Microcystin Concentrations Research Articles

Morchella Effectively Removes Microcystins Produced by Microcystis aeruginosa.

Microcystins (MCs) produced by Microcystis aeruginosa are harmful to animal and human health, and there is currently no effective method for their removal. Therefore, the development of biological approaches that inhibit cyanobacteria and remove MCs is needed. We identified strain MB1, confirmed as Morchella, using morphological and mole-cular evolution methods. To assess the impact of strain MB1 on M. aeruginosa, we conducted an experiment in which we inoculated M. aeruginosa with Morchella strain MB1. After their co-cultivation for 4‍ ‍d, the inoculation with 0.9696‍ ‍g MB1 completely inhibited and removed M. aeruginosa while concurrently removing up to 95% of the MC content. Moreover, within 3‍ ‍d of their co-cultivation, MB1 removed more than 50% of nitrogen and phosphorus from the M. aeruginosa solution. Therefore, the development of effective biological techniques for MC removal is paramount in safeguarding both the environment and human well-being. We herein successfully isolated MB1 from its natural habitat. This strain effectively inhibited and removed M. aeruginosa and also reduced the content of nitrogen and phosphorus in the M. aeruginosa solution. Most importantly, it exhibited a robust capability to eliminate MCs. The present results offer a new method and technical reference for mitigating harmful algal blooms.

An assessment of a biosensor system for the quantification of microcystins in freshwater cyanobacterial blooms

Microcystin-producing cyanobacterial blooms are a global issue threatening drinking water supplies and recreation on lakes and beaches. Direct measurement of microcystins is the only way to ensure waters have concentrations below guideline concentrations; however, analyzing water for microcystins takes several hours to days to obtain data. We tested LightDeck Diagnostics’ bead beater cell lysis and two versions of the quantification system designed to give microcystin concentrations within 20 min and compared it to the standard freeze-thaw cycle lysis method and ELISA quantification. The bead beater lyser was only 30 % effective at extracting microcystins compared to freeze-thaw. When considering freeze-thaw samples analyzed in 2021, there was good agreement between ELISA and LightDeck version 2 (n = 152; R2 = 0.868), but the LightDeck slightly underestimated microcystins (slope of 0.862). However, we found poor relationships between LightDeck version 2 and ELISA in 2022 (n = 49, slopes 0.60 to 1.6; R2 < 0.6) and LightDeck version 1 (slope = 1.77 but also a high number of less than quantifiable concentrations). After the quantification issues are resolved, combining the LightDeck system with an already-proven rapid lysis method (such as microwaving) will allow beach managers and water treatment operators to make quicker, well-informed decisions.

Effects of Harmful Cyanobacteria on Drinking Water Source Quality and Ecosystems.

A seasonal plethora of cyanobacteria in the plankton community can have severe implications, not only for water ecosystems but also for the availability of treated water. The catchment of the Obrzyca River (a source of drinking water) is seasonally exposed to harmful cyanobacterial bloom. Previous studies (2008-2012; 2019) revealed that the most polluted water of the Obrzyca River was Uście, close to the outlet of Rudno Lake (at the sampling point). Therefore, the effect on this lake was specifically examined in this study. Sampling was performed from May to September at that site and from July to September 2020 at Rudno Lake. The conducted analysis revealed a massive growth of Aphanizomenon gracile, especially in Rudno Lake. The results showed not only the distinct impact of cyanobacterial bloom on phytoplankton biodiversity but also the presence of microcystins and other cyanopeptides in both sampling points. The maximal total concentration of microcystins (dmMC-RR, MC-RR, dmMC-LR, MC-LR, MC-LY, MC-YR) equaled 57.3 μg/L and the presence of cyanopeptides (aeruginosin, anabaenopeptin) was originally determined in Rudno Lake, August 2021. The presence of these toxins was highlighted in our results for the first time. The same samples from the lake were the most toxic in biotoxicological investigations using the planarian Dugesia tigrina. The performed bioassays proved that D. tigrina is a sensitive bioindicator for cyanotoxins. The physical and chemical indicators of water quality, i.e., color, temperature, total suspended solids, and total nitrogen and phosphorus, showed a significant correlation among each other and towards cyanobacterial abundance and microcystin concentrations.

