Metagenomic insights into jellyfish-associated microbiome dynamics during strobilation.

Host-associated microbiomes can play key roles in the metamorphosis of animals. Most scyphozoan jellyfish undergo strobilation in their life cycles, similar to metamorphosis in classic bilaterians. The exploration of jellyfish microbiomes may elucidate the ancestral mechanisms and evolutionary trajectories of metazoan-microbe associations and interactions during metamorphosis. However, current knowledge of the functional features of jellyfish microbiomes remains limited. Here, we performed a genome-centric analysis of associated microbiota across four successive life stages (polyp, early strobila, advanced strobila, and ephyra) during strobilation in the common jellyfish Aurelia coerulea. We observed shifts in taxonomic and functional diversity of microbiomes across distinct stages and proposed that the low microbial diversity in ephyra stage may be correlated with the high expression of the host-derived antimicrobial peptide aurelin. Furthermore, we recovered 43 high-quality metagenome-assembled genomes and determined the nutritional potential of the dominant Vibrio members. Interestingly, we observed increased abundances of genes related to the biosynthesis of amino acids, vitamins, and cofactors, as well as carbon fixation during the loss of host feeding ability, indicating the functional potential of Aurelia-associated microbiota to support the synthesis of essential nutrients. We also identified several potential mechanisms by which jellyfish-associated microbes establish stage-specific community structures and maintain stable colonization in dynamic host environments, including eukaryotic-like protein production, bacterial secretion systems, restriction-modification systems, and clustered regularly interspaced short palindromic repeats-Cas systems. Our study characterizes unique taxonomic and functional changes in jellyfish microbiomes during strobilation and provides foundations for uncovering the ancestral mechanism of host-microbe interactions during metamorphosis.

Characterizing the Impact of Cyanobacterial Blooms on the Photoreactivity of Surface Waters from New York Lakes: A Combined Statewide Survey and Laboratory Investigation.

Cyanobacterial blooms introduce autochthonous dissolved organic matter (DOM) into aquatic environments, but their impact on surface water photoreactivity has not been investigated through collaborative field sampling with comparative laboratory assessments. In this work, we quantified the apparent quantum yields (Φapp,RI) of reactive intermediates (RIs), including excited triplet states of dissolved organic matter (3DOM*), singlet oxygen (1O2), and hydroxyl radicals (•OH), for whole water samples collected by citizen volunteers from more than 100 New York lakes. Multiple comparisons tests and orthogonal partial least-squares analysis identified the level of cyanobacterial chlorophyll a as a key factor in explaining the enhanced photoreactivity of whole water samples sourced from bloom-impacted lakes. Laboratory recultivation of bloom samples in bloom-free lake water demonstrated that apparent increases in Φapp,RI during cyanobacterial growth were likely driven by the production of photoreactive moieties through the heterotrophic transformation of freshly produced labile bloom exudates. Cyanobacterial proliferation also altered the energy distribution of 3DOM* and contributed to the accelerated transformation of protriptyline, a model organic micropollutant susceptible to photosensitized reactions, under simulated sunlight conditions. Overall, our study provides insights into the relationship between the photoreactivity of surface waters and the limnological characteristics and trophic state of lakes and highlights the relevance of cyanobacterial abundance in predicting the photoreactivity of bloom-impacted surface waters.

Exposure to microplastics renders immunity of the thick-shell mussel more vulnerable to diarrhetic shellfish toxin-producing harmful algae.

