Cyanobacterial blooms

Comprehensive Raman spectroscopy analysis for differentiating toxic cyanobacteria through multichannel 1D-CNNs and SHAP-based explainability

Cyanobacterial blooms pose significant environmental and public health risks due to the production of toxins that contaminate water sources and disrupt aquatic ecosystems. Rapid and accurate identification of cyanobacterial species is crucial for effective monitoring and management strategies. In this study, we combined Raman spectroscopy with deep learning techniques to classify four toxic cyanobacterial species: Dolichospermum crassum, Aphanizomenon sp., Planktothrix agardhii and Microcystis aeruginosa. Spectral data were acquired using a confocal Raman microscope with a 532 nm excitation wavelength and subjected to preprocessing and filtering to enhance signal quality. We evaluated a multichannel one-dimensional convolutional neural network (1D-CNN) approach that incorporates raw spectra, baseline estimations, and preprocessed spectra. This multichannel approach improved overall classification accuracy, achieving 86% compared to 74% with a traditional single-channel 1D-CNN using only preprocessed spectra while maintaining low overfitting. Shapley Additive exPlanations (SHAP) were applied to identify critical spectral regions for classification to enhance interpretability. These findings highlight the potential of combining Raman spectroscopy with explainable deep learning methods as a powerful tool for water quality monitoring and the early detection of Harmful Algal Blooms (HABs).

Vigilance against climate change-induced regime shifts for phosphorus restoration in shallow lake ecosystems

The dual pressure of anthropogenic activities and frequent extreme weather events has triggered a transition from macrophyte to algal dominance in shallow lakes. Phosphorus (P) is the key driver of regime shifts that can lead to a decline in the stability and resilience of lake ecosystems. However, the mechanisms underlying such regime shifts, and the effects of state transitions on internal P loading during macrophyte restoration in large shallow eutrophic lakes, remain to be fully elucidated. This study utilised long-term in situ monitoring data, across three distinct lake states (bare ground, macrophyte-dominated stage, and algae-dominated stage) to elucidate the accumulation and release mechanisms of sedimentary P during regime shifts. The findings demonstrated that the rehabilitation of submerged plants efficiently reduced internal P loading (water column P, sediment P fractions, and P flux), while the persistence of algal blooms was driven by the reductive release of Fe-P from sediments and the dissolution of Al-P from suspended particulate matter. High temperature, low dissolved oxygen, and high pH largely modulate the pathways and mechanisms of P supply during regime shifts. The combined pressures of extreme weather (heavy rainfall, strong winds, and extreme heat) and trophic cascades from fish stocking can trigger a shift from macrophytes to algae in shallow lakes. Appropriate management of the structure and biomass of aquatic animal communities (e.g., small-bodied or omnibenthivorous fish) and optimization of the food web structure can effectively improve water quality and maintain ecosystem stability. These findings enrich the theoretical understanding of regime-shift mechanisms from an ecosystem perspective and offer novel insights into P remediation in large shallow eutrophic lakes.

Effects of extracellular organic matter from bacteria on the growth, physiology, photosynthesis, and transcriptome of the bloom-forming algal species

Cyanobacterial blooms pose one of the most severe ecological challenges in aquatic systems. However, the mechanism through which bacterial dissolved organic matter influences the formation of algal blooms remains unclear. In this study, extracellular organic matter (EOM) was extracted from Flavobacterium sp., a common bacterial group in bloom, and the impacts of this EOM on the growth, physiology, photosynthesis, and transcriptome of Anabaena sp. were investigated. The results indicated that flavobacterium-derived EOM (F-EOM) inhibited Anabaena sp. growth, physiological activity, and photosynthesis, with greater inhibition at higher concentrations. Meanwhile, transcriptome analysis showed that 803 genes in Anabaena sp. were differentially expressed after being exposed to 10 mg/L F-EOM, with simultaneously the majority being down-regulated. The down-regulation of genes in photochemical reactions, the synthesis of photosynthetic pigment, and light-trapping antenna protein inhibited photosynthesis. While ATP synthesis was reduced due to the genes related to oxidative phosphorylation and the tricarboxylic acid cycle was downregulated. Moreover, the down-regulated genes in amino acid synthesis affected the synthesis of proteins and metabolic regulatory factors. This may be the main reason why F-EOM could hinder the growth and metabolism of Anabaena sp. These results provide scientific insights into the formation and control of cyanobacteria blooms.

Climate change promotes harmful algal blooms in China's lakes and reservoirs despite significant nutrient control efforts

The increasing frequency and magnitude of harmful algal blooms (HABs) threatens the integrity of aquatic ecosystem functioning and human health worldwide. Nutrient reduction strategies have been widely used to mitigate HABs, but their efficiency in light of on-going changes in climate remains unclear. Here, we assembled an 18-year (2005-2022) national water quality dataset for 97 lakes across China. We examined the dynamics of HABs and their response to nutrient reduction under historical climate change trends using a combination of statistical and process-based modeling. The results revealed an increase in HABs despite a widespread decline in ambient nutrient levels, with 80.5 % of lakes experiencing a decline in phosphorus but 61.8 % displaying an increase in Chlorophyll a concentrations. We attributed this counterintuitive trend to climatic warming, which can hinder the mitigation of HABs until the ambient nutrients reach sufficiently low levels. The extent of HAB promotion by warming varied spatially, with a distinctly greater proliferation in China's lower-latitude lakes (<35°N), primarily due to the prevailing warmer temperatures. Notwithstanding the persistence of HABs in China's lakes, national-scale modeling suggests that nutrient loading control remains valuable in protecting our water resources, as the HAB risk would have been 32.6 % higher due to climate change. The anticipated future nutrient reduction efforts in China are expected to alleviate higher latitude lakes from frequent HAB occurrences, but lower latitude lakes will still face considerable HAB risks. Our national-scale assessment demonstrates a variant efficiency of nutrient reduction in offsetting HAB risks amid rapid climate change, and highlights the need of adaptively enhancing our mitigation strategies in response to the ever-changing ecological conditions.

Human-induced N-P imbalances will aggravate GHG emissions from lakes and reservoirs under persisting eutrophication

Lakes and reservoirs are hotspots for emissions of atmospheric greenhouse gas (GHG) such as CO2, CH4, and N2O, and their nutrient levels and stoichiometric status are significant drivers of GHG emissions. In recent decades, human-induced unbalanced inputs of nitrogen (N) and phosphorus (P) have enhanced the P-limiting state of inland lake and reservoir systems. However, it remains unclear whether this state transition involves global changes in nutrient-limiting systems and GHG emissions from lakes and reservoirs. In this study, a comprehensive model was developed to examine the relationship between GHG fluxes and total N (TN) and total P (TP) to predict future human-induced N over-enrichment and its impact on global GHG emissions. Our results show that excess N inputs amplified GHG emissions, with future water eutrophication (1.2×) projected to increase CO2 emissions (384.66 Tg·y-1), CH4 (7.38 Tg·y-1), and N2O (0.23 Tg·y-1) from lakes and reservoirs by 49 %, 12 %, and 25 %, respectively, amounting to approximately US$0.13 trillion ($0.08-6.91 trillion, 2015$) in social costs. A future 50 % increase in N: P will increase the relative social cost of carbon by 15 % compared to future 1.2× eutrophication levels. Given the social costs and benefits of reducing N and P pollutants in water individually and in synchronization, future long-term strategies for managing eutrophication in lakes and reservoirs need to emphasize balanced control of N and P.

