Cyanobacterial Toxin Microcystin Research Articles

Toxins from harmful algal blooms: How copper and iron render chalkophore a predictor of microcystin production

Research on harmful algal blooms has focused on macronutrients, yet recent research increasingly indicates that understanding micronutrient roles is also important in the development of effective environmental management interventions. Here, we report results on metallophore production from mesocosms amended with copper and iron (enzymatic co-factors in photosynthetic electron transport) to probe questions of how cyanobacteria navigate the divide between copper nutrition, copper toxicity, and issues with iron bioavailability. These experiments utilized Microcystis, Chlorella and Desmodesmus spp., in mono- and mixed-cultures in lake water from a large, hypereutrophic lake (Taihu, China). To initiate experiments, copper and iron amendments were added to mesocosms containing algae that had been acclimated to achieve a state of copper and iron limitation. Mesocosms were analyzed over time for a range of analytes including algal growth parameters, algal assemblage progression, copper/iron concentrations and biomolecule production of chalkophore, siderophore and total microcystins. Community Trajectory Analysis and other multivariate methods were used for analysis resulting in our findings: 1) Microcystis spp. manage copper/iron requirements though a dynamically phased behavior of chalkophore/siderophore production according to their copper and iron limitation status (chalkophore correlates with Cu concentration, R2 = 0.99, and siderophore correlates with the sum of Cu and Fe concentrations, R2 = 0.98). 2) A strong correlation was observed between the production of chalkophore and the cyanobacterial toxin microcystin (R2 = 0.76)—Chalkophore is a predictor of microcystin production. 3) Based on our results and literature, we posit that Microcystis spp. produces microcystin in response to copper/iron availability to manage photosystem productivity and effect an energy-saving status. Results from this work underscore the importance of micronutrients in influencing harmful algal bloom progression and represents a major advance in understanding the ecological function for the cyanobacterial toxin microcystin as a hallmark of micronutrient limitation stress.

Cyanobacterial Harmful Algal Bloom Toxin Microcystin and Increased Vibrio Occurrence as Climate-Change-Induced Biological Co-Stressors: Exposure and Disease Outcomes via Their Interaction with Gut-Liver-Brain Axis.

The effects of global warming are not limited to rising global temperatures and have set in motion a complex chain of events contributing to climate change. A consequence of global warming and the resultant climate change is the rise in cyanobacterial harmful algal blooms (cyano-HABs) across the world, which pose a threat to public health, aquatic biodiversity, and the livelihood of communities that depend on these water systems, such as farmers and fishers. An increase in cyano-HABs and their intensity is associated with an increase in the leakage of cyanotoxins. Microcystins (MCs) are hepatotoxins produced by some cyanobacterial species, and their organ toxicology has been extensively studied. Recent mouse studies suggest that MCs can induce gut resistome changes. Opportunistic pathogens such as Vibrios are abundantly found in the same habitat as phytoplankton, such as cyanobacteria. Further, MCs can complicate human disorders such as heat stress, cardiovascular diseases, type II diabetes, and non-alcoholic fatty liver disease. Firstly, this review describes how climate change mediates the rise in cyanobacterial harmful algal blooms in freshwater, causing increased levels of MCs. In the later sections, we aim to untangle the ways in which MCs can impact various public health concerns, either solely or in combination with other factors resulting from climate change. In conclusion, this review helps researchers understand the multiple challenges brought forth by a changing climate and the complex relationships between microcystin, Vibrios, and various environmental factors and their effect on human health and disease.

A Feasibility Study into the Production of a Mussel Matrix Reference Material for the Cyanobacterial Toxins Microcystins and Nodularins.