Despite both microplastics (MPs) and harmful algae blooms (HABs) may pose a severe threat to the immunity of marine bivalves, the toxification mechanism underlying is far from being fully understood. In addition, owing to the prevalence and sudden occurrence characteristics of MPs and HABs, respectively, bivalves with MP-exposure experience may face acute challenge of harmful algae under realistic scenarios. However, little is known about the impacts and underlying mechanisms of MP-exposure experience on the susceptibility of immunity to HABs in bivalve mollusks. Taking polystyrene MPs and diarrhetic shellfish toxin-producing Prorocentrum lima as representatives, the impacts of MP-exposure on immunity vulnerability to HABs were investigated in the thick-shell mussel, Mytilus coruscus. Our results revealed evident immunotoxicity of MPs and P. lima to the mussel, as evidenced by significantly impaired total count, phagocytic activity, and cell viability of haemocytes, which may result from the induction of oxidative stress, aggravation of haemocyte apoptosis, and shortage in cellular energy supply. Moreover, marked disruptions of immunity, antioxidant system, apoptosis regulation, and metabolism upon MPs and P. lima exposure were illustrated by gene expression and comparative metabolomic analyses. Furthermore, the mussels that experienced MP-exposure were shown to be more vulnerable to P. lima, indicated by greater degree of deleterious effects on abovementioned parameters detected. In general, our findings emphasize the threat of MPs and HABs to bivalve species, which deserves close attention and more investigation.

Emerging Insights into Brevetoxicosis in Sea Turtles.

This review summarizes the current understanding of how brevetoxins, produced by Karenia brevis during harmful algal blooms, impact sea turtle health. Sea turtles may be exposed to brevetoxins through ingestion, inhalation, maternal transfer, and potentially absorption through the skin. Brevetoxins bind to voltage-gated sodium channels in the central nervous system, disrupting cellular function and inducing neurological symptoms in affected sea turtles. Moreover, the current evidence suggests a broader and longer-term impact on sea turtle health beyond what is seen during stranding events. Diagnosis relies on the detection of brevetoxins in tissues and plasma from stranded turtles. The current treatment of choice, intravenous lipid emulsion therapy, may rapidly reduce symptoms and brevetoxin concentrations, improving survival rates. Monitoring, prevention, and control strategies for harmful algal blooms are discussed. However, as the frequency and severity of blooms are expected to increase due to climate change and increased environmental pollution, continued research is needed to better understand the sublethal effects of brevetoxins on sea turtles and the impact on hatchlings, as well as the pharmacokinetic mechanisms underlying brevetoxicosis. Moreover, research into the optimization of treatments may help to protect endangered sea turtle populations in the face of this growing threat.

The secondary outbreak risk and mechanisms of Microcystis aeruginosa after H2O2 treatment.

The secondary outbreak of cyanobacteria after algicide treatment has been a serious problem to water ecosystems. Hydrogen peroxide (H2O2) is an algaecide widely used in practice, but similar re-bloom problems are inevitably encountered. Our work found that Microcystis aeruginosa (M. aeruginosa) temporarily hibernates after H2O2 treatment, but there is still a risk of secondary outbreaks. Interestingly, the dormant period was as long as 20 and 28 days in 5 mg L-1 and 20 mg L-1 H2O2 treatment groups, respectively, but the photosynthetic activity was both restored much earlier (within 14 days). Subsequently, a quantitative imaging flow cytometry-based method was constructed and confirmed that the re-bloom had undergone two stages including first recovery and then re-division. The expression of ftsZ and fabZ genes showed that M. aeruginosa had active transcription processes related to cell division protein and fatty acid synthesis during the dormancy stat. Furthermore, metabolomics suggested that the recovery of M. aeruginosa was mainly by activating folate and salicylic acid synthesis pathways, which promoted environmental stress resistance, DNA synthesis, and cell membrane repair. This study reported the comprehensive mechanisms of secondary outbreak of M. aeruginosa after H2O2 treatment. The findings suggest that optimizing the dosage and frequency of H2O2, as well as exploring the potential use of salicylic acid and folic acid inhibitors, could be promising directions for future algal control strategies.

Eco-friendly management of harmful cyanobacterial blooms in eutrophic lakes through vertical flow multi-soil-layering technology.