Aerosolized Cyanobacterial Harmful Algal Bloom Toxins: Microcystin Congeners Quantified in the Atmosphere.

Cyanobacterial harmful algal blooms (cHABs) have the potential to adversely affect public health through the production of toxins such as microcystins, which consist of numerous molecularly distinct congeners. Microcystins have been observed in the atmosphere after emission from freshwater lakes, but little is known about the health effects of inhaling microcystins and the factors contributing to microcystin aerosolization. This study quantified total microcystin concentrations in water and aerosol samples collected around Grand Lake St. Marys (GLSM), Ohio. Microcystin concentrations in water samples collected on the same day ranged from 13 to 23 μg/L, dominated by the d-Asp3-MC-RR congener. In particulate matter <2.5 μm (PM2.5), microcystin concentrations up to 156 pg/m3 were detected; the microcystins were composed primarily of d-Asp3-MC-RR, with additional congeners (d-Asp3-MC-HtyR and d-Asp3-MC-LR) observed in a sample collected prior to a storm event. The PM size fraction containing the highest aerosolized MC concentration ranged from 0.44 to 2.5 μm. Analysis of total bacteria by qPCR targeting 16S rDNA revealed concentrations up to 9.4 × 104 gc/m3 in aerosol samples (≤3 μm), while a marker specific to cyanobacteria was not detected in any aerosol samples. Concentrations of aerosolized microcystins varied even when concentrations in water were relatively constant, demonstrating the importance of meteorological conditions (wind speed and direction) and aerosol generation mechanism(s) (wave breaking, spillway, and aeration systems) when evaluating inhalation exposure to microcystins and subsequent impacts on human health.

Microcystis genotypes in a tropical freshwater lake: Discovery of novel MIB-producing Microcystis with potentially unique synthesis pathway

Harmful algal blooms (HABs) are a threat to freshwater systems over the world due to the production of hepatotoxins like microcystin (MC), and nuisance taste and odour (T&O) compounds like 2-methylisoborneol (MIB). While MCs are known to cause detrimental effects to both water quality and human health, MIB is only reported to cause aesthetical problems. In this study, we investigated a tropical, urban lake that was experiencing persistent MC and MIB events. Although it was dominated by Microcystis blooms, analysis revealed that the toxigenic Microcystis were not the only species driving the MC concentrations. Additionally, there was also a lack of causative species for the MIB events. Through isolation, we have identified three toxigenic Microcystis found to produce four different variants of MCs, and two novel non-toxigenic Microcystis that were capable of producing MIB. The ability to produce MIB had never been previously reported for this species. Compared to other major producers such as Planktothricoides sp. and Streptomyces sp., the MIB synthase genes of our Microcystis sp. strains were partial, illustrating the possibility of unique synthesis pathways. The Microcystis sp. strains were found to produce about 2.77–5.22 fg MIB cell−1, with a majority of the contents (70–80 %) existing in the extracellular phase. Correlation analysis of field study indicated that phosphorus limitation may have an indirect effect on non-toxigenic Microcystis abundance and proportion by influencing the toxigenic genotype, suggesting that current measures to control HABs may favour the proliferation of the non-toxigenic Microcystis. The potential for Microcystis sp. to produce MIB through unique synthesis pathway, coupled with the potential dominance of non-toxigenic genotypes in Microcystis blooms, signals the possibility that non-toxigenic Microcystis should be monitored as well.