Microcystins and nodularins, produced naturally by certain species of cyanobacteria, have been found to accumulate in aquatic foodstuffs such as fish and shellfish, resulting in a risk to the health of the seafood consumer. Monitoring of toxins in such organisms for risk management purposes requires the availability of certified matrix reference materials to aid method development, validation and routine quality assurance. This study consequently targeted the preparation of a mussel tissue reference material incurred with a range of microcystin analogues and nodularins. Nine targeted analogues were incorporated into the material as confirmed through liquid chromatography with tandem mass spectrometry (LC-MS/MS), with an additional 15 analogues detected using LC coupled to non-targeted high resolution mass spectrometry (LC-HRMS). Toxins in the reference material and additional source tissues were quantified using LC-MS/MS, two different enzyme-linked immunosorbent assay (ELISA) methods and with an oxidative-cleavage method quantifying 3-methoxy-2-methyl-4-phenylbutyric acid (MMPB). Correlations between the concentrations quantified using the different methods were variable, likely relating to differences in assay cross-reactivities and differences in the abilities of each method to detect bound toxins. A consensus concentration of total soluble toxins determined from the four independent test methods was 2425 ± 575 µg/kg wet weight. A mean 43 ± 9% of bound toxins were present in addition to the freely extractable soluble form (57 ± 9%). The reference material produced was homogenous and stable when stored in the freezer for six months without any post-production stabilization applied. Consequently, a cyanotoxin shellfish reference material has been produced which demonstrates the feasibility of developing certified seafood matrix reference materials for a large range of cyanotoxins and could provide a valuable future resource for cyanotoxin risk monitoring, management and mitigation.

Chlorophyll a as an indicator of microcystin: Short-term forecasting and risk assessment in Lake Erie

We developed a Bayesian hierarchical modeling framework to establish a short-term forecasting model of particulate cyanobacterial toxin concentrations in Western Lake Erie using chlorophyll a concentration as the predictor. The model evolves over time with additional data to reflect the changing dynamics of cyanobacterial toxin production. Specifically, parameters of the empirical relationship between the cyanobacterial toxin microcystin and chlorophyll a concentrations are allowed to vary annually and seasonally under a hierarchical framework. As such, the model updated using the most recent sampling data is suited to provide short-term forecasts. The reduced model predictive uncertainty makes the model a viable tool for risk assessment. Using data from the long-term Western Lake Erie harmful algal bloom monitoring program (2008–2018), we illustrate the model-building and model-updating process and the application of the model for short-term risk assessment. The modeling process demonstrates the use of the Bayesian hierarchical modeling framework for developing informative priors in Bayesian modeling.

Predicting microcystin occurrence in freshwater lakes and reservoirs: assessing environmental variables

ABSTRACT Determining the environmental conditions that influence the occurrence and concentration of the cyanobacterial toxin microcystin (MC) is a critical step for predicting cases in which the toxin will adversely affect drinking water sources, recreational waterbodies, and other freshwater ecosystems. Although widely studied, little consensus exists regarding the factors that influence MC on a global scale. The objective of this study was to identify the environmental variables most strongly associated with MC concentrations using observational data from lakes and reservoirs around the world while also addressing the substantial proportions of missing values that a large aggregated dataset often involves. A total of 124 studies containing data from an estimated 2040 lakes and reservoirs in 22 countries was used to construct a global dataset. Variables including <35% of non-missing observations were removed prior to analysis. Missing values for the remaining 12 predictors of MC were imputed using an iterative imputation algorithm based on a random forest approach. Variable selection was performed with generalized additive modeling on the complete case and imputed datasets. Models applied to the imputed data produced lower prediction errors than those fit to the complete dataset. Variables of greatest significance to MC concentration included location (longitude–latitude pairs), total nitrogen, turbidity, and pH. Total phosphorus was not found to be a strong predictor of MC. In addition to assisting water resource managers in protecting their waterbodies against MC, the presented methodologies may provide a useful framework for future water quality modeling while accounting for varying proportions of missing data.

Toxins and Other Bioactive Metabolites in Deep Chlorophyll Layers Containing the Cyanobacteria Planktothrix cf. isothrix in Two Georgian Bay Embayments, Lake Huron.