Eutrophication has led to the widespread occurrence of cyanobacterial blooms. Toxic cyanobacterial blooms with high concentrations of microcystins (MCs) have been identified in the Lalla Takerkoust reservoir in Morocco. The objective of this study was to evaluate the efficiency of the Multi-Soil-Layering (MSL) ecotechnology in removing natural cyanobacterial blooms from the lake. Two MSL pilots were used in rectangular glass tanks (60 × 10 × 70 cm). They consisted of permeable layers (PLs) made of pozzolan and a soil mixture layer (SML) containing local soil, ferrous metal, charcoal and sawdust. The main difference between the two systems was the type of local soil used: sandy soil for MSL1 and clayey soil for MSL2. Both MSL pilots effectively reduced cyanobacterial cell concentrations in the treated water to very low levels (0.09 and 0.001 cells/mL). MSL1 showed a gradual improvement in MC removal from 52 % to 99 %, while MSL2 started higher at 90 % but dropped to 54% before reaching 86%. Both MSL systems significantly reduced organic matter levels (97.2 % for MSL1 and 95.8 % for MSL2). Both MSLs were shown to be effective in removing cyanobacteria, MCs, and organic matter with comparable performance.

Photoprotection by photoinhibitory and PSII-reaction centre quenching controls growth of Ulva rigida (Chlorophyta) and is a pre-requisite for green tide formation.

MAIN CONCLUSION: The combined photoinhibitory and PSII-reaction centre quenching against light stress is an important mechanism that allows the green macroalga Ulva rigida to proliferate and form green tides in coastal ecosystems. Eutrophication of coastal ecosystems often stimulates massive and uncontrolled growth of green macroalgae, causing serious ecological problems. These green tides are frequently exposed to light intensities that can reduce their growth via the production of reactive oxygen species (ROS). To understand the physiological and biochemical mechanisms leading to the formation and maintenance of green tides, the interaction between inorganic nitrogen (Ni) and light was studied. In a bi-factorial physiological experiment simulating eutrophication under different light levels, the bloom-forming green macroalga Ulva rigida was exposed to a combination of ecologically relevant nitrate concentrations (3.8-44.7 µM) and light intensities (50-1100 µmol photons m-2 s-1) over three days. Although artificial eutrophication (≥ 21.7 µM) stimulated nitrate reductase activity, which regulated both nitrate uptake and vacuolar storage by a feedback mechanism, nitrogen assimilation remained constant. Growth was solely controlled by the light intensity because U. rigida was Ni-replete under oligotrophic conditions (3.8 µM), which requires an effective photoprotective mechanism. Fast declining Fv/Fm and non-photochemical quenching (NPQ) under excess light indicate that the combined photoinhibitory and PSII-reaction centre quenching avoided ROS production effectively. Thus, these mechanisms seem to be key to maintaining high photosynthetic activities and growth rates without producing ROS. Nevertheless, these photoprotective mechanisms allowed U. rigida to thrive under the contrasting experimental conditions with high daily growth rates (12-20%). This study helps understand the physiological mechanisms facilitating the formation and persistence of ecologically problematic green tides in coastal areas.

Can exposure to Gymnodinium catenatum toxic blooms influence the impacts induced by Neodymium in Mytilus galloprovincialis mussels? What doesn't kill can make them stronger?

