp., Oscillatoria sp. and Phormidium sp. Microcystis sp. was the most abundant in June 2014 at the lowest station near the weir. Meanwhile, Phormidium sp. occurred at low abundance throughout the study period, except during the winter months, when its abundance was elevated. The interactive forward selection method highlighted dissolved inorganic nitrogen and zooplankton abundance as explanatory variables for this observed variation, but their effects on cyanobacterial growth are unclear. However, temperature was the major determinant for the temporal variation in cyanobacterial populations. Cluster analysis showed that the downstream stations near the weirs had a high similarity of potentially toxic cyanobacteria. Significantly higher abundance, especially of Microcystis sp., was also recorded at the impounded sites suggesting that the presence of weirs might affect variations in toxic cyanobacterial communities. [ABSTRACT FROM AUTHOR]

The anti-algal activity of five macrophyte extracts on the cyanobacteriumMicrocystis aeruginosain Egypt was investigated in 2013. Extract activity varied according to plant type, extracting solvent and its concentration. The highest inhibitory activity was achieved with ethanol extract at a concentration of 80 mg l−1, followed by chloroformic extracts, at 60 mg l−1. Methanolic extracts ofEichhornia crassipesandPolygonum tomentosuminhibited growth ofMicrocystis aeruginosaat all concentrations. Acetonic extracts inhibited algal growth at 60 mg l−1, except for the extract ofCeratophyllum subdemersum, which showed stimulation ofM. aeruginosagrowth.Eichhornia crassipesethanolic extract exerted the most powerful inhibition by more than five-fold, 570.17%, followed by those ofP. tomentosum, Saccharum spontaneum, Ceratophyllum demersumandC. subdemersum, 559.48, 553.99, 544.11 and 366.51%, respectively. Phytochemical screening for the tested plant extracts revealed the presence of biologically active substances of different concentrations, withP. tomentosumhaving the highest polyphenols, 1.95% of dry weight. [ABSTRACT FROM PUBLISHER]

Bloom-forming microalgae and hypoxia are considered as the two main co-occurring stressors associated with eutrophication. How these two stressors might alter the sail mussel exposed to toxic cyanobacteria and hypoxia has not been well evaluated histophysiologically. Therefore, the present study was designed to evaluate the combined effects of the harmful cyanobacteria ( Microcystis aeruginosa ) and hypoxia on the histopathological alterations in the gill, digestive gland, and stomach of an ecologically and economically important mussel species inhabiting lakes and reservoirs, the triangle sail mussel ( Hyriopsis cumingii ). To evaluate the histophysiological changes due to the stressors, a 2 × 2 factorial design with four treatments was adopted: two dissolved oxygen levels (hypoxia: 1 mg O 2 l − 1 ; normoxia: 6 mg O 2 l − 1 ) and two treatments, one with 0% and another with 100% (1.8 × 10 7 cell ml − 1 ca. 50 mg l − 1 ) cell biomass of toxic M. aeroginosa . The non-toxic green alga ( Chlorella vulgaris ) was supplemented to maintain the same algal biomass in the four treatments. Samples from the treatments were collected on days 0, 3, 5, 7, 14, and 21. The microcystin content in sail mussels exposed to M. aeruginosa increased over the entire experimental span, under both normoxia and hypoxia, but was significantly lower in mussels under hypoxic conditions. Pathological alterations were observed in the gills, digestive diverticula and stomach of mussels under hypoxia, when fed 100% M. aeruginosa diet, and when intoxicated with M. aeruginosa under hypoxia. Hyperplasia, exfoliation of latero-frontal cilia, filament fusion, and epithelial desquamation of filaments in the gills were observed following 7 days of exposure to M. aeruginosa and hypoxia. After 7 days of exposure, the damage in the gills, digestive gland, and stomach increased. Hypoxia induced more severe effects in the gill structures than the harmful alga, whereas the digestive gland was more affected by exposure to M. aeruginosa . The stomach, however, was equally affected by both stressors. Results of this preliminary study highlight the need for further in depth studies on the combined effect of toxic cyanobacteria and hypoxia on the triangle sail mussel, and the potential implications for the freshwater pearl production in China. Statement of relevance Hyriopsis cumingii has been considered as an aquaculture species for pearl production in China. In recent years, the mussels have been often suffered from hypoxia and toxic algae, but the effects of Microcystis aeruginosa associated with hypoxia on the morphological changes of selected organs such as gill, digestive gland and stomach are unclear. This study just clarified that the selected tissues of H. cumingii were more severely affected by the both stressors, which may clarify how the toxic algae and hypoxia cause some diseases in the mussel H. cumingii . [ABSTRACT FROM AUTHOR]