Management of cyanobacteria and cyanotoxins in drinking water: A comprehensive review on occurrence, toxicity, challenges and treatment approaches

The synergistic effects of increased anthropogenic activities and climate change have intensified the frequency of cyanobacterial blooms in surface water bodies. These blooms pose significant health risks to humans and animals due to the release of cyanotoxins into the water. Conventional drinking water treatment plants (DWTPs) are often ineffective in removing cyanobacterial cells due to challenges such as electrostatic repulsion, hydrophilicity, and buoyancy. While excessive pre-oxidation can remove cyanobacteria, it may cause cell lysis, increase cyanotoxin concentration, and surpass various regulatory guidelines, posing additional risks of forming disinfection by-products (DBPs). Moderate pre-oxidation presents a viable alternative by effectively removing intact cyanobacterial cells. This review comprehensively analyses the occurrence, toxicity, associated challenges faced by DWTPs, and treatment approaches for cyanobacteria. Various moderate pre-oxidation processes for enhancing coagulation efficiency while preserving cell integrity are systematically summarized and critically discussed. The review also highlights the importance of holistic multi-barrier approaches, including prevention, corrections measures and water intake management for managing cyanobacterial contamination in drinking water treatment. It underscores the need for intensive research to develop affordable and effective solutions to ensure sustainable and safe drinking water provision.

Monitoring phycocyanin in global inland waters by remote sensing: Progress and future developments

Cyanobacterial blooms are increasingly becoming major threats to global inland aquatic ecosystems. Phycocyanin (PC), a pigment unique to cyanobacteria, can provide important reference for the study of cyanobacterial blooms warning. New satellite technology and cloud computing platforms have greatly improved research on PC, with the average number of studies examining it having increased from 5 per year before 2018 to 17 per year thereafter. Many empirical, semi-empirical, semi-analytical, quasi-analytical algorithm (QAA) and machine learning (ML) algorithms have been developed based on unique absorption characteristics of PC at approximately 620 nm. However, most models have been developed for individual lakes or clusters of them in specific regions, and their applicability at greater spatial scales requires evaluation. A review of optical mechanisms, principles and advantages and disadvantages of different model types, performance advantages and disadvantages of mainstream sensors in PC remote sensing inversion, and an evaluation of global lacustrine PC datasets is needed. We examine 230 articles from the Web of Science citation database between 1900 and 2024, summarize 57 of them that deal with construction of PC inversion models, and compile a list of 6526 PC sampling sites worldwide. This review proposed the key to achieving global lacustrine PC remote sensing inversion and spatiotemporal evolution analysis is to fully use existing multi-source remote sensing big data platforms, and a deep combination of ML and optical mechanisms, to classify the object lakes in advance based on lake optical characteristics, eutrophication level, water depth, climate type, altitude, population density within the watershed. Additionally, integrating data from multi-source satellite sensors, ground-based observations, and unmanned aerial vehicles, will enable future development of global lacustrine PC remote estimation, and contribute to achieving United Nations Sustainable Development Goals inland water goals.

Primary producers in freshwater ecosystem respond differently to multiple environmental stressors: A mesocosm study

Primary producers play key roles in maintaining a clear-water phase and promoting biodiversity in shallow aquatic ecosystems. Environmental stressors from anthropogenic activities, such as eutrophication and pesticide pollution, individually and in combination, can drive these ecosystems into a turbid state, potentially leading to a regime shift. In this 111-day study, we used 40 mesocosms (200 L) to simulate shallow lakes dominated by two typical macrophytes: the bottom-dwelling densely Vallisneria denseserrulata and the floating Spirodela polyrrhiza, along with associated food web components. We tested the interactive effects of nutrient loading, glyphosate-based herbicides, and imidacloprid insecticides on the growth of aquatic plants, phytoplankton, and periphyton. Our results indicate that meso-eutrophication, glyphosate and imidacloprid directly or indirectly affected aquatic primary producers, with the type of interaction (synergistic, antagonistic and additive) related to the form of the primary producer. Meso-eutrophication alone increased the biomass of all organisms except submerged plants, glyphosate alone decreased the biomass of all organisms except phytoplankton, with particularly strong effects on aquatic plants, and imidacloprid alone affected only aquatic animals. While combinations of multiple stressors generally increased algal biomass and decreased macrophyte biomass, submerged macrophytes consistently helped control algal blooms. These results demonstrate the risk of algal blooms in shallow lakes within agricultural landscapes and emphasize the crucial role of macrophytes in preventing algal blooms and maintaining healthy lake ecosystems.

Modelling harmful algal blooms in a mono- and a polydominant eutrophic lake under temperature and nutrient changes

Cyanobacterial blooms, driven by nutrient loading and temperature, pose significant ecological and economic challenges. This study employs a combined data-driven and trait-based modelling approach to predict changes in cyanobacterial communities in a mono- and a polydominant shallow temperate lakes under varying temperature and nutrient scenarios. Results of the AQUATOX simulation model for two aquatic systems suggest that a 2 °C temperature increase, consistent with Intergovernmental Panel on Climate Change's predictions, may influence cyanobacteria species composition and dominance, with trends indicating a possible shift favouring Nostocales over Oscillatoriales and Chroococcales. Temperature increases by 4 °C clearly promoted the dominance of Nostocales. Nutrient dynamics appear to influence community structure. In a nutrient-rich monodominant lake, temperature was the primary driver, while in a nutrient-limited polydominant lake, phosphorus availability influenced cyanobacteria species dominance. Combined warming and phosphorus alterations significantly affected cyanobacteria bloom intensity and duration, particularly enhancing Nostocales growth. The study highlights the complexity of cyanobacterial responses to climate change, emphasizing the need for more analysis and comprehensive models to predict harmful algal blooms (HABs) in freshwater ecosystems. While the findings suggest that temperature and nutrient availability may be critical drivers of cyanobacterial dominance, additional research across a broader range of systems is necessary.