The presence in marine shellfish of toxins and pollutants like rare earth elements (REEs) poses a major threat to human well-being, coastal ecosystems, and marine life. Among the REEs, neodymium (Nd) stands out as a widely utilized element and is projected to be among the top five critical elements by 2025. Gymnodinum catenatum is a phytoplankton species commonly associated with the contamination of bivalves with paralytic shellfish toxins. This study evaluated the biological effects of Nd on the mussel species Mytilus galloprovincialis when exposed to G. catenatum cells for fourteen days, followed by a recovery period in uncontaminated seawater for another fourteen days. After co-exposure, mussels showed similar toxin accumulation in the Nd and G. catenatum treatment in comparison with the G. catenatum treatment alone. Increased metabolism and enzymatic defenses were observed in organisms exposed to G. catenatum cells, while Nd inhibited enzyme activity and caused cellular damage. Overall, this study revealed that the combined presence of G. catenatum cells and Nd, produced positive synergistic effects on M. galloprovincialis biochemical responses compared to G. catenatum alone, indicating that organisms' performance may be significantly modulated by the presence of multiple co-occurring stressors, such those related to chemical pollution and harmful algal blooms. ENVIRONMENTAL IMPLICATIONS: Neodymium (Nd) is widely used in green technologies like wind turbines, and this element's potential threats to aquatic environments are almost unknown, especially when co-occurring with other environmental factors such as blooms of toxic algae. This study revealed the cellular impacts induced by Nd in the bioindicator species Mytilus galloprovincialis but further demonstrated that the combination of both stressors can generate a positive defense response in mussels. The present findings also demonstrated that the impacts caused by Nd lasted even after a recovery period while a previous exposure to the toxins generated a faster biochemical improvement by the mussels.

Establishment of a graphene oxide-assisted nucleic acid chromatography strip detection technology for Prorocentrum minimum.

In recent decades, the harmful algal blooms (HABs) caused by Prorocentrum minimum have caused serious environmental damage and economic losses. The detection of P. minimum plays an important role in warning the outbreak of P. minimum-forming HABs. By utilizing the powerful absorption of graphene oxide (GO) on short-stranded DNA, a GO-assisted nucleic acid chromatography strip (GO-NACS) was proposed here to achieve a highly sensitive, specific, intuitive, and convenient detection of P. minimum. In particular, this study used our previously reported conventional-NACS (C-NACS) as a control to evaluate the improvement of detection performance with the use of GO. The performance of GO-NACS was evaluated from the perspectives of specificity, sensitivity, stability, and practicality. The specificity test demonstrated that it had a high degree of specificity and did not display cross-reacting with non-target algal species. The sensitivity test with the genomic DNA indicated that it had a detection limit of 1.30 × 10-3 ng µL-1, representing a 10-fold higher sensitivity than C-NACS and a 100-fold higher sensitivity than agarose gel electrophoresis (AGE). The interference test with non-target algal species demonstrated that it had a good detection stability, and the interfering algal species had no obvious effect on the detection of P. minimum. The practicality test with simulated natural water samples showed that the cellular detection limit of GO-NACS was 6.8 cells mL-1, which was 10-fold and 100-fold lower than that of C-NACS and AGE, respectively. In conclusion, the established GO-NACS may offer a novel alternative technique for the detection of P. minimum while guaranteeing specificity and enhancing sensitivity without requiring extensive apparatus.

Weakened hydrological oscillation period increased the frequency of river algal blooms.

The evolution of riverine aquatic ecosystems typically exhibits notable characteristic with cumulative, enduring, and hysteresis. Exploring the non-linear response of riverine ecology to long-term hydrological fluctuations become a major challenge in contemporary interdisciplinary research. In response to the critical issue of frequent river algal blooms in the lower Han River, which is impacted by Asian largest inter-basin water diversion project. We identified the non-linear response of eco-hydrology across various time scales through the integration of Continuous Wavelet Transform (CWT) and Inverse Wavelet Transform (IWT). Our study revealed that: 1) Over the past half century, the hydrological regime in the lower Han river showed a significant downward trend, and existed three significant hydrological oscillation periods (HOPs), including the short-scale Intra-AC (180 days), the medium-scale AC (365 days, the first major period), and the long-scale Inter-AC (2500 days), the variation of Inter-AC changed most dramatically. 2) We further found that the Inter-AC variation of hydrology is more closely related to the formation of river algal blooms in the Han River, and when the hydrological Inter-AC shows steady state or downward trend, the frequency of algal blooms in the lower Han River increases significantly. 3) The river algal blooms in the lower Han River is a cumulative consequence to the long-term hydrological influences. Weakened hydrological Inter-AC is more likely to increase the frequency of river algal blooms, and 10-years Inter-AC cumulation increased the frequency by 60%. Therefore, the weaken of long-scale HOP will significantly increase the frequency of river algal blooms in the future. This study received a critical scientific insight and aimed at provide guidance for the optimization of ecological management within the framework of national large-scale water conservation.