The understanding of deep chlorophyll layers (DCLs) in the Great Lakes—largely reported as a mix of picoplankton and mixotrophic nanoflagellates—is predominantly based on studies of deep (>30 m), offshore locations. Here, we document and characterize nearshore DCLs from two meso-oligotrophic embayments, Twelve Mile Bay (TMB) and South Bay (SB), along eastern Georgian Bay, Lake Huron (Ontario, Canada) in 2014, 2015, and 2018. Both embayments showed the annual formation of DCLs, present as dense, thin, metalimnetic plates dominated by the large, potentially toxic, and bloom-forming cyanobacteria Planktothrix cf. isothrix. The contribution of P. cf. isothrix to the deep-living total biomass (TB) increased as thermal stratification progressed over the ice-free season, reaching 40% in TMB (0.6 mg/L at 9.5 m) and 65% in South Bay (3.5 mg/L at 7.5 m) in 2015. The euphotic zone in each embayment extended down past the mixed layer, into the nutrient-enriched hypoxic hypolimnia, consistent with other studies of similar systems with DCLs. The co-occurrence of the metal-oxidizing bacteria Leptothrix spp. and bactivorous flagellates within the metalimnetic DCLs suggests that the microbial loop plays an important role in recycling nutrients within these layers, particularly phosphate (PO4) and iron (Fe). Samples taken through the water column in both embayments showed measurable concentrations of the cyanobacterial toxins microcystins (max. 0.4 µg/L) and the other bioactive metabolites anabaenopeptins (max. ~7 µg/L) and cyanopeptolins (max. 1 ng/L), along with the corresponding genes (max. in 2018). These oligopeptides are known to act as metabolic inhibitors (e.g., in chemical defence against grazers, parasites) and allow a competitive advantage. In TMB, the 2018 peaks in these oligopeptides and genes coincided with the P. cf. isothrix DCLs, suggesting this species as the main source. Our data indicate that intersecting physicochemical gradients of light and nutrient-enriched hypoxic hypolimnia are key factors in supporting DCLs in TMB and SB. Microbial activity and allelopathy may also influence DCL community structure and function, and require further investigation, particularly related to the dominance of potentially toxigenic species such as P. cf. isothrix.

Next-generation sequencing of DNA from resting eggs: signatures of eutrophication in a lake’s sediment

Hatching resting stages of ecologically important organisms such as Daphnia from lake sediments, referred to as resurrection ecology, is a powerful approach to assess changes in alleles and traits over time. However, the utility of the approach is constrained by a few obstacles, including low and/or biased hatching among genotypes. Here, we eliminated such bottlenecks by investigating DNA sequences isolated directly (i.e. without hatching) from resting eggs found in the sediments of Lake Constance spanning pre-, peri-, and post-eutrophication. While we expected genome-wide changes, we specifically expected changes in alleles related to pathways involved in mitigating effects of cyanobacterial toxins. We used pairwise FST-analyses to identify transcripts that showed strongest divergence among the four different populations and a clustering analysis to identify correlations between allele frequency shifts and changes in abiotic and biotic lake parameters. In a cluster that correlated with the increased abundance of cyanobacteria in Lake Constance we find genes that have been reported earlier to be differentially expressed in response to the cyanobacterial toxin microcystin and to microcystin-free cyanobacteria. We further reveal the enrichment of gene ontology terms that have been shown to be involved in microcystin-related responses in other organisms but not yet in Daphnia and as such are candidate loci for adaptation of natural Daphnia populations to increased cyanobacterial abundances. In conclusion this approach of investigating DNA extracted from Daphnia resting stages allowed to determine frequency changes of loci in a natural population over time.

Using syndromic surveillance to monitor response to cyanotoxin contamination event