The prevalence and persistence of microcystin in seven subtropical reservoirs in China and associated potential risks for human health

Microcystins (MCs) are the most frequent cyanotoxins occurring in inland freshwaters, posing a serious threat to drinking water safety and human health. However, the distribution and risk of MCs in subtropical reservoirs in China are still unclear. In this study, we investigated the MCs pollution in seven subtropical reservoirs in Fujian Province, China. The results showed that most samples (87.74%) from all reservoirs were in a mesotrophic state during the survey period, and a variety of potential toxigenic cyanobacteria were detected, which resulted in the detection rate of MCs reaching 100%. The MCs concentration of surface samples ranged from 0.19 to 1.06 μg/L, and the proportion of MC-YR (43.72%) was the highest, followed by MC-RR (37.88%). The maximum was usually obtained in warmer seasons. The MCs concentration in stratified water samples ranged from 0.20 to 0.54 μg/L, while the MCs concentration in bottom water samples was sometimes higher than that in surface samples. MCs were positively correlated with most of the physicochemical parameters and the densities of phytoplankton phyla, but only negatively correlated with water depth, total nitrogen and nitrate nitrogen. MCs concentration was significantly positively correlated with the density of Microcystis and Cylindrospermopsis. Finally, risk assessments of MCs indicate that the risk from MCs pollution in all reservoirs studied remains low, particularly to humans. However, since the reservoir has different community compositions of toxin-producing cyanobacteria from that of shallow lakes, the long-term and regular monitoring and study of cyanotoxins should be strengthened in future under a changing climate.

Microcystin Concentrations, Partitioning, and Structural Composition during Active Growth and Decline: A Laboratory Study.

Microcystin can be present in variable concentrations, phases (dissolved and particulate), and structural forms (congeners), all which impact the toxicity and persistence of the algal metabolite. Conducting incubation experiments with six bloom assemblages collected from the Chowan River, North Carolina, we assessed microcystin dynamics during active growth and biomass degradation. Upon collection, average particulate and dissolved microcystin ranged between 0.2 and 993 µg L-1 and 0.5 and 3.6 µg L-1, respectively. The presence of congeners MC-LA, -LR, -RR, and -YR was confirmed with MC-RR and MC-LR being the most prevalent. Congener composition shifted over time and varied between dissolved and particulate phases. Particulate microcystin exponentially declined in five of six incubations with an average half-life of 10.2 ± 3.7 days, while dissolved microcystin remained detectable until the end of the incubation trials (up to 100 days). Our findings suggest that concerns about food-web transfer via intracellular toxins seem most warranted within the first few weeks of the bloom peak, while dissolved toxins linger for several months in the aftermath of the event. Also, it was indicated there were differences in congener profiles linked to the sampling method. We believe this study can inform monitoring strategies and aid microcystin-exposure risk assessments for cyanobacterial blooms.

Two duckweed species exhibit variable tolerance to microcystin-LR exposure across genotypic lineages

Cyanotoxins produced by harmful cyanobacteria blooms can damage freshwater ecosystems and threaten human health. Floating macrophytes may be used as a means of biocontrol by limiting light and resources available to cyanobacteria. However, genetic variation in macrophyte sensitivity to cyanotoxins could influence their suitability as biocontrol agents. We investigated the influence of such intraspecific variation on the response of two rapidly growing duckweed species, Lemna minor and Spirodela polyrhiza, often used in nutrient and metal bioremediation. We assessed two biomarkers related to productivity (biomass and chlorophyll A production) and two related to fitness measures (population size and growth rate). Fifteen genetic lineages of each species were grown in media containing common cyanotoxin microcystin-LR at ecologically relevant concentrations or control media for a period of twelve days. Genotype identity had a strong impact on all biomarker responses. Microcystin concentration slightly increased the final population sizes of both macrophyte species with a marginal effect on growth rate of L. minor and the chlorophyll A production of S. polyrhiza, but overall these species were very tolerant of microcystin. The strong tolerance supports the potential use of these plants as bioremediators of cyanobacterial blooms. However, differential impact of microcystin exposure discovered in single lineage models among genotypes indicates a potential for cyanotoxins to act as selective forces, necessitating attention to genotype selection for bioremediation.