Understanding the risks of co-exposures in a changing world: a case study of dual monitoring of the biotoxin domoic acid and Vibrio spp. in Pacific oyster.

Assessing the co-occurrence of multiple health risk factors in coastal ecosystems is challenging due to the complexity of multi-factor interactions and limited availability of simultaneously collected data. Understanding co-occurrence is particularly important for risk factors that may be associated with, or occur in similar environmental conditions. In marine ecosystems, the co-occurrence of harmful algal bloom toxins and bacterial pathogens within the genus Vibrio may impact both ecosystem and human health. This study examined the co-occurrence of Vibrio spp. and domoic acid (DA) produced by the harmful algae Pseudo-nitzschia by (1) analyzing existing California Department of Public Health monitoring data for V. parahaemolyticus and DA in oysters; and (2) conducting a 1-year seasonal monitoring of these risk factors across two Southern California embayments. Existing public health monitoring efforts in the state were robust for individual risk factors; however, it was difficult to evaluate the co-occurrence of these risk factors in oysters due to low number of co-monitoring instances between 2015 and 2020. Seasonal co-monitoring of DA and Vibrio spp. (V. vulnificus or V. parahaemolyticus) at two embayments revealed the co-occurrence of these health risk factors in 35% of sampled oysters in most seasons. Interestingly, both the overall detection frequency and co-occurrence of these risk factors were considerably less frequent in water samples. These findings may in part suggest the slow depuration of Vibrio spp. and DA in oysters as residual levels may be retained. This study expanded our understanding of the simultaneous presence of DA and Vibrio spp. in bivalves and demonstrates the feasibility of co-monitoring different risk factors from the same sample. Individual programs monitoring for different risk factors from the same sample matrix may consider combining efforts to reduce cost, streamline the process, and better understand the prevalence of co-occurring health risk factors.

[Analysis of the Spatiotemporal Distribution of Algal Blooms and Its Driving Factors in Chaohu Lake Based on Multi-source Datasets].

Eutrophication and harmful algae blooms are one of the common ecological and environmental problems faced by freshwater lakes all over the world. As a typical inland freshwater lake, Chaohu Lake exhibits a high level of eutrophication and algae blooms year-round and shows a spatiotemporal difference in different regions of the lake. In order to understand the basic regularity of the development and outbreak of algal blooms in Chaohu Lake, the data from the comprehensive water observation platform and remote sensing were integrated to obtain the spatiotemporal distribution of algal blooms from 2015 to 2020. Then, an evaluation model based on Boosted Regression Trees (BRT) was constructed to quantitatively assess the importance and interactions of various environmental factors on algal blooms at different stages. The results indicated that:① The occurrence of algal blooms in Chaohu Lake exhibited significant seasonal variations, with the cyanobacteria beginning to recover in spring and bring about a light degree of algal blooms in the western and coastal areas of Chaohu Lake. The density of cyanobacteria reached its maximum in summer and autumn, accompanied by moderate and severe degrees of algal bloom outbreaks. ② During the non-outbreak period, the variation in the cyanobacteria density was greatly affected by physical and chemical factors, which explained 80.3% of the variance in the change in cyanobacteria density. The high concentrations of dissolved oxygen content in the water column and the weak alkalinity (7.2-7.6) and appropriate water temperature (about 3℃) provided a favorable environmental condition for the breeding and growth of cyanobacteria. In addition, the onset of algal blooms was closely related to the air temperature steadily passing through the threshold. According to the statistics, the date of first outbreak of algal blooms in Chaohu Lake was 11 days or so after the air temperature steadily remained above 7℃. ③ During the outbreak period, the occurrence of algal blooms was influenced by the combination of cyanobacterial biomass and meteorological conditions such as temperature, wind speed, and sunshine duration. The cumulative contribution ratio of the four factors was as high as 95%, and each factor had an optimal interval conductive to the outbreak of algal blooms. Furthermore, the results of multi-factor interaction analysis indicated a larger probability of the outbreak of algal blooms in Chaohu Lake under the combined effect of high cyanobacteria density, suitable temperature, and the breeze. This study analyzed and revealed the spatiotemporal characteristics and the dominant influencing factors of algal blooms in Chaohu Lake at different stages, which could provide the scientific basis for the prediction, early warning, and disposal of algal blooms under the context of climate change.

