Cyanobacteria In Water Bodies Research Articles

Стрессорное воздействие биоцидных метаболитов актинобактерии Streptomyces geldanamycininus Z374 на цианобактерии Microcystis aeruginosa

Over the past decades, as a result of anthropogenic pollution and global warming, the frequency, intensity and geographical distribution of the mass development of microalgae and cyanobacteria in water bodies have significantly increased. The Microcystis species are responsible for most cases of the cyanobacterial blooms in freshwater bodies worldwide. Microcystis aeruginosa is the most commonly observed of them. In this work, we assessed the stress effect of isolated from actinobacteria Streptomyces geldanamycininus cyanocidal crude biocide Z374 (CB Z374) on the cyanobacteria M. aeruginosa. The results showed that CB Z374 significantly inhibited M. aeruginosa biomass. The CB Z374 half maximal effective concentration (EC50) for M. aeruginosa after 96 hours of treatment was 5 mg/L. The growth of M. aeruginosa with CB Z374 is characterized by an increase in the duration of the lag-phase, a decrease in the specific growth rate and biomass yield compared to the control. CB Z374 caused oxidative stress in cyanobacteria cells, determined by the elevated levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) up to 1.6 times, as well as an increased permeability of M. aeruginosa cell membranes by 1.5 times. The levels of superoxide dismutase (SOD) and catalase (CAT) activities and reduced glutathione (GSH) content raised in response to oxidative stress. M. aeruginosa growth inhibition was accompanied by a photosynthesis modification: the photosynthetic pigments phycobiliproteins and carotenoids content increases by 2.3 and 1.6 times respectively and the chlorophyll a content decreases by 1.2 times. CB Z374 inhibited M. aeruginosa photosynthesis, which was expressed in a decline in the maximum quantum efficiency of photosystem II – Fv/Fm by 10% and a reduction in the electron transfer rate (ETR) by 18%. We assume that oxidative stress and, as a result, cell membranes damage and photosynthesis inhibition are the main mechanisms of the cyanocidal action of CB Z374 on M. aeruginosa.

Моделирование способов управления динамикой цианобактериального цветения с применением воздушных и надводных робототехнических средств

The paper discusses the problem of water areas contaminated with cyanobacteria and ways to eliminate it through the use of robotic means. Laser radiation has the ability to significantly suppress the vital activity of both cyanobacteria and a number of studied pathogenic bacteria, fungal viruses and other microorganisms. The parameters of laser radiation were modeled with an assessment of the inhibitory effect on cyanobacteria in water bodies. Examples of created attachments with laser emitters, transport unmanned aerial vehicles and surface vehicles used in studies to control the dynamics of cyanobacterial blooms are presented.

Statistical evaluation of trends of water quality monitoring parameters relevant to cyanobacterial blooms in the urban tropical reservoir.

The accelerated growth of cyanobacteria in water bodies is a global critical environmental issue caused by continuous discharges of effluents into the environment that are rich in phosphorus and nitrogen. So, cyanobacteria have found propitious conditions for proliferation, provoking significant ecological imbalances. Cyanobacteria produce cyanotoxins, which are harmful to life, and compounds like 2-methylisoborneol and geosmin that affect water's taste and odor. This study analyzed a long-term database of important environmental parameters from a tropical reservoir in São Paulo State, Brazil. The statistical methods of correlation matrices and principal component analysis were used. Data analysis revealed a significant relationship between cyanobacteria growth and high levels of phosphate and nitrogen. Furthermore, positive correlations were found among concentrations of biocidal elements like antimony, arsenic, and selenium related to cyanobacterial bloomings. These correlations can be attributed to agricultural wastewaters and/or possible algicide used to control these microorganisms.