Occurrence and risk assessment of different cyanotoxins and their relationship with environmental factors in six typical eutrophic lakes of China

Cyanobacterial blooms can generate various toxic metabolites in freshwater, and pose serious threats to drinking water safety and human health. Although microcystins (MCs) have been detected in many freshwater ecosystems in China, little is known about the other cyanotoxins. An investigation of six eutrophic lakes (i.e. Hulun Lake, Wuliangsuhai Lake, Chaohu Lake, Taihu Lake, Xingyun Lake, and Dianchi Lake) in different geographical locations of China was performed during the summer of 2022 to determine the occurrence of various cyanotoxins (i.e. anatoxin-a (ATX), cylindrospermopsin (CYN), and MCs) in water column and their possible risks, and to evaluate the related environmental factors. MCs levels in sediment of these lakes were also investigated. MCs were the primary cyanotoxins in the water column of investigated lakes. The mean MCs contents in water column of Hulun Lake, Wuliangsuhai Lake, Chaohu Lake, Taihu Lake, Xingyun Lake, and Dianchi Lake were 3.61, 0.13, 3.60, 2.18, 0.57, and 2.56 μg/L, respectively. The total MCs levels in water column exceeded 1 μg/L in some areas of these lakes except Wuliangsuhai Lake. Replete nitrogen and/or phosphorus levels seemed to be related to MCs production. ATX can be detected in these lakes except Xingyun Lake at ng/L levels. CYN can be detected in all lakes at ng/L levels. However, the levels of ATX and CYN appear to be not significantly associated with environmental factors. MCs and CYN can pose a high or moderate risk for humans and aquatic organisms in some areas of these lakes, while ATX can pose a low or no risk for humans and aquatic organisms in most areas of these lakes. MCs can also be detected in sediment of all lakes at ng/g levels. This research emphasizes the necessity for long-term monitoring of different cyanotoxins in eutrophic lakes, and the implementation of nutrient control and management strategies.

Extreme marine heatwave linked to mass fish kill in the Red Sea

Anthropogenic climate change has precipitated an increase in marine heatwaves (MHWs) that have significant and multifaceted impacts on marine ecosystems. In late August 2023, an intense heatwave coincided with a mass fish kill event on the Saudi Arabian coast of the central Red Sea. Here, we compile MHW metrics from satellite data to illustrate the mortality event was linked with the most intense period of rapid heating in the central Red Sea in recent history. Using field surveys, we quantified the impact of the event on the fish community and found that nearly 1000 fish washed ashore along a 60 km stretch of coastline. Representatives of 54 species were detected, which illustrates the impact of the MHW event on a broad range of fishes. The exact cause of mortality during the event is unknown, but likely related to temperature-induced physiological stress and associated factors. Sparse coastal monitoring limited our ability to rapidly respond to the event and document the proximate cause of mortality. This study not only sheds light on the immediate impacts of a MHW on components of a coral reef ecosystem, but also emphasizes the broader ecological consequences. Mass fish kills may have cascading impacts on ecosystem functioning by causing shifts in community structure and a decrease in biodiversity, which can undermine both the ecological functioning and economic stability of marine-dependent regions. This may be especially true for reefs already occupying a thermal niche that approaches the upper limits of many species, such as those in the Red Sea. Our study highlights the critical need for enhanced reporting mechanisms and forecasting tools to effectively document and help mitigate further impacts linked to MHW-induced mass marine die-offs.

Weak salinization alleviates the harmful impact of cyanobacteria on water fleas

Climate change and anthropogenic activities are driving dramatic changes in aquatic ecosystems. In this context, cyanobacterial blooms and freshwater salinization have recently received much attention, however, the comprehensive effects of these stressors on aquatic organisms are complex and have yet to be accurately clarified. This study tested the harmful effects of cyanobacteria and increasing salinity on zooplankton by characterizing the life-history traits and gut microbiota composition in the large-bodied Daphnia pulex and small-bodied Simocephalus vetulus. In 0 g L-1 salinity, the intrinsic growth rates of both species decreased when fed a diet containing cyanobacteria. Without cyanobacteria, the intrinsic growth rate of D. pulex was highest at 1 g L-1 salinity and lowest at 2 g L-1, whereas that of S. vetulus declined as salinity levels rose. Salinity alleviated the negative effects of cyanobacteria on water fleas. D. pulex performed worse than S. vetulus under high salinity (2 g L-1), cyanobacteria or their combined effects. Salinity changed the dominant gut microbiota in the water fleas when fed cyanobacteria. Bacteroides sp. and Cetobacterium sp. in D. pulex and Cetobacterium sp. in S. vetulus were most abundant when the water fleas were reared at low salinity (1 g L-1). The consistent changes in the dominant bacterial groups and the life-history traits indicate that the gut microbiota might adjust their tolerance to cyanobacteria.

Biogenic emission as a potential source of atmospheric aromatic hydrocarbons: Insights from a cyanobacterial bloom-occurring eutrophic lake

As important precursors of ozone (O3) and secondary organic aerosol (SOA), reactive aromatic hydrocarbons (AHs) have typically been classified as anthropogenic air pollutants. However, biogenic emission can also be a potential source of atmospheric AHs. Herein, field observations in a eutrophic lake were combined with laboratory incubation experiments to investigate the biogenic AH emission. Field work showed that the water-air fluxes of AHs measured at sites with high cyanobacteria abundance could reach an order of magnitude greater than those at sites with low cyanobacteria abundance, suggesting that cyanobacteria could be the important contributor to measured AHs. Laboratory incubation experiments further confirmed the AH emission of cyanobacteria and revealed that the emission could change significantly over the lifespan of cyanobacteria and varied to their growing conditions. By combining field observations and laboratory incubation experiments, it has been suggested that the emission of different AH species from cyanobacteria could be modulated by variable biogeochemical mechanisms and that the biochemical process of toluene could be different from that of other AHs. This study investigates AH emissions from inland aquatic ecosystem and suggests that biogenic emission could be a potential source of atmospheric AHs.

Metagenomic insights into cyanotoxin dynamics in a Mexican subtropical lake

Valle de Bravo is a vital water supply for part of the metropolitan area of the Valle de Mexico megacity, providing 30% of Mexico City's water demand. This water body has experienced an acceleration in its trophic status, going from oligotrophic to eutrophic in just a few years. This temperate lake (at a tropical latitude) is in a persistent bloom dominated by a variety of co-occurring cyanobacteria, many of which have toxigenic potential based on microscopic identification, that makes it difficult or even impractical to identify the cyanotoxin producers. To unravel this complexity and directly identify the toxigenic genera, we showed that integrating classical approaches with metagenomic is required. We first characterized, from genes to metagenomes assembled genomes, the toxigenic Cyanobacteria. We found that Microcystis was the most dominant cyanobacterial genus and the sole carrier of the mcy operon, making it the only microcystin producer. We then quantified twenty-one different cyanopeptides, including twelve microcystin congeners using a high-performance liquid chromatography-high-resolution. Nine microcystins (MCs) and the emerging cyanotoxin anabaenopeptin-A and -B were found at varying concentrations throughout the year, with MC-LA being the most common and abundant. Our findings, constrained by our sampling strategy, indicate that conventional cyanotoxin biomarkers (e.g., toxin mcy genes) were not consistently reliable indicators of cyanotoxin concentrations in this freshwater system. In this study, we followed the dynamics of the cyanobacterial community and the associated cyanopeptides with unprecedented resolution. Our results have implications for better management of toxic blooms in this freshwater system, which supplies drinking water to more than 7 million people in the megalopolis of Valle de México.