Prediction of Water Level in Lakes by RNN-Based Deep Learning Algorithms to Preserve Sustainability in Changing Climate and Relationship to Microcystin

In recent years, intensive water use combined with global climate change has increased fluctuations in freshwater lake levels, hydrological characteristics, water quality, and water ecosystem balance. To provide a sustainable management plan in the long term, deep learning models (DL) can provide fast and reliable predictions of lake water levels (LWLs) in challenging future scenarios. In this study, artificial neural networks (ANNs) and four recurrent neural network (RNN) algorithms were investigated to predict LWLs that were applied in time series such as one day, five days, ten days, twenty days, one month, two months, and four months ahead. The results show that the performance of the Long Short-Term Memory (LSTM) model with a prediction of 60 days is in the very good range and outperforms the benchmark, the Naïve Method, by 78% and the ANN at the significance level (p &lt; 0.05) with an RMSE = 0.1762 compared to other DL algorithms. The RNN-based DL algorithms show better prediction performance, specifically, for long time horizons, 57.98% for 45 days, 78.55% for 60 days, and 58% for 120 days, and it is better to use a prediction period of at least 20 days with an 18.45% performance increase to take advantage of the gated RNN algorithms for predicting future water levels. Additionally, microcystin concentration was tightly correlated with temperature and was most elevated between 15 and 20 m water depths during the summer months. Evidence on LWL forecasting and microcystin concentrations in the context of climate change could help develop a sustainable water management plan and long-term policy for drinking water lakes.

Tracing the fate of microcystins from irrigation water to food chains: Studies with Fragaria vulgaris and Meriones shawi

Microcystins (MCs) are cyanobacterial toxins that can negatively impact human and animal health. This study investigated the bioaccumulation, transfer, depuration, and health risks of MCs in strawberry plants (Fragaria vulgaris) and Meriones shawi animals. The plants were irrigated with 1, 5, 10, and 20 μg/L MCs for 60 days (bioaccumulation phase) and then with clean water for 30 days (depuration phase). The harvested plants (roots and leaves) were then prepared in an aliquot form and used as feed for Meriones shawi. Liquid chromatography-mass spectrometry (LC/MS/MS) was used to measure MC concentrations in plant and animal tissues. The bioaccumulation of MCs was found to be highest in the roots, followed by leaves, fruits, liver, stomach, and fecal matter. The bioaccumulation factor (BAF) was highest in perlite (8.48), followed by roots (5.01), leaves (1.55), stomach (0.87), and fecal matter (1.18), indicating that the parts with high bioaccumulation factor had high translocation of MCs. The transfer of MCs to animal organs was low, and the daily toxin intake of adult consumers of strawberry fruit irrigated with 1, 5, 10, and 20 μg/L MC did not exceed the WHO-recommended limit of 0.04 μg MC-LR/Kg of bw/day. However, fruits from plants irrigated with 10 and 20 μg/L may pose a moderate health risk to children (25 Kg bw), and Meriones' consumption of leaves may pose a significant health risk. After the depuration phase, MC concentration in perlite, roots, leaves, and fruits decreased, indicating that depuration reduced the danger of MC transmission and bioaccumulation. The study also found that glutathione reductase and glutathione S-transferase activity were essential in the depuration of MCs in the tested plants. The findings suggest that legislation regulating the quality of irrigation water in terms of MC concentrations is necessary to prevent detrimental consequences to crops and human exposure.

Microcystin profiles in European noble crayfish Astacus astacus and water in Lake Steinsfjorden, Norway