MICRОCYSTIS AЕRUGINОSA AS A SОURCЕ ОF BIОLОGICAL HAZARDS IN WATЕR RЕSЕRVОIRS ОF UKRAINЕ

Introduction. Phytoplankton, including cyanobacteria, is ubiquitous in various types of reservoirs, and it plays a crucial role in aquatic ecosystems. Among phytoplankton, cyanobacteria, considered one of the most primitive chlorophyll-containing organisms, have a significant presence in both standing freshwater lakes and seawater. Microcystis aeruginosa (M. aeruginosa), a common cyanobacterial species, is known for forming harmful “water blooms” that pose serious ecological and health risks. The rise of urbanization in Ukraine and the consequences of the war has intensified the eutrophication and cyanobacterial blooms in drinking water sources, necessitating improved detection and prevention strategies.
 The aim of this study was to develop modern and effective methods for diagnosing microcystin-containing cyanobacteria, particularly M. aeruginosa, to address biological hazards in Ukrainian water reservoirs.
 Materials and methods. Water samples were collected from a stagnant town lake in the Ivano-Frankivsk region during both summer and winter seasons to account for seasonal fluctuations in cyanobacteria content. Cyanobacteria were isolated from water samples and subjected to DNA extraction. PCR analysis using specific oligonucleotide primers targeted the 16S rRNA gene of M. aeruginosa.
 The results revealed the presence of 16S rRNA products in all water samples, irrespective of the season, indicating a consistent distribution of M. aeruginosa in the lake throughout the year.
 Discussion. We found cyanobacteria in all water samples regardless of the season. This indirectly suggests the presence of anthropogenic pollution, which helps maintain a consistent concentration of cyanobacteria throughout the year.
 In conclusion, the developed PCR-based method offers a sensitive and specific means of detecting M. aeruginosa, enabling comprehensive investigations across various water reservoirs. The presence of cyanobacteria in water bodies, while natural, can serve as an indicator of anthropogenic pollution, particularly nitrogen and phosphorus. This methodology holds promise for safeguarding Ukraine's drinking water sources and managing the impact of anthropogenic pollution, ultimately ensuring public health through effective planning and preventive measures.

Effects of Lactobacillus plantarum Ep-M17 on growth, immunity and intestinal microbiota of Penaeus vannamei under Microcystin-LR stress

Microcystins (MCs) are biologically active cyclic heptapeptide compounds released by cyanobacteria in water bodies, and MC-LR is one of the most widespread and toxic isoforms. It frequently poses a serious threat to Penaeus vannamei aquaculture. Our previous study revealed that the supplementation of Lactobacillus plantarum Ep-M17 has a probiotic effect on P. vannamei health and whether Ep-M17 can alleviate the stressful effects of MC-LR on shrimp remains unclear. Therefore, in the present work, shrimp were fed MC-LR alone or combined with Ep-M17 for six weeks, and then evaluated the effects on histology, enzyme activity, gene expression, and intestinal flora. The results showed that MC-LR stress lead to slow growth and reduced survival rates in shrimp. However, feeding Ep-M17 significantly increased both the growth rate and survival rate. Meanwhile, MC-LR stress caused severe tissue damage in the hepatopancreas and intestines of shrimp, but Ep-M17 significantly reduced the toxic effects and protected the integrity of these tissues. Additionally, Ep-M17 significantly enhanced the activities of antioxidant enzymes and digestive enzymes, and induced higher expression of immune-related genes, thereby promoting the digestive and immune responses in shrimp. Furthermore, MC-LR stress disrupted the intestinal flora in shrimp intestines, while the use of Ep-M17 significantly increased the abundance of immune- and metabolism-related bacteria and inhibited the growth of pathogenic bacteria to maintain intestinal flora balance and intestinal health. In conclusion, our results indicate that Ep-M17 can reduce the toxic effect of MC-LR on shrimp and has a positive function in the prevention and control of shrimp diseases caused by MC-LR.

Deep Cyanobacteria Layers: An Overlooked Aspect of Managing Risks of Cyanobacteria.