Seasonal blooms of cyanobacteria (CB) are a typical feature of Lake Alto Flumendosa (Sardinia, Italy). The waters of this lake are used for drinking water supply, for agricultural and industrial uses, and fish farming activities. Since cyanotoxins are not monitored in edible organisms, diet could be a relevant route of human exposure. CB also represent a threat for the health of wild and domestic animals that use lake water for beverage. Therefore, to characterize the CB community and assess the risk for human and animal population, CB dynamic, mcyB+ fraction, and microcystins (MCs) concentration have been followed monthly for 18 months, in three stations. Results confirmed the presence of several toxigenic species. Planktothrix rubescens dominated between August 2011 and April 2012 (3.5×106 cells L-1), alternating with Woronichinia naegeliana (8×106 cells L-1) and Microcystis botrys (9×105 cells L-1). Dolichospermum planctonicum was always present at low densities (104 cells L-1). MCs were detected, at values well below the 1 µg L-1 threshold of WHO for drinking water. The molecular analysis of mcyB gene for P. rubescens indicated the presence of a persistent toxic population (average 0.45 mcyB/16S rDNA). Highly significant linear regressions were found between P. rubescens and the sum of the demethylated MC variants, and between M. botrys and the sum of MC-LR and MC-LA, also when co-occurring, suggesting that these two species were responsible for different MC patterns production. The regression lines indicated a quite stable MC cell quota. However, in some spotted samples very different values were obtained for both MC concentrations and cell quota (from 10-fold lower to 30-40-fold higher than the 'average') showing an unexpected significant variability in the rate of toxin production. The relatively low cell densities during the monitoring period is consistent with the low-to absent MC contamination level found in trout muscle; however, the analytical method was affected by low recovery, probably due to MC-protein binding. Our results show that, during the study period, no risk of exposure for the human and animal population occurred. However, the persistence of a complex CB community characterised by a significant toxic fraction suggests the need for periodic monitoring activity. Particularly, the hidden deep summer P. rubescens blooms, located where water is taken for drinking water supply, and M. botrys, able to produce the most toxic MC variants with high cell quota, should be kept under control. The documentation and interpretation of sudden changes in toxins concentrations deserve special attention. This is particularly relevant in proximity of fish farming plants and water catchment sites. [ABSTRACT FROM AUTHOR]

During assessment of water quality in the lake Kotokelskoe, we observed some cyanobacteria that forming harmful to human and animal toxins. According to the chlorophyll a content, the lake Kotokelskoe is eutrophic with high productivity of phytoplankton. But microbiological parameters such as total number of microorganisms and saprophytes cause to classify this lake as «polluted waters». Preparation. «Baikal EM 1» is actively involved to the processes of self-purification of water. It could provide decreasing of chlorophyll content total number of microorganisms in aquarium water.

The cyanobacterium Cylindrospermopsis raciborskii is capable of producing toxins including saxitoxin (STX). Few studies have verified the influence of environmental variables on the production of STX and most have only been studied in the laboratory. The goal of this work was to identify the abiotic variables related to STX concentration in situ . The relationship among STX concentration and the physical variables, nutrients and chlorophyll-a (chl-a) concentration was examined in a meso-oligotrophic subtropical coastal lake dominated by C. raciborskii . A generalized linear model was developed, incorporating all variables measured monthly over a 45-month monitoring period. Conductivity and dissolved inorganic nitrogen (DIN) concentration provided the greatest explanatory power for STX concentration in situ . Previous studies suggested that C. raciborskii cells exposed to stress associated with higher ionic concentrations appear to activate the biosynthesis of STX suggesting that STX can elicit changes cell permeability and may contribute to the homeostasis of this organism. An increase of DIN concentration results in a higher concentration of STX which may be related to a reduced metabolic demand, since the uptake of inorganic nitrogen requires less energy than N 2 -fixation. Thus, increased DIN can favor the growth of C. raciborskii population or improve cellular homeostasis, both potentially increasing STX concentration in the aquatic system, which was observed through a delayed response pattern. The developed model, while providing only a moderate predictive power, can assist in the understanding of the environmental variables associated with increases in STX concentration, and in monitoring and minimizing the risks of toxic blooms. [ABSTRACT FROM AUTHOR]