Lake Steinsfjorden, an important noble crayfish (Astacus astacus) habitat, is often affected by blooms of Planktothrix spp. that produce microcystins (MCs). A poor correlation between MCs by ELISA in the water and in crayfish tissue in a study in 2015 prompted further investigation by LC–HRMS. LC–HRMS analyses of filters from water samples and on selected crayfish tissue extracts from the 2015 study revealed the presence of known and previously unreported MCs. Crayfish samples from May and June 2015 were dominated by MCs from the Planktothrix bloom, whereas in September novel MCs that appeared to be metabolites of MC-LR were dominant, even though neither these nor MC-LR were detected in the water in 2015. A water sample from October 2016 also showed MCs typical of Planktothrix (i.e., [d-Asp3]- and [d-Asp3,Dhb7]MC-RR and -LR), but low levels of MC-RR and MC-LR were detected in the lake water for the first time. In late summer and autumn, the MC profiles of crayfish were dominated by the homonorvaline (Hnv) variant MC-LHnv, a putative metabolite of MC-LR. Taken together, ELISA, LC–HRMS and previous PCR analyses showed that although Planktothrix was part of the crayfish diet, it was not the sole source of MCs in the crayfish. Possibly, crayfish in Lake Steinsfjorden may be ingesting MCs from benthic cyanobacteria or from contaminated prey. Therefore, information on the cyanobacterial or MC content in the water column cannot safely be used to make predictions about MC concentrations in the crayfish in Lake Steinsfjorden. Interestingly, the results also show that targeted LC–MS analysis of the crayfish would at times have underestimated their MC content by nearly an order of magnitude, even if all previously reported MC variants had been included in the analysis.

Concentration of total microcystins associates with nitrate and nitrite, and may disrupt the nitrogen cycle, in warm-monomictic lakes of the southcentral United States

Cyanobacterial blooms and the toxins they produce pose a growing threat worldwide. Mitigation of such events has primarily focused on phosphorus management and has largely neglected the role of nitrogen. Previous bloom research and proposed management strategies have primarily focused on temperate, dimictic lakes, and less on warm-monomictic systems like those at subtropical latitudes. The in-lake conditions, concentration of total microcystins, and microbial functioning of twenty warm-monomictic lakes in the southcentral United States were explored in the spring and summer of 2021. Our data revealed widespread microcystins in lakes across this region, some of which exceeded regulatory limits. Microcystins were higher in the spring compared to the summer, indicating that warm-monomictic lakes, even across a large range of precipitation, do not follow the trends of temperate dimictic lakes. Microcystins were found in surface waters and bottom waters well below the photic zone, reflecting the persistence of these toxins in the environment. Principal components analyses showed a strong association between microcystins, nitrate + nitrite, and Planktothrix relative abundance and transcriptional activity. Many systems exhibited stronger denitrification in the spring, perhaps contributing to the decreased toxin concentrations in the summer. Counter to most sampled lakes, one lake with the highest concentration of total microcystins indicated nitrogen cycle disruption, including inhibited denitrification. These findings are relevant to mitigating cyanobacterial blooms and toxin production in warm-monomictic systems, and suggests a need to consider nitrogen, and not solely phosphorus, in nutrient management discussions.

Changes in microcystin concentration in Lake Taihu, 13 years (2007–2020) after the 2007 drinking water crisis

Since the 2007 water crisis occurred in Lake Taihu, substantial measures have been taken to restore the lake. This study evaluates the effectiveness of these restoration activities. We examined the physicochemical parameters and the distribution of microcystin and Microcystis in both the water column and sediment during the bloom period of May 2020 to October 2020. The mean value of extracellular and intracellular microcystin content was 0.12 μg L−1 and 16.26 μg L−1, respectively. The mean value of microcystin in sediment was 172.02 ng g−1 and peaked in August. The concentration in the water and sediment was significantly lower than the historical average concentration. The abundance of toxigenic Microcystis and total Microcystis in the water column ranged from 2.61 × 102 to 2.25 × 109 copies·L−1 and 8.28 × 105 to 2.76 × 109 copies·L−1, respectively. The proportion of toxic Microcystis in the sediment ranging from 31.2% to 19.12%. The highest and lowest region was Meiliang Bay and Grass-algae type zone, respectively. The copy number of the 16S rRNA gene was 1–4 orders of magnitude higher than that of mcyA gene in populations of Microcystis, indicating that non-toxic Microcystis was the dominant form in the majority of the lake. The abundance of toxic Microcystis in the water column was positively correlated with total phosphorus, PO43--P and pH, while the water temperature played distinct role to the distribution of toxic Microcystis in sediment. Our research indicated phosphorus remains a key factor influencing the toxic Microcystis and microcystins in the water column. pH played distinct roles in the distribution of microcystins in sediment and water column. The increasing water temperature is a threat. Explicit management actions and policies, which take into account nutrient concentrations, pH, and increasing temperatures, are necessary to understand and control the distribution of microcystin and Microcystis in Lake Taihu.