The risk of human exposure to cyanotoxins is partially influenced by the location of toxin-producing cyanobacteria in waterbodies. Cyanotoxin production can occur throughout the water column, with deep water production representing a potential public health concern, specifically for drinking water supplies. Deep cyanobacteria layers are often unreported, and it remains to be seen if lower incident rates reflect an uncommon phenomenon or a monitoring bias. Here, we examine Sunfish Lake, Ontario, Canada as a case study lake with a known deep cyanobacteria layer. Cyanotoxin and other bioactive metabolite screening revealed that the deep cyanobacteria layer was toxigenic [0.03 μg L-1 microcystins (max) and 2.5 μg L-1 anabaenopeptins (max)]. The deep layer was predominantly composed of Planktothrix isothrix (exhibiting a lower cyanotoxin cell quota), with Planktothrix rubescens (exhibiting a higher cyanotoxin cell quota) found at background levels. The co-occurrence of multiple toxigenic Planktothrix species underscores the importance of routine surveillance for prompt identification leading to early intervention. For instance, microcystin concentrations in Sunfish Lake are currently below national drinking water thresholds, but shifting environmental conditions (e.g., in response to climate change or nutrient modification) could fashion an environment favoring P. rubescens, creating a scenario of greater cyanotoxin production. Future work should monitor the entire water column to help build predictive capacities for identifying waterbodies at elevated risk of developing deep cyanobacteria layers to safeguard drinking water supplies.

Monitoring of cyanobacteria using derivative spectrophotometry and improvement of the method detection limit by changing pathlength

Abstract Effective monitoring tools and methods are needed for the early detection and management of cyanobacteria in water bodies to minimize their harmful impacts on the environment and public health. This research investigated changing the cuvette pathlength (10-, 50-, and 100-mm) to improve the detection of cyanobacteria using UV-Vis spectrophotometry with subsequent application of derivative spectrophotometry and Savitzky-Golay (S-G) transformation. A non-toxigenic strain of blue-green cyanobacteria, Microcystis aeruginosa (CPCC 632), and a green algae strain for comparison, Chlorella vulgaris (CPCC 90), were studied in a wide range of concentrations (955,000 to 1855 cells/mL). In each concentration range, method detection limits were established with absorbance measurements and S-G first derivative of absorbance using 10-, 50-, and 100-mm cuvette pathlengths. Increasing the cuvette pathlength from 10 to 100 mm resulted in a 15-fold improvement in sensitivity with absorbance and a 13-fold improvement with S-G first derivative of absorbance for M. aeruginosa. Overall, adoption of 100 mm pathlength and application of S-G derivative spectra improved the method detection limit for M. aeruginosa from 337,398 to 4916 cells/mL, which is below the WHO guideline for low probability of adverse health effects (<20,000 cells/mL). Similarly, the detection limit for C. vulgaris was improved from 650,414 to 11,661 cells/mL. The results also showed that spectrophotometry could differentiate M. aeruginosa from C. vulgaris based on the variations in their pigment absorbance peaks.

High sensitive single chain variable fragment screening from a microcystin-LR immunized mouse phage antibody library and its application in immunoassay

Microcystin-LR (MC-LR) is one of common high-toxic biotoxins produced by cyanobacteria in waterbody. A high sensitive and convenient detection method is necessary for monitoring for MC-LR. To establish a high sensitive indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) based on single chain variable fragment (scFv) for detecting MC-LR, 16 positive anti-MC-LR phage scFv particles were screened out from a MC-LR-immunized mouse phage scFv library, which was successfully constructed with the capacity of 8.67 × 107 CFU/mL. The most positive anti-MC-LR phage scFv (MscFv7) was successfully expressed in Escherichia coli (E.coli) HB2151. The molecular weight (M.W.) of expressed protein was about 30 kDa, and the concentration of purified protein was 512.6 μg/mL analyzed by SDS-PAGE and protein quantitative respectively. The IC-ELISA based on MscFv7-scFv for MC-LR shows a half-maximum inhibition (IC50) of 0.471 μg/L and a limit of detection (LOD) of 0.044 μg/L, which is below the maximum residue limit standard (MRLs) of 1.0 μg/L in drinking water. The MscFv7-scFv has a strong cross-recognition for MC-RR and MC-YR with cross-reactivity (CRs) of 93.1% and 85.9%, respectively, but weak for MC-LW with that of 9.7%, even non-recognition for MC-WR, MC-LF and MC-LY. The recovery rates of IC-ELISA to detect MC-LR spiked in different cleanliness of water samples were 81.2–106.3% with CVs of 2.62–10.22% at intra-assay and inter-assay. The results showed that we obtained a high sensitive anti-MC-LR scFv, and the established IC-ELISA based on MscFv7-scFv should be promising for ultrasensitive monitoring MC-LR, MC-RR and MC-YR in water samples.