Metal Nanoparticles Produced Using Autotrophs and Their Bioproducts: A Comparative Overview between Photosynthesizing Taxonomic Groups

Metal nanoparticles (MNPs) exhibit unique properties influenced by their size, shape, and dispersion uniformity. They can be synthesized via chemical methods or green synthesis, commonly using plant or microorganism extracts as reducing and stabilizing agents. This eco-friendly approach is valued, but the literature is unclear about which taxonomic groups should be targeted to obtain certain types of MNPs. Given the ongoing growth of research in this area, this study offers a comparative overview that helps identify patterns and gaps in the current knowledge. This study reviewed 485 articles, describing 652 monometallic and 10 bimetallic nanoparticles synthesized using photosynthesizing organisms' extracts. Angiosperms and cyanobacteria were the most utilized groups. Silver and gold nanoparticles were the most studied MNPs. Gold nanoparticles' size varied with taxonomic groups, but they were smaller than the silver nanoparticles synthesized by the same group. Antimicrobial activity was the most common application, highlighting the potential of green-synthesized MNPs. This study provides valuable insights for optimizing sustainable nanoparticle production since knowledge about the specificities of different photosynthesizing taxa can be useful for directing efforts and enhancing the efficiency and precision of green-synthesized MNPs.

Influence of bloom stage on the effectiveness of algicidal bacteria in controlling harmful cyanobacteria: A microcosm study

Cyanobacterial harmful algae blooms (cyanoHABs) pose significant ecological and public health concerns in freshwater ecosystems worldwide. Understanding the dynamics of phytoplankton communities and the efficacy of mitigation strategies is crucial for managing bloom events. This study investigates the impact of bioaugmentation with algicidal bacteria on Microcystis-dominated blooms through laboratory microcosm experiments. Field-collected samples from MID- and POST-summer bloom stages were treated with Morganella morganii, Exiguobacterium acetylicum, and a bacterial consortium including Bacillus pumilus. Phytoplankton composition, microcystin concentrations and genes related to microbial community dynamics (16S, mcyA, nosZ and amoA) were assessed by microscopy, HPLC and qPCR, respectively. Results showed that M. morganii significantly altered the phytoplankton community structure and promoted diatom proliferation in MID-summer microcosms, though treatments were less effective in POST-summer microcosms representing more mature bloom periods. Additionally, algicidal bacteria influenced microcystin levels, with M. morganii and E. acetylicum reducing toxigenic Microcystis genotypes, as indicated by lower mcyA gene copy numbers. Molecular analyses also revealed that algicidal bacterial treatments contributed to shifts in microbial functional genes, including increased denitrification activity linked to nosZ gene abundance. These findings highlight the intricate interplay between algicidal bacteria and microbial communities, where algicidal activity extends beyond direct cyanobacteria suppression to broader ecosystem-level effects. By rebalancing phytoplankton communities toward eukaryotic dominance and reducing toxigenic cyanobacterial genotypes during intense bloom episodes, bioaugmentation with algicidal bacteria emerges as a promising strategy for bloom management and ecosystem restoration.

Development of a novel in-sediment passive sampler for profiling orthophosphate and internal phosphorus release near the sediment-water interface in a eutrophic lake

Internal phosphorus (P) release from lake sediments is now recognized as an important P supply that maintains eutrophication, especially in lakes where stratification induces hypoxic conditions in the bottom waters. Freshwater lakes are increasingly threatened by eutrophication and harmful algal blooms. Therefore, to manage lakes, it is important to quantify the internal P release. The internal flux of P (i.e., the orthophosphate (PO4) released from the sediments) may be miscalculated by the methods used to date, such as sediment core samples because the concentrations may be affected when the sediment is disturbed, and the spatial resolution of the sampling may be low. In this study, we developed a novel in-sediment passive sampler to determine the PO4 flux from sediment and deployed it in a eutrophic lake, Lake Barato in Sapporo, Japan. We also deployed Chemcatcher passive samplers for PO4 at the same time to investigate the change in the PO4 concentrations in the water column. With these methods, we obtained the vertical and horizontal distributions of the PO4 concentrations in the sediment porewater across approximately 10 × 20 cm close to the sediment-water interface (SWI) and in the water column. We observed relatively large centimeter-scale PO4 hotspots within the shallow sediment layers (-1 to -5 cm below the SWI). These PO4 hotspots were significantly larger during the summer season than in the other seasons, when thermal stratification and hypoxia influenced the P release. The PO4 fluxes calculated with data from the in-sediment passive samplers ranged from 0.05 to 0.37 mg-P/m2/d, and were considerably lower than the estimates from the conventional sediment core sampling methods. In addition, the data from the Chemcatcher passive samplers showed that the temporal patterns in the time-weighted average PO4 concentrations (around 10 µg-P/L) in the water column were consistent with the patterns from the in-sediment sampler. The results suggest that the in-sediment sampler provided a high-resolution vertical profile of the PO4 concentrations near the SWI with minimal sediment disturbance, and that passive sampling techniques could be used to monitor the fluxes of PO4 released from sediments and the PO4 concentrations in the water column.

Mitomycin C eliminates cyanobacterial transcription without detectable prophage induction in a Microcystis-dominated harmful algal bloom in Lake Erie

Although evidence indicates that viruses are important in the ecology of Microcystis spp., many questions remain. For example, how does Microcystis exist at high, bloom-associated cell concentrations in the presence of viruses that infect it? The phenomenon of lysogeny and associated homoimmunity offer possible explanations for this question. Virtually nothing is known about lysogeny in Microcystis, but a metatranscriptomic study suggests that widespread, transient lysogeny is active during blooms. These observations lead us to posit that lysogeny is important in modulating Microcystis blooms. Using a classic mitomycin C-based induction study, we tested for lysogeny in a Microcystis-dominated community in Lake Erie in 2019. Treated communities were incubated with 1 mg L-1 mitomycin C for 48 h alongside unamended controls. We compared direct counts of virus-like particles (VLPs) and examined community transcription for active infection by cyanophage. Mitomycin C treatment did not increase VLP count. Mitomycin C effectively eliminated transcription in the cyanobacterial community, while we detected no evidence of induction. Metatranscriptomic analysis demonstrated that the standard protocol of 1 mg L-1 was highly toxic to the cyanobacterial population, which likely inhibited induction of any prophage present. Follow-up lab studies indicated that 0.1 mg L-1 may be more appropriate for use in freshwater cyanobacterial studies. These findings will guide future efforts to detect lysogeny in Microcystis blooms.IMPORTANCEHarmful algal blooms dominated by Microcystis spp. occur throughout the world's freshwater ecosystems, leading to detrimental effects on ecosystem services that are well documented. After decades of research, the scientific community continues to struggle to understand the ecology of Microcystis blooms. The phenomenon of lysogeny offers an attractive potential explanation for several ecological questions surrounding blooms. However, almost nothing is known about lysogeny in Microcystis. We attempted to investigate lysogeny in a Microcystis bloom in Lake Erie and found that the standard protocols used to study lysogeny in aquatic communities are inappropriate for use in Microcystis studies, and perhaps freshwater cyanobacterial studies more broadly. This work can be used to design better methods to study the viral ecology of Microcystis blooms.