ObjectiveExamine healthcare seeking behavior in a population exposed to low levels of cyanotoxins in the public drinking water supplyand quantify how publicity of the event may have affected perceptions of risk in the affected population.IntroductionCyanotoxins are unregulated, emerging contaminants that have been associated with adverse health effects, including gastroenteritis, when consumed at high levels1,2. In May and June of 2018 cyanotoxins were detected in the public drinking water system for Salem, OR at levels above Environmental Protection Agency (EPA) health advisory levels for sensitive groups3. Sensitive groups were defined as children under 6, elderly adults, pregnant women, nursing mothers, people with compromised immune systems, people receiving dialysis, people with pre-existing liver conditions, and pets. Several health advisories were issued, and there was substantial media coverage of the event. The Oregon Health Authority (OHA) organized an Incident Management Team (IMT), which coordinated activities with other state and local agencies. Oregon ESSENCE staff used syndromic surveillance to monitor the population for health effects and healthcare seeking behavior.MethodsOregon ESSENCE staff developed syndromic surveillance queries to monitor visits made to local emergency departments (i.e., visits by hospital location), as well as visits made by residents of the affected area (i.e., visits by patient location). Specifically, Oregon ESSENCE staff monitored total visits, gastroenteritis syndrome, visits by age group, and mentions of the word ‘water’ daily during the relevant time period. OHA communications staff tracked media coverage of the event. After the event, Oregon ESSENCE staff reconciled syndromic surveillance visit data with water test data, health advisory status, and media coverage to characterize how messaging may have affected healthcare seeking behavior.ResultsCyanotoxins were detected at levels above EPA guidelines for sensitive groups on 9 days between May 23, 2018 and June 19, 2019. OHA identified 67 news articles related to the event published in May and 179 published in June. Additionally, there was an unquantified amount of activity on social media, and a mass text alert that was sent out by the Oregon Office of Emergency Management. Visits for gastroenteritis were highest on the days immediately following the issuance of the first drinking water advisory. The first drinking water advisory was issued three days after the first results that contained cyanotoxins at levels exceeding the EPA guidelines for sensitive groups were received. Visits where the word ‘water’ was mentioned were similarly elevated immediately after the first drinking water advisory was issued. However, visits for gastroenteritis were also above expected levels on one day that had a water sample above EPA guidelines for sensitive groups, but before the first drinking water advisory was issued.ConclusionsBecause cyanotoxins are unregulated, limited federal guidance was available and it took several days for the Oregon Health Authority to develop state guidance and educational materials. This delay contributed to public confusion about the level of risk associated with drinking the water, as well as confusion about which groups of people should avoid drinking the water. Our data suggest that emergency department visit behavior was largely driven by publicity of the event. Visits to the emergency department for gastroenteritis and mentions of the word ‘water’ decreased as more public information and guidance became available. However, we cannot rule out a real health effect related to cyanotoxins in the drinking water for area residents. One lesson learned from this type of high profile event relates to tracking of media coverage; it is difficult to measure how many people media coverage actually reaches, and attempting to characterize media coverage becomes more difficult after the event.ReferencesU.S. EPA (United States Environmental Protection Agency). 2015. Drinking Water Health Advisory for the Cyanobacterial Toxin Cylindrospermopsin. EPA 820R15101, Washington, DC; June, 2015. Available from: http://water.epa.gov/drink/standards/hascience.cfmU.S. EPA (United States Environmental Protection Agency). 2015. Drinking Water Health Advisory for the Cyanobacterial Toxin Microcystin. EPA 820R15100, Washington, DC; June, 2015. Available from: http://water.epa.gov/drink/standards/hascience.cfmU.S. EPA (United States Environmental Protection Agency). 2015. 2015 Drinking Water Health Advisories for Two Cyanobacterial Toxins. EPA 820F15003, Washington, DC; June, 2015. Available from: https://www.epa.gov/sites/production/files/2017-06/documents/cyanotoxins-fact_sheet-2015.pdf

Application of passive sampling for sensitive time-integrative monitoring of cyanobacterial toxins microcystins in drinking water treatment plants

Calibrated adsorption-based passive samplers were used for time-integrative monitoring of microcystins (MCs) in three full-scale drinking water treatment plants (DWTPs) in the Czech Republic during two vegetation seasons (Jun–Nov), in parallel with traditional discrete sampling. MCs were detected in epilimnetic water samples at concentrations up to 14 μg/L, but their levels in raw water in DWTPs were below 1 μg/L WHO guideline value for drinking water. Conventional treatment technologies (coagulation/filtration) eliminated cyanobacteria and intracellular toxins but had a limited removal efficiency for extracellular toxins. MCs were regularly detected in final treated water, especially in DWTPs equipped only with the conventional treatment, but their concentrations were below the quantitation limit of discrete sampling (<25 ng/L). Passive samplers in combination with LC-MS/MS analysis provided excellent sensitivity allowing to detect time-weighted average (TWA) concentrations of MCs as low as 20–200 pg/L after 14-d deployment. Median MC TWA concentrations in the treated water from the individual DWTPs were 1–12 ng/L, and most likely did not present significant health risks. Passive samplers well reflected spatiotemporal variations of MCs, actual concentrations of extracellular toxins, MC removal efficiency in DWTPs, and toxin concentrations in the treated water. Passive sampling can be effectively used for assessment and management of MC health risks during DWTP operation.

PARP1 Is Up-Regulated in Non-small Cell Lung Cancer Tissues in the Presence of the Cyanobacterial Toxin Microcystin.