Preliminary Study to Find Occurrence and Dynamics of Toxic Cyanobacteria in Nuwara wewa and Nachchaduwa wewa, Two Man-made Reservoirs in Sri Lanka

Bloom of cyanobacteria in water bodies causes devastating problems to the ecosystem and humans when they depend on these waters for drinking purpose. Microcystin and nodularin, produced by some cyanobacteria, are toxic for human and many other aquatic organisms. Nuwara wewa and Nachchaduwa wewa are two important reservoirs supplying water for drinking purpose in addition to agricultural use. Therefore, preliminary study was conducted to evaluate these reservoirs for the presence of toxic cyanobacteria and their dynamics is of importance to take proper measures to control cyanobacterial growth and to ensure supply of quality water for human drinking purpose. Water samples were collected for 12 months from both reservoirs and physic-chemicals parameters of water were also recorded. Correlations between the physico-chemical parameters of water and the cyanobacterial density were established. Toxic cyanobacteria were isolated and identified using conventional and molecular methods. 16S rRNA gene and mcy-A gene were targeted for molecular identification using PCR. Cyanobacterial density had strong positive correlations with some physico-chemical parameters such as pH, temperature and dissolved oxygen in both reservoirs. These parameters can be used as good indicators to evaluate the condition these reservoirs with respect to cyanobacterial bloom. Some cyanobacterial isolates recovered from both reservoirs harboured mcy-A gene, showing the potential of microcystin production.

The predominant phytoplankton of Pseudoanabaena holding specific biosynthesis gene-derived occurrence of 2-MIB in a drinking water reservoir.

With the increasing occurrence of water eutrophication and blooms, earthy-musty odor problems caused by cyanobacteria have been more and more apparent. These problems have a serious impact on aquatic ecosystems and drinking water safety and become one of the priorities of the water environment researches and managements. In the present study, genes associated with 2-MIB synthesis in cyanobacteria were studied by systematic investigation on molecular characterization and quantity of 2-MIB-producing cyanobacteria in China. Our results founded that Pseudoanabaena is an important 2-MIB-producing phytoplankton and predominant in summer in Qingcaosha reservoir, and the copy number of mic and 2-MIB concentration have strongly positive correlation. We also demonstrated that abundance of mic in water was significant correlation with that in sediment. These results will help us to understand the main taxa of the odoriferous cyanobacteria in the water bodies in China, understand the genetic basis of the odor substances in the cyanobacteria. Rapid, reliable monitoring and ecological research methods for the production of odor cyanobacteria in water bodies can be established based on these results.

Multisource data for seasonal variability analysis of cyanobacteria in a tropical inland aquatic environment

Cyanobacterial blooms are related to eutrophic conditions that compromise the many uses of reservoirs. Thus, quick and effective methods for detecting the abundance of cyanobacteria in waterbodies are needed to complement conventional laboratory methods. In addition, inadequate control techniques that are applied at times of high cyanobacterial concentrations can cause the cells to lyse and release toxins into the water. In the present study we investigated the behaviour of cyanobacteria by determining phycocyanin and chlorophyll concentrations, using spectroradiometric and fluorometric techniques, in three field campaigns performed at the Nova Avanhandava Reservoir, Brazil. The sampling rate and favourable season for data collected had been determined previously by remote sensing analysis. Seasonal estimates of cyanobacteria were made because fluorometric sensors were able to record low concentrations, whereas the spectral analyses only detected phycocyanin at higher concentrations. Results of spectral analyses highlighted the subtle spectral characteristics indicating the presence of phycocyanin, even without a clear definition of the diagnostic features in the reflectance curve. Therefore, multiscale remote sensing complemented by fluorometric analysis and relevant environmental variables is an effective approach for monitoring cyanobacteria in Brazilian inland waters.