Planktonic communities as indicators of water quality in a tropical reservoir

Surface water bodies have been significantly altered by various human activities in the watersheds. Assessing these ecosystems is crucial for maintaining an ecological balance and protecting public health. This study aimed to analyse the water quality of a tropical public supply reservoir by evaluating the dynamics of planktonic communities. A total of 69 water quality parameters, in addition to phytoplankton and zooplankton biomonitoring data, were analyzed between 1989 and 2020. Preliminary and descriptive statistical analysis, trophic state index, Shannon-Wiener diversity index, statistical tests, and multivariate statistics analysis were applied. The results showed a change in the composition of the planktonic communities over time, with a greater abundance of cyanobacteria and an increase in the density of the Crustacea class in the final years of monitoring, indicating a more degraded environment. There was a reduction in the diversity of phytoplankton species. However, the concentrations of physical and chemical parameters remained low over the years, and oligotrophic conditions were prevalent in the reservoir. Therefore, the analysis of bioindicators provided information that was not observed when the physical and chemical parameters of water quality were analyzed. Possibly due to environmental variables not considered in this study, or due to the cumulative or synergistic effects caused by changes in the environment. It is evident that integrating bioassessment into the monitoring of water bodies is essential for a comprehensive ecological classification and for maintaining the integrity of the ecosystem.

Structural insights into the catalytic mechanism of the microcystin tailoring enzyme McyI

The most common cyanotoxin microcystin is a cyclic heptapeptide produced by non-ribosomal peptide-polyketide synthetases and tailoring enzymes. The tailoring enzyme McyI, a 2-hydroxyacid dehydrogenase, converts (3-methyl)malate into (3-methyl)oxaloacetate to produce the non-proteinogenic amino acid (3-methyl)aspartate. The reaction is NAD(P)-dependent but the catalytic mechanism remains unclear. Here we describe the crystal structures of McyI at three states: bound with copurified NAD, cocrystallized with NAD/NADP, and cocrystallized with malate or the substrate analogue citrate. An McyI protomer has unusual three nicotinamide cofactor-binding sites, named the NAD-prebound, NADP specific, and non-specific sites. Biochemical studies confirmed the NADP preference during oxidoreductase reaction. Molecular basis for McyI catalysis was revealed by the structures of McyI-NAD binary complex, McyI-NAD-NADP and McyI-NAD-malate ternary complexes, which demonstrate different opening angles between the substrate-binding domain and the nucleotide-binding domain. These findings indicate that McyI is a unique member of the 2-hydroxyacid dehydrogenase superfamily and provide detailed structural insights into its catalytic mechanism. In addition, the structural ensemble representing various binding states offers clues for designing enzyme for bioengineering applications.

Intelligent Detection and Recognition of Marine Plankton by Digital Holography and Deep Learning

The detection, observation, recognition, and statistics of marine plankton are the basis of marine ecological research. In recent years, digital holography has been widely applied to plankton detection and recognition. However, the recording and reconstruction of digital holography require a strictly controlled laboratory environment and time-consuming iterative computation, respectively, which impede its application in marine plankton imaging. In this paper, an intelligent method designed with digital holography and deep learning algorithms is proposed to detect and recognize marine plankton (IDRMP). An accurate integrated A-Unet network is established under the principle of deep learning and trained by digital holograms recorded with publicly available plankton datasets. This method can complete the work of reconstructing and recognizing a variety of plankton organisms stably and efficiently by a single hologram, and a system interface of YOLOv5 that can realize the task of the end-to-end detection of plankton by a single frame is provided. The structural similarities of the images reconstructed by IDRMP are all higher than 0.97, and the average accuracy of the detection of four plankton species, namely, Appendicularian, Chaetognath, Echinoderm and Hydromedusae,, reaches 91.0% after using YOLOv5. In optical experiments, typical marine plankton collected from Weifang, China, are employed as samples. For randomly selected samples of Copepods, Tunicates and Polychaetes, the results are ideal and acceptable, and a batch detection function is developed for the learning of the system. Our test and experiment results demonstrate that this method is efficient and accurate for the detection and recognition of numerous plankton within a certain volume of space after they are recorded by digital holography.

Spatial multi-omics analysis of metabolic heterogeneity in zebrafish exposed to microcystin-LR and its disinfection byproducts

Most studies on the biological effects of exogenous pollutants have focused on whole samples or cell populations, and lack spatial heterogeneity consideration due to technical limitations. Microcystin-LR (MC-LR) from cyanobacterial blooms threatens ecosystems and human health, while microcystin-LR disinfection by-products (MCLR-DBPs) in drinking water remain a concern for their toxin-like structure. This study introduces spatial multi-omics to investigate the disruptions caused by ingestion of MC-LR and MCLR-DBPs in zebrafish. The method integrates metabolomics, spatial metabolomics, and spatial transcriptomics to characterize the overall metabolic changes in whole zebrafish caused by MC-LR and MCLR-DBPs, then provides further insight into the variation of spatial distribution of metabolites and genes in MC-LR and MCLR-DBPs targeted organ. The results showed that MC-LR and MCLR-DBPs induced oxidative stress and metabolic imbalance, and disrupted the physiological homeostasis of zebrafish. Spatial multi-omics analysis further revealed that MC-LR and MCLR-DBPs exacerbate disruptions in energy and lipid metabolism, methylation processes, and immune pathways by modulating the expression of genes such as gatm, gnmt, cyp2p9, and tdo2b. In conclusion, this study developed a spatial multi-omics approach that not only enhances the understanding of the biological effects of MC-LR and MCLR-DBPs but also provides robust technical support for investigating other environmental pollutants.

Long-term suppression of Microcystis aeruginosa by tannic acid: Risks of microcystin pollution and proteomic mechanisms

Harmful algal blooms are a critical eco-environmental issue with severe impacts on aquatic ecosystems and human health. Tannic acid (TA) has been suggested as an effective algal bloom control, but the molecular mechanisms of its interaction with algae cells and its effects on algal toxin release remain unclear. This study tracked toxin production and release in the toxigenic species Microcystis aeruginosa (M. aeruginosa) exposed to TA, revealing underlying mechanisms through proteomic analysis. High TA doses effectively inhibited M. aeruginosa growth and microcystin-leucine-arginine (MC-LR) production. However, at a specific TA concentration, M. aeruginosa produced and released more MCs, with extracellular MC-LR levels peaking at 1.91 times the control on day 15. Proteomic analysis indicated upregulation of proteins related to the tricarboxylic acid (TCA) cycle, glycolysis, and leucine and arginine biosynthesis, suggesting a compensatory response in M. aeruginosa under TA stress that enhanced cellular energy supply and MC-LR biosynthesis. In addition, TA exposure significantly downregulated proteins involved in ion and metal-cluster binding, disrupting electron transfer and photosynthesis. This study provides new insights into TA-induced MC-pollution risks and TA's mechanisms in algae suppression, offering guidance for its application in algal bloom control.