RETRACTED] Short-term dynamics and growth parameters of cyanobacteria and microcystins in freshwater from the Sidi-Yacoub dam, North-east of Algeria

Abstract. Boudjellab ZE, Ghannam M, Chaib N, Chekroud Z. 2023. Short-term dynamics and growth parameters of cyanobacteria and microcystins in freshwater from the Sidi-Yacoub dam, North-east of Algeria. Biodiversitas 24: 5598-5609. The study aimed to establish the inventory of the blue-green algae species and monitoring the monthly evolution of their specific and total cell biovolume in Sidi-Yacoub dam, located northwest of Algeria from February 2021 to January 2022. At the same time, a monthly assessment of particulate and dissolved microcystin concentrations, chlorophyll pigment concentrations, and certain physicochemical parameters has been conducted. Eight species were listed, cited in descending order of their average relative abundance are: Microcystis aeruginosa (54.05%); Oscillatoria limosa (23.68%); Merismopedia sp. (8.34%); Anabaena cylindrica (3.53%); Aphanizomenon sp. (2.41%); Microcystis botrys (2.66%); Woronichinia sp. (2.95%) and Chroococcus limneticus (2.34%). The maximum value of the total biovolume, was recorded during December (27.4x106 µm3.L-1). The maximum concentration of chlorophyll-a and phycocyanin were respectively 55.26 and 47.46 µg L-1, recorded in September 2021. The microcystins detected where mainly in the cell-bound form, reaching a maximum concentration of 0.134 µg L-1 in October 2021. The principal component analysis shows a strong positive correlation between the total monthly cell biovolume, particulate microcystin (MCP) and some physicochemical parameters. M. aeruginosa has been identified as the primary producer of microcystins found in the eutrophic waters of the dam, with these microcystins being predominantly maintained in an intracellular form throughout most of the year.

Seasonal community dynamics and toxicity potential of cyanobacteria in Lough Arrow, an oligo-mesotrophic lake in the north-west of Ireland

Favourable water quality is paramount to ensuring the protection of natural habitats and the resources they provide. Phytoplankton are an important assessor of the health of aquatic ecosystems, particularly in lakes. As such, the characterisation of phytoplankton communities over time enables a detailed assessment of a water body’s ecological condition. This study examined the characteristics of cyanobacteria in Lough Arrow, a lake in Ireland’s northwest, over the course of a year to ascertain their community dynamics as well as potential for cyanotoxin production. DGGE analysis of 16 S rRNA gene amplicons for spherical cyanobacteria revealed seasonal shifts in Lough Arrow, with greater diversity in the summer and autumn. Non-metric multidimensional scaling showed that seasonal changes in the cyanobacterial community were largely driven by changes in environmental factors such as temperature and conductivity. The presence of the toxigenic species Microcystis sp. was confirmed from DGGE profiles. Analysis for the potential production of microcystin toxins in the lake was undertaken via qPCR analysis of the mcyE gene. No significant difference between the summer and autumn seasons was observed. Microcystin concentrations, estimated via the application of an ELISA assay, showed very low concentrations in the lake (max conc. 0.027 µg/l), which were not significantly different between the summer and autumn. The species richness and abundance of cyanobacteria in Lough Arrow was seasonal; responding dynamically to changes in environmental factors. The presence of Microcystis sp. and potential for microcystin production detected in the summer and autumn seasons indicating that the establishment of a tailored monitoring plan could be of benefit for better ascertaining and managing water quality parameters and potential risks to human and animal health.