Non-small cell lung cancer (NSCLC) is the major form of lung cancer, with adenocarcinoma (LUAD) and squamous cell carcinoma (LUSC) being its major subtypes. Smoking alone cannot completely explain the lung cancer etiology. We hypothesize that altered lung microbiome and chronic inflammatory insults in lung tissues contribute to carcinogenesis. Here we explore the microbiome composition of LUAD samples, compared to LUSC and normal samples. Extraction of microbiome DNA in formalin-fixed, paraffin-embedded (FFPE) lung tumor and normal adjacent tissues was meticulously performed. The 16S rRNA product from extracted microbiota was subjected to microbiome amplicon sequencing. To assess the contribution of the host genome, CD36 expression levels were analyzed then integrated with altered NSCLC subtype-specific microbe sequence data. Surprisingly phylum Cyanobacteria was consistently observed in LUAD samples. Across the NSCLC subtypes, differential abundance across four phyla (Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes) was identified based on the univariate analysis (p-value < 6.4e-4 to 3.2e-2). In silico metagenomic and pathway analyses show that presence of microcystin correlates with reduced CD36 and increased PARP1 levels. This was confirmed in microcystin challenged NSCLC (A427) cell lines and Cyanobacteria positive LUAD tissues. Controlling the influx of Cyanobacteria-like particles or microcystin and the inhibition of PARP1 can provide a potential targeted therapy and prevention of inflammation-associated lung carcinogenesis.

Histopathological and biochemical effects of cyanobacterial cells containing microcystin‐LR on Tilapia fish

AbstractBlooms of Microcystis aeruginosa, commonly observed in many lakes of Tamil Nadu, produce the cyanobacterial toxin Microcystin, which has tumor promoting property in fish. Strains of Microcystis aeruginosa species have the same morphology but may vary in their toxicity. In the present study, Microcystin produced by Microcystis aeruginosa from Thenneri lake in Kancheepuram district of Tamil Nadu, was isolated and characterized by high‐performance liquid chromatography and electron spray ionization mass spectroscopy. Based on spectroscopic results the toxin was identified as Microcystin‐LR. Toxicogenicity was evident from the alteration in the activity of antioxidant enzymes [Glutathione S‐transferase and Catalase] and increase of protein and lipid peroxidation contents in Oreochromis niloticus, a fresh water fish species, after controlled exposure to Microcystis aeruginosa cells. Toxicity was further confirmed by histopathological changes in gill, liver and intestine of exposed fish.

Changes in muscle biochemistry, myoglobin and cytoglobin in goldfishCarassius auratusexposed to hypoxia-reoxygenation and microcystin RR

AbstractCyanobacterial toxins and oxygen depletion pose serious challenges to aquatic organisms. In this study, the goldfish Carassius auratus was exposed to hypoxia-reoxygenation episodes as well as a cyanobacterial toxin microcystin arginine arginine (MCRR) with an aim of assessing the toxicity of the stressors to muscle biochemistry, cytoglobin mRNA and myoglobin mRNA. The result showed that MCRR and hypoxia-reoxygenation synergistically reduced the total antioxidant capacity of the muscle by over 90%; glutathione peroxidase activity was also significantly reduced in the groups exposed to MCRR and hypoxia (p < 0.05). Sodium ATPase (Na-ATPase) and total ATPase (tATPase) varied from 14.68 ± 2.2 to 27.87 ± 2.0 U/mg protein and were significantly reduced by MCRR (p < 0.005) only. Glucose and protein (sources of energy) were elevated in the muscles of goldfish exposed to MCRR, especially during reoxygenation, although only the latter was significant. Myoglobin and cytoglobin mRNA were not significantly infl...

Response surface modeling and optimization of microcystin-LR removal from aqueous phase by polyacrylamide/sodium alginate–montmorillonite superabsorbent nanocomposite

AbstractThe adsorptive removal of the most commonly occurring cyanobacterial toxin microcystin–LR by polyacrylamide/sodium alginate-modified montmorillonite (PAM/SA-MMT) superabsorbent nanocomposite was investigated through the HPLC/UV system. The process of PAM/SA-MMT preparation and MC-LR adsorption was characterized by scanning electron microscopy, energy dispersive X-ray microanalysis, X-ray diffraction analysis, and Fourier transform infrared spectroscopy analysis. With the application of Box–Behnken statistical experimental design combined with Response surface methodology, the quadratic statistical model was established to predict the interactive effects of pH, weight ratio (wr) of AM to SA, and weight content (wt) of MMT on MC-LR adsorption and to optimize the main controlling parameters. The maximum adsorption capacity was observed with pH 2.5–4.5, wr 55–65, and wt3–5%. The MC-LR adsorption capacity of PAM/SA-MMT increased with increase in temperature from 10 to 40°C. Kinetics were consistent wit...