Effect of chronic low-dose microcystin-LR exposure on jejunum apoptosis via RAF/ERK signaling pathway in mouse

Microcystin-LR (MC-LR), a class of cyclic heptapeptide compounds synthesized by cyanobacterial species, presents a significant risk to ecological systems and public health. Exposure to MC-LR was found to induce damage to various organs. One of the target organ systems affected by MC-LR is the gastrointestinal tract (GIT). However, the majority of studies regarding GIT focused on colorectal toxicity, with little attention paid to small intestinal toxic injuries, in particular jejunum. Thus, the aim of this study was to investigate the effects attributed to MC-LR exposure on apoptosis and underlying mechanisms utilizing a mouse jejunum injury model following chronic low-dose MC-LR treatment. A total of 40 C57BL/6 male mice were randomly divided into 4 groups with each group receiving drinking water containing 0, 1, 60, or 120 µg/L MC-LR for a duration of 12 months. Results indicated that exposure to MC-LR induced pathological alterations in jejunal tissue as evidenced by abnormal villous serration, crypt disorganization, and lymphocyte infiltration. TUNEL assays demonstrated a significant increase in apoptotic cell count in the 60 and 120 µg/L groups. The 60 and 120 µg/L MC-LR treatment groups exhibited elevated mRNA expression of Bax accompanied by significant reduction in mRNA expression of Bcl-2. The protein levels of cleaved caspase-3 were markedly elevated in the 60 and 120 µg/L MC-LR groups. The protein expression levels of p-RAF and p-ERK were significantly increased in the 60 and 120 µg/L MC-LR treatment groups. Data demonstrated suggest that the RAF/ERK signaling pathway may be involved in MC-LR- induced jejunal apoptosis.

World's largest oligotrophic Lake Baikal: Concerns about cyanobacterial blooms and potential microcystin producers along the littoral zone

Toxic cyanobacterial blooms are great challenge for water safety globally. Previous studies mainly focused on this issue in eutrophic lakes, but associated knowledge in oligotrophic lakes is quite scarce. Lake Baikal is the world's largest oligotrophic lake, containing about 20 % of world's available freshwater. In this study, sites grouped in the east (E1-E2), west (W1-W6), and southwest (SW1-SW3) located in the littoral zone of Lake Baikal, were sampled. The target genes of 16S rRNA and mcyE in cyanobacteria, potential microcystin producers, microcystin-producing Microcystis and Dolichospermum, were quantitatively detected in collected surface water samples, and the highest target gene abundance was observed at the site where the highest water temperature (WT) and total nitrogen (TN) were recorded (P<0.05). The WT showed a strong positive correlation with the target gene abundance, possibly via promoting the growth of cyanobacteria, potential microcystin producers or toxic strain proportion. The strong positive correlation between TN and absolute mcyE gene abundance of potential microcystin producers was also shown, and it was likely that its production is related to N availability. These findings suggested that the potential risk of cyanobacterial blooms and microcystin producers for water safety should not be ignored in the world's largest oligotrophic Lake Baikal, and WT and TN could be as pivotal factors to affect the potential risk. Consequently, it is vitally necessary for water authorities to take suitable action to cope with this challenge in hot spot littoral region of increased water temperature and nitrogen in a large oligotrophic lake.

Extra peptidase of a cyanophage confers its stronger lytic effect on bloom-forming Microcystis aeruginosa

Microcystis covers important cyanobacteria species that causes harmful algal blooms. Cyanophages are viruses that infect and lyse cyanobacteria and have been considered as potential cyanobacteria control strategy. Present study isolated two cyanophage strains, MaMV-CH01 (CH01) and MaMV-CH02 (CH02), infecting M. aeruginosa. Growth curves showed that CH01 has a stronger proliferation ability and host cell lysis capability than CH02. Combined with genomic, gene structure and function analysis, as well as biologic testing including infectivity, we confirmed that there is widespread horizontal gene transfer between the cyanophages and cyanobacteria, enabling the cyanophages to carry a series of auxiliary metabolic genes (AMG) related to host's metabolism. Moreover, compared with CH02, the cyanophage CH01 carrying extra AMG, a peptidase encoding gene (82R), exhibited stronger lytic activity against its host. Expression of CH01 82R in vitro showed strong bacteriostatic activity. Further, testing the cyanophage's ability to form plaques showed that the CH01(AMG+), which encodes the aforementioned peptidase, can form larger plaques, with an area of about threefold than that formed by CH02(AMG-). Above results indicated that the cyanophages with specific peptidase possessed stronger algicidal efficiency, which provided a direction for finding efficient cyanophages to regulate the population of bloom-forming cyanobacteria.

Environmental-level antibiotics disrupt Microcystis stoichiometry: An overlooked risk in the context of cyanobacterial harmful algal blooms

At trace levels (nanograms to micrograms per liter, ng L-1 - μg L-1), antibiotics exert stimulatory effects on cyanobacteria, potentially posing a threat to aquatic ecosystems. Here, environmentally relevant concentrations of antibiotics were firstly observed to disrupt the stoichiometry of cyanobacterium Microcystis (i.e., the quota and allocation patterns of carbon (C), nitrogen (N), and phosphorus (P)). In scenarios where the doses of antibiotics ranged from 50 to 200 ng L-1, cyanobacteria displayed a complex response - a reduction of their intracellular P pools by 22% to 24% and an adjustment of elemental allocation patterns, such as by a 51% increase in the ratio of C:P. Furthermore, at these doses, antibiotics significantly impacted the physiology of cyanobacteria, resulting in increased production of extracellular polymeric substances (EPS), a substantial rise in maximum biomass (169% to 219% increase), and an enlargement of colony size (22% to 37% increase). Transcriptomic analyses revealed that these changes were linked to the downregulation of ABC transporters and the upregulation of photosynthetic and ribosomal processes. This research offers novel insights into the hormesis effects on cyanobacteria and bloom formation, highlighting the necessity of using a multidimensional evaluation framework that integrates comprehensive bloom factors (biomass, colony size, and EPS) and elemental profiles (C, N, and P quotas and ratios) for accurate assessment.

Unraveling the mechanisms underlying the fluorescent probe detection of microcystin-LR and its binding with CT-DNA

Cyanobacteria blooms are concerning due to algal toxins like microcystin-leucine arginine (MC-LR). Despite progress in detecting MC-LR and understanding its toxic effects, including calf thymus DNA (CT-DNA) damage, the mechanisms for fluorescent probe detection of MC-LR and its binding to CT-DNA are poorly understood. In this study, we designed three fluorescent probes for MC-LR detection. Probe 1, with an acidic recognition site, is effective but influenced by solution pH. Probe 2, featuring a benzene ring structure, shows stable detection regardless of pH. Probe 3 offers the best performance, combining a long-chain and benzene ring structure. This suggests that combining these structures is beneficial for MC-LR probe design. Using Probe 3, we observed a strong interaction between MC-LR and CT-DNA. UV absorption spectroscopy, circular dichroism (CD) spectra, and molecular docking techniques provided the first evidence of MC-LR binding to CT-DNA through intercalation, with a binding saturation value of 8.33, significantly impacting CT-DNA structure. This study introduces a novel strategy for designing fluorescent probes for MC-LR detection, along with new insights into the interactions between MC-LR and CT-DNA.