Phenotypic and Genotypic Methods for the Identification and Quantification of Cyanobacteria in Lake Water.

Early monitoring of Microcystis, a cyanobacterium that produces microcystin, is paramount in order to confirm the presence of Microcystis spp. Both phenotypic and genotypic methods have been used. The phenotypic methods provide the presence of the microcystis but do not confirm its species type and toxin produced. Additionally, phenotypic methods cannot differentiate toxigenic from non-toxigenic Microcystis. Therefore, the current protocol also describes genetic methods based on PCR to detect toxigenic Microcystis spp. based on microcystin synthetase E (mcy E) gene and 16-23S RNA genes for species-specific identification, which can effectively comprehend distinct lineages and discrimination of potential complexity of microcystin populations. The presence of these microcystin toxins in blood, in most cases, indicates contamination of drinking water by cyanobacteria. The methods presented herein are used to identify microcystin toxins in drinking water and blood.

An On-Farm Workflow for Predictive Management of Paralytic Shellfish Toxin-Producing Harmful Algal Blooms for the Aquaculture Industry.

Paralytic shellfish toxins (PSTs) produced by marine dinoflagellates significantly impact shellfish industries worldwide. Early detection on-farm and with minimal training would allow additional time for management decisions to minimize economic losses. Here, we describe and test a standardized workflow based on the detection of sxtA4, an initial gene in the biosynthesis of PSTs. The workflow is simple and inexpensive and does not require a specialized laboratory. It consists of (1) water collection and filtration using a custom gravity sampler, (2) buffer selection for sample preservation and cell lysis for DNA, and (3) an assay based on a region of sxtA, DinoDtec lyophilized quantitative polymerase chain reaction (qPCR) assay. Water samples spiked with Alexandrium catenella showed a cell recovery of >90% when compared to light microscopy counts. The performance of the lysis method (90.3% efficient), Longmire's buffer, and the DinoDtec qPCR assay (tested across a range of Alexandrium species (90.7-106.9% efficiency; r2 > 0.99)) was found to be specific, sensitive, and efficient. We tested the application of this workflow weekly from May 2016 to 30th October 2017 to compare the relationship between sxtA4 copies L-1 in seawater and PSTs in mussel tissue (Mytilus galloprovincialis) on-farm and spatially (across multiple sites), effectively demonstrating an ∼2 week early warning of two A. catenella HABs (r = 0.95). Our tool provides an early, accurate, and efficient method for the identification of PST risk in shellfish aquaculture.

Enhancing water quality prediction for fluctuating missing data scenarios: A dynamic Bayesian network-based processing system to monitor cyanobacteria proliferation.