ACQUA: Automated Cyanobacterial Quantification Algorithm for toxic filamentous genera using spline curves, pattern recognition and machine learning

Toxigenic cyanobacteria are one of the main health risks associated with water resources worldwide, as their toxins can affect humans and fauna exposed via drinking water, aquaculture and recreation. Microscopy monitoring of cyanobacteria in water bodies and massive growth systems is a routine operation for cell abundance and growth estimation. Here we present ACQUA (Automated Cyanobacterial Quantification Algorithm), a new fully automated image analysis method designed for filamentous genera in Bright field microscopy. A pre-processing algorithm has been developed to highlight filaments of interest from background signals due to other phytoplankton and dust. A spline-fitting algorithm has been designed to recombine interrupted and crossing filaments in order to perform accurate morphometric analysis and to extract the surface pattern information of highlighted objects. In addition, 17 specific pattern indicators have been developed and used as input data for a machine-learning algorithm dedicated to the recognition between five widespread toxic or potentially toxic filamentous genera in freshwater: Aphanizomenon, Cylindrospermopsis, Dolichospermum, Limnothrix and Planktothrix. The method was validated using freshwater samples from three Italian volcanic lakes comparing automated vs. manual results. ACQUA proved to be a fast and accurate tool to rapidly assess freshwater quality and to characterize cyanobacterial assemblages in aquatic environments.

Hepatotoxic microcystin removal using pumice embedded monolithic composite cryogel as an alternative water treatment method

Microcystins are the most commonly encountered water-borne cyanotoxins which present short- and long-term risks to human health. Guidelines at international and national level, and legislation in some countries, have been introduced for the effective health risk management of these potent hepatotoxic, tumour-promoters.The stable cyclic structure of microcystins and their common production by cyanobacteria in waterbodies at times of high total dissolved organic carbon content presents challenges to drinking water treatment facilities, with conventional, advanced and novel strategies under evaluation. Here, we have studied the removal of microcystins using three different forms of pumice particles (PPs), which are embedded into macroporous cryogel columns.Macroporous composite cryogel columns (MCCs) are a new generation of separation media designed to face this challenging task. Three different MCCs were prepared by adding plain PPs, Cu2+-attached PPs and Fe3+-attached PPs to reaction media before the cryogelation step. Column studies showed that MCCs could be successfully used as an alternative water treatment method for successful microcystin removal.

Biomanipulation in mesocosms using silver carp in two Chinese lakes with distinct trophic states

Artificial enhancement of lakes using filter-feeding silver carp is a technique that is widely used to manipulate and/or promote fisheries' production in Chinese lakes. To evaluate the impact of this enhancement on nutrient cycling in the water column, we analyzed two silver carp biomass gradient testing sites by stocking experimental enclosures within Lake Taihu (eutrophic) with 0, 35, 70 and 150gm−3 of silver carp biomass and those within Lake Erhai (mesotrophic) with 0, 20, 50 and 100gm−3 of silver carp biomass. Total phosphorus and dissolved nitrogen were obviously influenced by the fish density. At relatively low densities, the silver carp were able to graze for particles of food directly, resulting in a decline in phosphorus and chlorophyll-a levels within the Lake Taihu enclosures. When fish were introduced to the Lake Erhai enclosures, chlorophyll-a levels increased. Increased dissolved nitrogen levels were recorded in the Lake Taihu enclosures during the experiment, while the enhanced uptake of nutrients by increased algae resulted in decreased dissolved nitrogen levels in the Lake Erhai enclosures. We hypothesize that although silver carp could potentially reduce cyanobacteria in water bodies with large algal blooms, the relatively small change in fish in Lake Taihu is still too minor to control severe algal blooms. In relatively clean water bodies such as Lake Erhai, artificial ecological enhancement using silver carp should be evaluated carefully before action is taken in order to assess the risk of increasing small algal blooms and nutrients.