Vico Lake, a volcanic meso-eutrophic lake in Central Italy, whose water is used for drinking and recreational activities, experienced the presence of the microcystins (MC) producing cyanobacterium Planktothrix rubescens . In order to assess the human health risks and to provide the local health authorities with a scientific basis for planning tailored monitoring activities, we studied P. rubescens ecology and toxicity for two years. P. rubescens generally dominated the phytoplankton community, alternating with Limnothrix redekei , potentially toxic. P. rubescens was distributed throughout the water column during winter; in summer it produced intense blooms where drinking water is collected (−20 m); here MC were detected all year round (0.5–5 μg/L), with implications for drinking water quality. In surface waters, MC posed no risk for recreational activities in summer, while in winter surface blooms and foams (containing up to 56 μg MC/L) can represent a risk for people and children practicing water sports and for animals consuming raw water. Total phosphorus, phosphate and inorganic nitrogen were not relevant to predict densities nor toxicity; however, a strong correlation between P. rubescens density and aminopeptidase ectoenzymatic activity, an enzyme involved in protein degradation, suggested a role of organic nitrogen for this species. The fraction of potentially toxic population, determined both as mcyB + /16SrDNA (10–100%) and as the MC/ mcyB + cells (0.03–0.79 pg MC/cell), was much more variable than usually observed for P. rubescens . Differently from other Italian and European lakes, the correlation between cell density or the mcyB + cells and MC explained only ∼50 and 30% of MC variability, respectively: for Vico Lake, monitoring only cell or the mcyB + cell density is not sufficient to predict MC concentrations, and consequently to protect population health. Finally, during a winter bloom one site has been sampled weekly, showing that monthly sampling during such a phase could greatly underestimate the ‘hazard’. Our results highlight the need to adopt a stepwise monitoring activity, considering the lake and the cyanobacteria specific features. This activity should be complemented with communication to the public and involvement of stakeholders. [ABSTRACT FROM AUTHOR]

Many urban ponds in The Netherlands and other countries suffer from eutrophication, resulting in harmful algal blooms which are often dominated by cyanobacteria. A sufficient reduction of nutrients, as prerequisite to mitigate cyanobacterial blooms in urban ponds, is not always feasible. Water managers are in need for applicable alternatives to mitigate these cyanobacterial blooms. The quagga mussel ( Dreissena rostriformis bugensis ) is a rapidly expanding bivalve species in many standing waters and rivers in The Netherlands. Because quagga mussels feed on algae, they could become a useful tool in controlling harmful algal blooms in urban ponds if provided with the appropriate substrate. We tested the hypothesis that quagga mussels can reduce phytoplankton biomass and induce a clear water state in a shallow hypertrophic urban pond. We executed an in situ enclosure experiment using eight enclosures (750 L) in an urban pond: four enclosures contained quagga mussels (0.3 g ww L −1 ), and four control enclosures were set up without mussels. We used artificial substrate for the breeding of mussels and the transfer from the breeding location to the experimental site. In contrast to the controls, the enclosures with mussels showed significantly lower concentrations of total chlorophyll- a (2.4 μg L −1 in mussel enclosures versus 84.1 μg L −1 in controls), cyanobacterial chlorophyll- a (1.0 μg L −1 versus 7.3 μg L −1 ) and total phosphorus (0.08 mg L −1 versus 0.17 mg L −1 ), and had higher transparency (>0.80 m in mussel enclosures versus 0.57 m in controls) and higher soluble reactive phosphorus concentration (0.03 mg L −1 versus <0.01 mg L −1 ). No effect of the mussels on microcystin concentrations was shown. The results show that quagga mussels are able to reduce the phytoplankton biomass in a hypertrophic urban pond, including cyanobacteria and induce a clear water state. We conclude that quagga mussels can be a promising tool in controlling algal blooms in urban ponds, in particular when a sufficient reduction of nutrients is not feasible. A preferred next step in the scaling up of the method is the determination of long-term effectiveness and side-effects in a controlled application in an urban pond. Because the quagga mussel is an invasive alien species, new introductions should be considered carefully and water purification using quagga mussels is preferably applied in water systems where the species is already present. [ABSTRACT FROM AUTHOR]