Tackling the impact of missing data in water management is crucial to ensure the reliability of scientific research that informs decision-making processes in public health. The goal of this study is to ascertain the root causes associated with cyanobacteria proliferation under major missing data scenarios. For this purpose, a dynamic missing data management methodology is proposed using Bayesian Machine Learning for accurate surface water quality prediction of a river from Limia basin (Spain). The methodology used entails a sequence of analytical steps, starting with data pre-processing, followed by the selection of a reliable dynamic Bayesian missing value prediction system, leading finally to a supervised analysis of the behavioral patterns exhibited by cyanobacteria. For that, a total of 2,118,844 data points were used, with 205,316 (9.69 %) missing values identified. The machine learning testing showed the iterative structural expectation maximization (SEM) as the best performing algorithm, above the dynamic imputation (DI) and entropy-based dynamic imputation methods (EBDI), enhancing in some cases the accuracy of imputations by approximately 50 % in R2, RMSE, NRMSE, and logarithmic loss values. These findings can impact how data on water quality is being processed and studied, thus, opening the door for more reliable water management strategies that better inform public health decisions.

Long-term studies on West Antarctic Peninsula phytoplankton blooms suggest range shifts between temperate and polar species.

The Western Antarctic Peninsula (WAP) experiences one of the highest rates of sea surface warming globally, leading to potential changes in biological communities. Long-term phytoplankton monitoring in Potter Cove (PC, King George Island, South Shetlands) from the 1990s to 2009 revealed consistently low biomass values, and sporadic blooms dominated by cold-water microplankton diatoms. However, a significant change occurred between 2010 and 2020, marked by a notable increase in intense phytoplankton blooms in the region. During this period, the presence of a nanoplankton diatom, Shionodiscus gaarderae, was documented for the first time. In some instances, this species even dominated the blooms. S. gaarderae is recognized for producing blooms in temperate waters in both hemispheres. However, its blooming in the northern Southern Ocean may suggest either a recent introduction or a range shift associated with rising temperatures in the WAP, a phenomenon previously observed in experimental studies. The presence of S. gaarderae could be viewed as a warning sign of significant changes already underway in the northern WAP plankton communities. This includes the potential replacement of microplankton diatoms by smaller nanoplankton species. This study, based on observations along the past decade, and compared to the previous 20 years, could have far-reaching implications for the structure of the Antarctic food web.

Dynamics of Microcystis surface scum formation under different wind conditions: the role of hydrodynamic processes at the air-water interface.

Due to climate change, Microcystis blooms occur at increasing frequencies in aquatic ecosystems worldwide. Wind-generated turbulence is a crucial environmental stressor that can vertically disperse the Microcystis surface scum, reducing its light availability. Yet, the interactions of Microcystis scum with the wind-generated hydrodynamic processes, particularly those at the air-water interface, remain poorly understood. Here, we explore the response of Microcystis (including colony size and migration dynamics) to varying magnitudes and durations of intermittent wind disturbances in a mesocosm system. The flow velocities, size of Microcystis colonies, and the areal coverage of the water surface by scum were measured through video observations. Our results demonstrate that low wind speeds increase colony size by providing a stable condition where Microcystis forms a scum layer and aggregates into large colonies at the air-water interface. In contrast, wind disturbances disperse scum and generate turbulence, resulting in smaller colonies with higher magnitudes of wind disturbance. We observed that surface scum can form rapidly following a long period (6 h) of high-magnitude (4.5 m s-1) wind disturbance. Furthermore, our results indicate reduced water surface tension caused by the presence of Microcystis, which can decrease surface flow velocity and counteract wind-driven mixing. The reduced surface tension may also drive lateral convection at the water surface. These findings suggest that Microcystis reduces surface tension, likely by releasing surface-active materials, as an adaptive response to various wind conditions. This could result in an increased rate of surface scum re-formation under wind conditions and potentially facilitate the lateral expansion of scum patches during weak wind periods. This study reveals new insights into how Microcystis copes with different wind conditions and highlights the importance of the air-water interface for Microcystis scum dynamics.

Detection of Anatoxins in Human Urine by Liquid Chromatography Triple Quadrupole Mass Spectrometry and ELISA.