Dynamics of Phytoplankton Communities and Their Characteristics of Realized Niches in a Drinking Reservoir

Realized niches are crucial in defining their optimal conditions and serve as valuable tools for predicting the phytoplankton dynamics in relation to eutrophication, climate change, and harmful phytoplankton blooms. However, previous studies have largely focused on marine ecosystems, leaving freshwater systems less studied. In this study, we elucidate the patterns of phytoplankton community succession based on their niche characteristics in the Shanmei (SM) Reservoir, a drinking water source in Quanzhou, Fujian Province. Additionally, variations in phytoplankton were mainly explained by their realized niche. In the SM Reservoir, total chlorophyll a concentrations ranged from 252 to 24,008 ng/L. The phytoplankton community was dominated by Chlorophyta and Cyanophyta, which consisted mostly of Pseudanabaena and Microcystis, especially in summer. This dominance was attributed to their wide niche breadth and high mean niche for temperature, nitrogen, and dissolved reactive phosphorus. On the other hand, Cryptophyta and Bacillariophyta reached higher concentrations in autumn and winter, linked to their low mean temperature niches. Under the multiple pressures of climate change and anthropogenic activities, Chlorophyta and Cyanophyta are likely to thrive in environments characterized by rising water temperatures and elevated nutrient concentrations. This is particularly true for buoyant cyanobacteria such as Pseudanabaena, which are well-suited to the stratified water layers induced by higher water temperatures. Therefore, incorporating niche characteristics of harmful bloom-forming species would contribute to the prevention and management of harmful phytoplankton blooms, ultimately improving the safety of drinking water.

Growth and anatoxin-a production of Microcoleus (Cyanobacteria) strains from streams in California, USA

Benthic cyanobacterial proliferations are an emerging concern globally due to their potential for toxin production and subsequent negative environmental and health impacts. Microcoleus is a common mat-forming genus reported to produce potent neurotoxin, anatoxin-a, ingestion of which has been associated with animal mortalities. Six different unialgal monoclonal strains of Microcoleus were isolated from streams in California and grown in batch culture for 49 days. The four toxic strains were identified using a polyphasic approach as belonging to the species Microcoleus anatoxicus, which expands its known distribution throughout the Klamath River and Rock Creek watersheds in northern California. The non-toxic strains from the Eel River belonged to Microcoleus sp. 1. Maximum toxin production occurred during the exponential growth phase, and peaked 6-13 days later in more toxic strains, with a persistently higher fraction of extracellular toxins compared to less toxic strains, which had maximum toxin concentrations at day 13. The proposed mechanism of toxin release into culture medium was through damage to the cell walls of unhealthy filaments. Peak toxin production was energetically expensive for all M. anatoxicus strains, evidenced by reduced specific growth rates at the time of peak toxin production, followed by quick recovery of cell division. Despite this, more toxic strains achieved faster maximum growth rates than the less toxic and non-toxic strains under luxurious nutrient culture conditions. Differential toxin and growth rate responses of M. anatoxicus strains from wide geographical ranges under the same laboratory-controlled conditions suggest high intraspecific variation, which may represent challenges for harmful algal blooms mitigation. More toxic strains have the potential to proliferate and consistently release extracellular anatoxins into the environment. This study provides a baseline to understanding the growth and toxin kinetics of two commonly occurring Microcoleus species in northern California which may help benthic harmful cyanobacteria management.

Structure and function analysis of microcystin transport protein MlrD

Microorganisms play a crucial role in the degradation of microcystins (MCs), with most MC-degrading bacteria utilizing the mlr gene cluster (mlrABCD) mechanism. While previous studies have advanced our understanding of the structure, function, and degradation mechanisms of MlrA, MlrB, and MlrC, research on MlrD remains limited. Consequently, the molecular structure and specific catalytic processes of MlrD are still unclear. This study investigates MlrD from Sphingopyxis sp. USTB-05, utilizing bioinformatics tools for analysis and prediction, conducting homology analysis, and constructing the molecular structure of MlrD. Bioinformatics analysis suggests that MlrD is an alkaline, hydrophobic protein with good thermal stability and is likely located in the cell membrane as a membrane protein without a signal peptide. Homology analysis indicates that MlrD belongs to the PTR2 protein family and contains a PTR2 domain. Phylogenetic analysis reveals that MlrD follows both vertical and horizontal genetic transfer patterns during evolution. Homology modeling demonstrates that the three-dimensional structure of MlrD is primarily composed of 12 α-helices, with conserved residues between the N-terminal and C-terminal domains forming a large reaction cavity. This research broadens current knowledge of MC biodegradation and offers a promising foundation for future studies.

A comparative analysis of data-driven modeling approaches to forecast cyanobacteria algal blooms in eutrophic lake discharge canals

This study explored the use of data-driven models to develop management-oriented prediction tools for algae blooms (ABs) represented by Chlorophyll-A (Chla) concentrations, using the Caloosahatchee and St. Lucie canals in Lake Okeechobee, Florida, as case studies. By comparing two modeling approaches, i.e., cascading modeling and time-lag modeling, the study aims to understand the differences in Chla dynamics between the two canals, identify the main drivers and predictors of Chla concentration in each, and develop suitable forecasting models for the canals' operation purposes. Throughout this study, both approaches demonstrated their value in improving the understanding of water quality dynamics in Lake Okeechobee canals. While some water quality parameters such as Dissolved Oxygen (DO) and Nitrate-Nitrite (NOx) were critical to ABs in the Caloosahatchee and St. Lucie canals, respectively, the effect of operation decisions on ABs was more significant on the St. Lucie than on the Caloosahatchee. From a modeling perspective, the time-lag modeling approach achieved higher predictive accuracy for Chla concentrations in both Caloosahatchee and St. Lucie canals. Particularly, at station S80 of St. Lucie canal, the XGBoost (XGB) algorithm achieved R2= 99% and RMSE = 0.001 μg/l in training, and R2= 60.1% and RMSE = 4.58 μg/l in testing. At station S79 of Caloosahatchee canal, Random Forest (RF) appeared to be the best model with R2= 85.7% and RMSE = 5.63 μg/l in training, and R2= 39% with RMSE = 10.06 μg/l in testing. In this study, the time-lag modeling approach was proven to offer decision-makers flexible tools for implementing better management strategies based solely on operation decisions and meteorological conditions.