Separation of Microcystin-LR by Cyclodextrin-Functionalized Magnetic Composite of Colloidal Graphene and Porous Silica.

Microcystin-LR belongs to the family of microcystins produced by cyanobacteria and known to be the most toxic of this family. Existence of cyanobacteria in water bodies leads to the contamination of drinking water with microcystin-LR and thus their separation is essential for an advanced water purification system. Here we report functional nanocomposite-based selective separation of microcystin-LR from contaminated water. We have synthesized cyclodextrin-functionalized magnetic composite of colloidal graphene and porous silica where the cyclodextrin component offers host-guest interaction with microcystin-LR and the magnetic component offers easier separation of microcystin-LR from water. High surface area and large extent of chemical functional groups offer high loading (up to 18 wt %) of cyclodextrin with these nanocomposites, and the dispersible form of the nanocomposite offers easier accessibility of cyclodextrin to microcystin-LR. We have shown that microcystin-LR separation efficiency is significantly enhanced after functionalization with cyclodextrin, and among all the tested cyclodextrins, γ-cyclodextrin offers the best performance. We have also found that graphene-based nanocomposite offers better performance over porous silica-based nanocomposite due to better accessibility of cyclodextrins for interaction with microcystin-LR. The proposed graphene-based functional nanocomposite is environment friendly, reusable, and applicable for advanced water purification.

Cyanobacteria in aquatic ecosystems in Serbia: effects on water quality, human health and biodiversity

Cyanobacterial blooms and toxins (cyanotoxins) in both natural and controlled waterbodies are of worldwide concern. This paper presents a review of 130 years of research on the biodiversity, occurrence and toxicity of cyanobacteria in waterbodies throughout Serbia, as well as their effects on water quality and human health. Data on the occurrence of particular cyanotoxins over more recent years are also collated. Data from over 70 sources, including research articles, project reports, conference abstracts, dissertations, books, annual and news reports are summarized. This survey provides a valuable resource for current and future assessments of cyanobacterial and cyanotoxin occurrence and abundance in Serbian waterbodies, and for management solutions where ecosystems and human health are jeopardized.

Hyperspectral remote sensing of cyanobacterial pigments as indicators for cell populations and toxins in eutrophic lakes

The growth of mass populations of toxin-producing cyanobacteria is a serious concern for the ecological status of inland waterbodies and for human and animal health. In this study we examined the performance of four semi-analytical algorithms for the retrieval of chlorophyll a (Chl a) and phycocyanin (C-PC) from data acquired by the Compact Airborne Spectrographic Imager-2 (CASI-2) and the Airborne Imaging Spectrometer for Applications (AISA) Eagle sensor. The retrieval accuracies of the semi-analytical models were compared to those returned by optimally calibrated empirical band-ratio algorithms. The best-performing algorithm for the retrieval of Chl a was an empirical band-ratio model based on a quadratic function of the ratio of reflectance at 710 and 670 nm ( R 2 = 0.832; RMSE = 29.8%). However, this model only provided a marginally better retrieval than the best semi-analytical algorithm. The best-performing model for the retrieval of C-PC was a semi-analytical nested band-ratio model ( R 2 = 0.984; RMSE = 3.98 mg m − 3). The concentrations of C-PC retrieved using the semi-analytical model were correlated with cyanobacterial cell numbers ( R 2 = 0.380) and the particulate and total (particulate plus dissolved) pools of microcystins ( R 2 = 0.858 and 0.896 respectively). Importantly, both the empirical and semi-analytical algorithms were able to retrieve the concentration of C-PC at cyanobacterial cell concentrations below current warning thresholds for cyanobacteria in waterbodies. This demonstrates the potential of remote sensing to contribute to early-warning detection and monitoring of cyanobacterial blooms for human health protection at regional and global scales.