Novel ecological implications of non-toxic Microcystis towards toxic ecotype in population-promoting toxic ecotype dominance at various N levels and cooperative defense against luteolin-stress.

Microcystin (MC)-producing (MC+) and MC-free (MC-) Microcystis always co-exist and interact during Microcystis-dominated cyanobacterial blooms (MCBs), where MC+Microcystis abundance and extracellular MC-content (EMC) determine the hazard extent of MCBs. The current study elucidated intraspecific interaction between MC+ and MC-Microcystis at various nitrogen (N) levels (0.5-50mg/L) and how such N-mediated interaction impacted algicidal and EMC-inhibiting effect of luteolin, a natural bioalgicide. Conclusively, MC+ and MC-Microcystis were inhibited mutually at N-limitation (0.5mg/L), which enhanced the algicidal and EMC-inhibiting effects of luteolin. However, at N-sufficiency (5-50mg/L), MC-Microcystis promoted MC+ ecotype growth and dominance, and such intraspecific interaction induced the cooperative defense of two ecotypes, weakening luteolin's algicidal and EMC-inhibiting effects. Mechanism analyses further revealed that MC+Microcystis in luteolin-stress co-culture secreted exopolymeric substances (EPSs) for self-protection against luteolin-stress and also released more EMC to induce EPS-production by MC-Microcystis as protectants, thus enhancing their luteolin-resistance and promoting their growth. This study provided novel ecological implications of MC-Microcystis toward MC+ ecotype in terms of assisting the dominant establishment of MC+Microcystis and cooperative defense with MC+ ecotype against luteolin, which guided the application of bioalgicide (i.e. luteolin) for MCBs and MCs pollution mitigation in different eutrophication-degree waters.

Toxic cyanobacteria induce coupled changes in gut microbiota and co-metabolite of freshwater gastropods

Frequent outbreaks of harmful cyanobacterial blooms and the microcystins (MCs) they produce seriously affect the survival of aquatic organisms. Interactions between gut microbiota and hosts often play crucial roles in driving the adaptation of aquatic organisms to environmental changes. In this study, we investigated the phenotypic indicators of the freshwater gastropod Bellamya aeruginosa, after uptake of Microcystis aeruginosa and explored its gut microbial composition and gut metabolites in response to toxic cyanobacterial stress. Results showed that the MCs concentration in the hepatopancreas of snails fed with toxic cyanobacteria decreased from 2.64 ± 0.14 μg·g−1 on day 7 to 1.16 ± 0.10 μg·g−1 on day 14. The compositions of the intestinal microbiota of snails fed with different algae significantly differed, and the relative abundance of gut microbes such as Lactobacillus and Sphingobium significantly increased after feeding toxic cyanobacteria. Significant differences also existed in intestinal metabolites, the relative abundance of the following metabolites significantly increased: l-proline, 5,6-DHET, stachyose, raffinose, and 3-isopropylmalate. Sankey network diagrams showing links between gut microbes and gut metabolites. The association of Lactobacillus and Sphingobium with amino acids may be related to host tolerance to toxicity, and the linkages of gut microbes with metabolites such as levan, imidazolepropionic acid, and eicosanoids may be associated with involvement in host immune responses. The association of microbes with stachyose and raffinose can help the host to regulate energy homeostasis. These results reveal the underlying mechanisms of gut microbes in the snail adaptation to toxic cyanobacterial stress. This study could be great important for gaining new insights into toxic cyanobacteria-induced changes in snail gut microbes and metabolites and their roles in snail adaptation to toxic cyanobacterial stress, and may provide important insights into the use of freshwater gastropods for the prevention and control of cyanobacterial blooms.