Fluctuations in microcystin concentrations, potentially toxic Microcystis and genotype diversity in a cyanobacterial community from a tropical reservoir

In the study of cyanobacterial communities, molecular methods can be used to detect and quantify toxin-producing strains and assess genotype diversity. These are promising methods for estimating the risk of exposure to the cyanobacterial toxin microcystin (MC), assuming that the abundance of toxic genotypes is related to the MC concentration. This assumption has been tested in many studies, most of which were conducted in temperate and subtropical aquatic environments, and has not always been met. In this study, we collected cyanobacterial samples from a tropical reservoir and tested whether the MC concentration could be explained by variations in the number or ratio of toxin-producing genotypes or by the presence of certain Microcystis genotypes. The genetic diversity of cyanobacteria was determined by cpcBA sequencing, and the proportion of potential MC-producing genotypes was quantified by qPCR using mcyB as the target gene. Cyanobacteria dominated during the entire sampling period (88.4–99.8% of the total phytoplankton biomass), with Microcystis, Anabaena and Cylindrospermopsis occurring as the main genera. Three major Microcystis genotypes were recognized along with other rare or unique genotypes. MCs were detected in all samples (MC-LR, RR and YR), with most concentrations being less than 200ngL−1. Microcystis was the most abundant group during all the study period and was the main MC-producing genus. Potentially toxic Microcystis cells were present in all samples, varying from 10% to 100% of the total Microcystis. MC concentrations were not correlated with the number or ratio of toxic cells of Microcystis determined by qPCR or with the predominance of certain genotypes. These results indicate the limitations of using molecular methods such as qPCR in MC risk assessment.

Bioreactor study employing bacteria with enhanced activity toward cyanobacterial toxins microcystins.

An important aim of white (grey) biotechnology is bioremediation, where microbes are employed to remove unwanted chemicals. Microcystins (MCs) and other cyanobacterial toxins are not industrial or agricultural pollutants; however, their occurrence as a consequence of human activity and water reservoir eutrophication is regarded as anthropogenic. Microbial degradation of microcystins is suggested as an alternative to chemical and physical methods of their elimination. This paper describes a possible technique of the practical application of the biodegradation process. The idea relies on the utilization of bacteria with a significantly enhanced MC-degradation ability (in comparison with wild strains). The cells of an Escherichia coli laboratory strain expressing microcystinase (MlrA) responsible for the detoxification of MCs were immobilized in alginate beads. The degradation potency of the tested bioreactors was monitored by HPLC detection of linear microcystin LR (MC-LR) as the MlrA degradation product. An open system based on a column filled with alginate-entrapped cells was shown to operate more efficiently than a closed system (alginate beads shaken in a glass container). The maximal degradation rate calculated per one liter of carrier was 219.9 µg h−1 of degraded MC-LR. A comparison of the efficiency of the described system with other biological and chemo-physical proposals suggests that this new idea presents several advantages and is worth investigating in future studies.

Summary of microcystin concentrations in Minnesota lakes

Minnesota has compiled a fairly extensive database on the cyanobacterial toxin microcystin (MC). These data have been acquired through targeted lake studies, incident-based investigations, and stratified random surveys as a part of the US EPA's 2007 and 2012 National Lakes Assessments. This paper updates previous efforts and provides a statistical summary of all Minnesota MC data collected by the Minnesota Pollution Control Agency from 2004 to 2012. These data provide a basis for (1) describing the influence sampling regimes have on reported MC values, (2) describing regional patterns in MC across 3 distinct Minnesota ecoregions, and (3) describing the relative risk of encountering elevated MC with respect to sampling regimes. This summary places MC concentrations in perspective for Minnesota and also provides a comparative database, which other entities that collect MC may use to place their results in perspective.