Inactivation Kinetics of the Cyanobacterial Toxin Microcystin-LR by Free Chlorine

Worldwide, the increasing occurrence of toxins produced by cyanobacteria in water bodies used as source waters for drinking water has become an important public health issue. Microcystin-LR is one of the most commonly found cyanotoxins. A detailed evaluation of the free chlorine induced inactivation kinetics of extracellular microcystin-LR is presented in this study. Rate constants needed for chlorine inactivation of the toxin were derived from the data. The effects of varied pH, chlorine dose, toxin concentration, and temperature on the rate of inactivation were evaluated. Batch chlorination experiments were run using carbonate-buffered Milli-Q water at three different initial toxin concentrations (1, 2, and 8μg∕L), three different chlorine doses (1, 3, and 9mg∕L), and three different pH values (6.0, 7.5, and 9.0) at 11, 20 and 29°C. The study showed that extracellular microcystin-LR was inactivated by free chlorine and the inactivation rate was affected by pH. The highest inactivation rates were observed at pH 6.0 and the lowest at pH 9.0.

Microcystins (cyanobacteria hepatotoxins) bioaccumulation in fish and crustaceans from Sepetiba Bay (Brasil, RJ)

Blooms of cyanobacteria in water bodies cause serious environmental problems and the occurrence of toxic strains are also related with the human health. Aquatic animals could bioaccumulate microcystins (cyanobacteria hepatotoxins) and so, beyond water, the ingestion of contaminated food represents a human health risk. Recently, WHO recommended a maximum concentration of microcystins (MCYSTs) in drinking water and established the tolerable daily intake (TDI) for consumption of cyanobacteria products contends MCYSTs (0.04 μg −1 kg −1 day −1). Sepetiba Bay is located in the municipal districts of Rio de Janeiro, Mangaratiba and Itaguaı́ being an important place of fishing activity. Due to the industrial development in the area, this bay is submitted to different environmental impacts, increasing the organic and industrial pollution. A strain of the nanoplanktonic cyanobacteria Synechocystis aquatilis f. aquatilis that produce MCYSTs was already isolated. In this study, we verified MCYSTs presence in muscle tissue of fish and crustaceans, which were harvested monthly in Sepetiba Bay during 11 months, in order to evaluate the potential risk of their ingestion. MCYSTs were analyzed by immunoassay techniques using the ELISA Microcystin Plate Kit (ENVIROLOGIX INC ®) and the concentration were expressed as microcystin-LR equivalent. The analyses of seston samples, water, muscle tissues showed the presence of this cyanotoxin in all samples and it was verified that 19% of the animals' samples were above the limit recommended by WHO for human consumption. The maximum value found was of 103.3 μg kg −1 (TDI 0.52 μg kg −1 day −1) and the minimum, was 0.25 μg kg −1 in crabs muscle tissue (TDI of 0.001 μg kg −1 day −1). Such data demonstrate that, although in low concentrations, there is already a contamination of fish and crustaceans from Sepetiba Bay. We highlight that the recommended limit refers to healthy adult.

The control of cyanobacterial blooms by plant growth retardants (ancymidol, paclobutrazol, uniconazole)

The seasonal blooming of cyanobacteria in water bodies creates considerable medical and veterinary problems, because certain species are potential sources of toxins, principally neuro- and hepatotoxins. Much effort has been devoted to prevent them blooming. In this study, axenic cultures of Microcystis aeruginosa and Anabaena sp. were cultivated in medium Z supplemented with growth retardants. Cells were counted under a microscope each week for up to 8 weeks of culture. The growth retardants paclobutrazol, ancymidol and uniconazole greatly reduced the number of living cells, the effect already being striking after 24 hours of culture. Plant growth retardants can be effectively used in control of cyanobacterial blooms.