Geographic redistribution of microcystin hotspots in response to climate warming

High concentrations of cyanobacterial toxins such as microcystin represent a global challenge to water quality in lakes, threatening health, economies and ecosystem stability. Lakes are sentinels of climate change but how warming will affect microcystin concentrations is still unclear. Here we examine how warming impacts the probability of exceeding microcystin water quality thresholds across 2,804 lakes in the United States and show how future warming will alter these probabilities. We find that higher temperatures consistently increase the likelihood of microcystin occurrence but that the probability of microcystin concentrations above water quality thresholds is highest for water temperatures between 20 and 25 °C. Regions with temperatures that promote microcystin will shift to higher latitudes in the coming decades, leading to relative changes in exceedance probabilities of more than 50% in many basins of the United States. High nitrogen concentrations amplify the impact of rising temperatures, calling for increased awareness of a substantial hazard to ecosystems and human health under global warming.

Managing cyanobacteria with a water quality control curtain in Iron Gate Reservoir, California

Mejica BN, Ebert DA, Tanaka SK, Deas ML. 2023. Managing cyanobacteria with a water quality control curtain in Iron Gate Reservoir, California. Lake Reserv Manage. 39:291–310.Iron Gate Reservoir, a eutrophic monomictic reservoir on the Klamath River, a Pacific coast river within the United States, stratifies thermally during summer and is subject to cyanobacteria blooms that produce microcystin toxins, causing public health concerns. An impermeable curtain was installed in Iron Gate Reservoir upstream of the powerhouse intake to control the withdrawal depth and improve water quality of releases to the downstream Klamath River. Thermal stratification minimizes vertical downward movement of cyanobacteria-laden near-surface waters, and the curtain was hypothesized to reduce cyanobacteria and toxin concentrations downstream of the curtain and dam. The Wedderburn number, which indicates unstable (mixed) or stratified conditions, was used to calculate mixed layer depths and define conditions under which the curtain would be likely to be effective. Changes in chlorophyll a, cyanobacteria gene, Microcystis spp. gene, and microcystin concentrations were used to quantify curtain effectiveness for different curtain depths and mixed layer depths. When curtain depth extended below the mixed layer, concentrations of total chlorophyll a, total cyanobacteria, total Microcystis spp., and total microcystin in waters downstream of the curtain were statistically significantly reduced by an average of 87, 90, 78, and 64%, respectively. Concentrations were not consistently reduced downstream of the curtain under other configurations. Findings indicate the curtain can be managed to take advantage of stratification within the epilimnion and address issues pertaining to downstream cyanobacteria and associated toxins, and should improve water quality and reduce public health notices for the 305.7 km of river downstream of Iron Gate Dam.

Effects of Algicidal Macrophyte Metabolites on Cyanobacteria, Microcystins, Other Plankton, and Fish in Microcosms.

To control harmful algae blooms (HABs), methods based on natural mechanisms are now required. We investigated the effects of an algicide derived from macrophyte metabolites, namely mixtures of gallic, tetradecanoic, heptanoic, and octanoic acids (1:1:1:1 mass ratio, a total concentration of 14 mg/L), on the biomass of cyanobacteria and other plankton and the production of microcystins under experimental conditions. Two types of microcosms have been created: simple (microalgae, cyanobacteria, and zooplankton) and complex (microalgae, cyanobacteria, zooplankton, and planktivorous fish). We observed the dynamics of the phytoplankton structure, the concentrations of microcystins and chlorophyll-a, hydrochemistry, and the status of zooplankton and fish in both types of microcosms with and without algicide for one month (from 19 July to 19 August 2021). The introduction of algicide caused changes in phytoplankton structure, a drop in cyanobacterial biomass, and a decrease in the total concentration of microcystins. Surprisingly, the contributions of the most toxic microcystins (LR form) were higher in both types of microcosms exposed to algicide than in microcosms without algicide. The inhibitory effect on the cyanobacterial biomass was most significant in complex ecosystems (containing fish), while it was only observed at the end of the exposure in simple ecosystems. Not only algicide but also phytoplankton consumed by fish and zooplankton, as well as nutrient excretory activity by both consumers, seem to have impact on cyanobacterial biomass. This study found that the using chemical substances similar to macrophyte metabolites can help regulate HABs and cyanotoxins. However, the results differ depending on ecosystem type.