Harmful cyanobacterial blooms are becoming more common and persistent around the world. When in bloom, various cyanobacterial strains can produce anatoxins in high concentrations, which, unlike other cyanobacterial toxins, may be present in clear water. Potential human and animal exposures to anatoxins occur mainly through unintentional ingestion of contaminated algal mats and water. To address this public health threat, we developed and validated an LC-MS/MS method to detect anatoxins in human urine to confirm exposures. Pooled urine was fortified with anatoxin-a and dihydroanatoxin at concentrations from 10.0 to 500 ng/mL to create calibrators and quality control samples. Samples were diluted with isotopically labeled anatoxin and solvent prior to LC-MS/MS analysis. This method can accurately quantitate anatoxin-a with inter- and intraday accuracies ranging from 98.5 to 103% and relative standard deviations < 15%, which is within analytical guidelines for mass spectrometry methods. Additionally, this method qualitatively detects a common degradation product of anatoxin, dihydroanatoxin, above 10 ng/mL. We also evaluated a commercial anatoxin-a ELISA kit for potential diagnostic use; however, numerous false positives were detected from unexposed individual human urine samples. In conclusion, we have developed a method to detect anatoxins precisely and accurately in urine samples, addressing a public health area of concern, which can be applied to future exposure events.

Experimental warming promotes phytoplankton species sorting towards cyanobacterial blooms and leads to potential changes in ecosystem functioning.

A positive feedback loop where climate warming enhances eutrophication and its manifestations (e.g., cyanobacterial blooms) has been recently highlighted, but its consequences for biodiversity and ecosystem functioning are not fully understood. We conducted a highly replicated indoor experiment with a species-rich subtropical freshwater phytoplankton community. The experiment tested the effects of three constant temperature scenarios (17, 20, and 23 °C) under high-nutrient supply conditions on community composition and proxies of ecosystem functioning, namely resource use efficiency (RUE) and CO2 fluxes. After 32 days, warming reduced species richness and promoted different community trajectories leading to a dominance by green algae in the intermediate temperature and by cyanobacteria in the highest temperature treatments. Warming promoted primary production, with a 10-fold increase in the mean biomass of green algae and cyanobacteria. The maximum RUE occurred under the warmest treatment. All treatments showed net CO2 influx, but the magnitude of influx decreased with warming. We experimentally demonstrated direct effects of warming on phytoplankton species sorting, with negative effects on diversity and direct positive effects on cyanobacteria, which could lead to potential changes in ecosystem functioning. Our results suggest potential positive feedback between the phytoplankton blooms and warming, via lower net CO2 sequestration in cyanobacteria-dominated, warmer systems, and add empirical evidence to the need for decreasing the likelihood of cyanobacterial dominance.

Unveiling the trifecta of cyanobacterial quorum sensing: LuxI, LuxR and LuxS as the intricate machinery for harmful algal bloom formation in freshwater ecosystems.

Harmful algal blooms (HABs) are causing significant disruptions in freshwater ecosystems, primarily due to the proliferation of cyanobacteria. These blooms have a widespread impact on various lakes globally, leading to profound environmental and health consequences. Cyanobacteria, with their ability to produce diverse toxins, pose a particular concern as they negatively affect the well-being of humans and animals, exacerbating the situation. Notably, cyanobacteria utilize quorum sensing (QS) as a complex communication mechanism that facilitates coordinated growth and toxin production. QS plays a critical role in regulating the dynamics of HABs. However, recent advances in control and mitigation strategies have shown promising results in effectively managing and reducing the occurrence of HABs. This comprehensive review explores the intricate aspects of cyanobacteria development in freshwater ecosystems, explicitly focusing on deciphering the signaling molecules associated with QS and their corresponding genes. Furthermore, a concise overview of diverse measures implemented to efficiently control and mitigate the spread of these bacteria will be provided, shedding light on the ongoing global efforts to address this urgent environmental issue. By deepening our understanding of the mechanisms driving cyanobacteria growth and developing targeted control strategies, we hope to safeguard freshwater ecosystems and protect the health of humans and animals from the detrimental impacts of HABs.