Influences of Cyanobacterial Toxins Microcystins on the Seedling of Plants

Cyanobacterial blooms associated by their toxins have been increasing in frequency in fresh water bodies throughout the world. Among the cyanobacterial toxins, microcystins (MC) are the most common and cause severe adverse impacts on plants, aquatic organisms and human beings. In this study, the effects of MC (at the concentrations of 20 and 200 μg·L-1) from field water and crude extract of cyanobacterial scum (mainly Microcystis spp.) from the Dau Tieng Reservoir, Vietnam, on the seedlings of three plants, Brassica rapa-chinensis, B. narinosa and Nasturtium officinale, were investigated for over a period of 7 days. The results showed that MC reduced the fresh weight, root and shoot length of the exposed seedlings. In addition, abnormalities of leaf shape and color of B. rapa-chinensis under exposure to MC were observed. The results implied that MC were taken up and might be accumulated in the seedlings possessing potential risk to consumers as seedlings of these plants are a common food source for Vietnamese. To the best of our knowledge, this is the first report on the effects of MC on B. rapa-chinensis, B. narinosa and N. officinale.

Potent toxins in Arctic environments – Presence of saxitoxins and an unusual microcystin variant in Arctic freshwater ecosystems

Cyanobacteria are the predominant phototrophs in freshwater ecosystems of the polar regions where they commonly form extensive benthic mats. Despite their major biological role in these ecosystems, little attention has been paid to their physiology and biochemistry. An important feature of cyanobacteria from the temperate and tropical regions is the production of a large variety of toxic secondary metabolites. In Antarctica, and more recently in the Arctic, the cyanobacterial toxins microcystin and nodularin (Antarctic only) have been detected in freshwater microbial mats. To date other cyanobacterial toxins have not been reported from these locations. Five Arctic cyanobacterial communities were screened for saxitoxin, another common cyanobacterial toxin, and microcystins using immunological, spectroscopic and molecular methods. Saxitoxin was detected for the first time in cyanobacteria from the Arctic. In addition, an unusual microcystin variant was identified using liquid chromatography–mass spectrometry. Gene expression analyses confirmed the analytical findings, whereby parts of the sxt and mcy operon involved in saxitoxin and microcystin synthesis, were detected and sequenced in one and five of the Arctic cyanobacterial samples, respectively. The detection of these compounds in the cryosphere improves the understanding of the biogeography and distribution of toxic cyanobacteria globally. The sequences of sxt and mcy genes provided from this habitat for the first time may help to clarify the evolutionary origin of toxin production in cyanobacteria.

High microcystin concentrations occur only at low nitrogen-to-phosphorus ratios in nutrient-rich Canadian lakes

Although the cyanobacterial toxin microcystin has been detected in Canadian fresh waters, little is known about its prevalence on a national scale. Here, we report for the first time on microcystin in 246 water bodies across Canada based on 3474 analyses. Over the last 10 years, microcystins were detected in every province, often exceeding maximum guidelines for potable and recreational water quality. Microcystins were virtually absent from unproductive systems and were increasingly common in nutrient-rich waters. The probable risk of microcystin concentrations exceeding water quality guidelines was greatest when the ratio of nitrogen (N) to phosphorus (P) was low and rapidly decreased at higher N:P ratios. Maximum concentrations of microcystins occurred in hypereutrophic lakes at mass ratios of N:P below 23. Our models may prove to be useful screening tools for identifying potentially toxic “hotspots” or “hot times” of unacceptable microcystin levels. A future scientific challenge will be to determine whether there is any causal link between N:P ratios and microcystin concentrations, as this may have important implications for the management of eutrophied lakes and reservoirs.

Enzymatic pathway for biodegrading microcystin LR in Sphingopyxis sp. C-1

The mlr gene cluster consisting of mlrA, mlrB, mlrC, and mlrD is involved in the degradation of the cyanobacterial toxin microcystin. However, it is unclear which degradation intermediates are metabolized by MlrB and MlrC. To address these questions, we constructed recombinant Escherichia coli to overproduce MlrB and MlrC from Sphingopyxis sp. C-1, and determined which intermediates were degraded in cell-free extracts. The cell-free extract containing MlrB degraded linearized microcystin-LR, giving rise to a tetrapeptide. The cell-free extract of MlrC degraded linearized microcystin-LR and also degraded the tetrapeptide to the amino acid Adda. These results indicate that linearized microcystin-LR is degraded by both MlrB and MlrC, and tetrapeptide is degraded by specifically by MlrC in Sphingopyxis sp. C-1.