Unexpected cyanobacterial communities in highly heterogeneous toxic blooms from a Mediterranean protected area

The negative effects associated with cyanobacterial blooms are of particular concern in protected ecosystems, as these areas are ecologically significant and attract a high number of visitors. This study aims to explore the cyanobacterial communities and associated toxicity in three reservoirs located within a Mediterranean National Park with a compromised situation at basin-level. Our results demonstrate the occurrence of dense toxic blooms containing microcystins (reaching values close to 280 μg L-1) and low levels of anatoxin-a and saxitoxins (up to 0.02 μg L-1). Comprehensive metabarcoding analyses based on cyanobacterial 16S rRNA and cyanotoxin-biosynthesis genes (mcyE, anaF and sxtA) unveiled three highly heterogeneous communities, despite the spatial proximity of reservoirs. Additionally, our results suggested the influence of water conductivity on the blooms composition. Among the diverse bloom-forming taxa found, Microcystis sp. and Planktothrix sp. were revealed as the microcystins-producer candidates, and Cuspidothrix issatschenkoi and Dolichospermum/Aphanizomenom sp. as the potential producers of anatoxin-a and saxitoxins, respectively. A polyphasic characterization confirmed the first report of the tropical-related species Planktothrix spiroides in Europe, showing elevated level of dominance. As a whole, we present the scenario of an ecologically important protected area facing significant challenges in the proper management of cyanobacterial blooms.

Seasonal dynamics and factors shaping microbiomes in freshwater finfish earthen aquaculture ponds in Bangladesh

BACKGROUND

The pondwater microbiome is believed to play a key role in fish health, including shaping mucosal surface microbiomes that help to protect against disease. How different physiochemical features relating to season, geographical locations, as well as crop species shape the pond water microbiome in the finfish aquaculture system, is not well established. Pangasius (Pangasianodon hypophthalmus) and tilapia (Oreochromis niloticus) are two of the most widely farmed fish species and disease is a major impediment to the expansion of their production. We applied 16S and 18S rRNA metabarcoding to assess how pond physicochemistry and geographical location shape water microbiomes in pangasius and tilapia aquaculture earthen ponds in Bangladesh.

RESULTS

Planctomycetota, Pseudomonadota and Actinomycetota were the dominant bacterial phyla while Stramenopiles and Alveolata were the dominant microeukaryotes (divisions) in the pangasius and tilapia ponds water. The relative abundance of Planctomycetota was higher in the pangasius ponds compared with tilapia ponds, and Actinomycetota, and Pseudomonadota were relatively higher in tilapia ponds. Tilapia pond water also exhibited a higher microbial diversity compared to that in pangasius ponds. The pondwater microbial diversity was at its lowest in winter (and/or in monsoon) and highest in the pre-monsoon period. The microbial community structures differed across the different seasons, geographical locations, culture systems, and crop species, with season and geographical locations showing the strongest effects. Of the water physicochemistry features assessed, temperature and pH were found to have a weak but significant effect on the water microbiome content for both pangasius and tilapia ponds. Pangasius and tilapia ponds shared over 46% of ASVs, and around 30% of ASVs were shared across the different study geographical locations.

CONCLUSION

Our findings demonstrate that microbial communities in pangasius and tilapia aquaculture systems in Bangladesh are shaped by season, geographical location, crop species, as well as effects from water physicochemistry. Our results provide insights into the dynamic nature and environmental influences on water microbiomes that may be applied for use in pond management for improving aquaculture productivity and enhancement of overall fish health.

Testate amoebae are informative bioindicators of critically high ammonia deposition on peatlands

The global nitrogen cycle has been majorly disrupted by anthropogenic activity. While nitrogen emissions in the UK and Ireland are declining, ammonia (NH3) remains a significant exception. NH3 emissions are mostly agriculturally sourced and deposited on nearby habitats at high rates in both countries. Peatlands are globally important wetlands that are vulnerable to NH3 deposition. Essential peatland restoration risks being diminished by excessive NH3 deposition, leading to the loss of valuable ecosystem services. This study investigates testate amoebae (indicators of contemporary and historic peatland conditions) as bioindicators of seasonal NH3 deposition on six peatlands across Northern Ireland, UK. Sphagnum, an NH3-sensitive bryophyte, was sampled adjacent to NH3 monitoring sites once per season for a year. When NH3 deposition was critically high, multivariate analysis demonstrates a link between NH3 and testate amoebae assemblage change. Similarly, at high NH3 deposition sites, testate amoebae taxa diversity is observed to be significantly reduced in springtime, when it is expected to be highest. Although, in response to high NH3 deposition large algivorous taxa do not proliferate as was anticipated, and mixotrophic taxa abundance decreases could not be linked primarily to NH3. This research demonstrates the continued potential of testate amoebae as highly informative peatland bioindicators.

Cyanobacterial blooms specifically alter the dispersal-mediated taxonomic and functional vertical similarity of microbial communities in a subtropical reservoir

Harmful cyanobacterial blooms, including Raphidiopsis raciborskii (basionym Cylindrospermopsis raciborskii), are an increasing environmental concern in freshwater ecosystems globally. However, the ecological consequences of cyanobacterial blooms for the vertical similarity of microbial community structure have yet to be thoroughly investigated, especially in deep waters. Here, we explored the taxonomic and functional similarity of microbial communities at different depths in a subtropical reservoir over a 7-year period following multiple R. raciborskii blooms. Our results showed that vertical microbial dispersal, rather than ecological niche, is the main process determining vertical similarity. Both particle-attached (PA) and free-living (FL) bacteria from the surface water were able to reach the deep water, particle size being a contributing factor to their vertical dispersal. Cyanobacterial blooms enhanced the vertical microbial transport of PA, impacting the composition and biogeochemical processes of deep microbial communities. During the mixing period, microbial taxonomic and functional similarities between the different water layers were high whereas they were minimal across the oxycline during the stratification period, suggesting a bottleneck in microbial vertical dispersal. In the deep water layers, the abundances of specific taxa, such as those of Burkholderiales and Desulfomonilales in PA and FL fractions respectively in stratification periods, increased during blooms. Additionally, cyanobacterial blooms enhanced sulfur compound respiration in both PA and FL fractions and suppressed nitrification in PA bacteria and denitrification in FL bacteria, simultaneously reducing light-utilization capacity in PA bacteria and altering organic matter degradation. Several mechanisms are proposed to drive variations in microbial vertical connectivity by cyanobacteria, including ecological niche shifts and alterations of physicochemical properties and nutrient dynamics. Overall, our results reveal complex effects of cyanobacterial blooms on microbial taxonomic and functional vertical similarity and highlight the contribution of surface communities to the biodiversity and biogeography of deep communities.

Development and validation of a multiclass LC-MS/MS method for the analysis of cyanotoxins

Cyanobacteria are prokaryotic organisms that can form large monospecific blooms, which pose a risk to human and animal health as some species produce toxic secondary metabolites called cyanotoxins. Multiclass cyanotoxin analysis is challenging due to varying chemical and physical properties between classes, as well as potentially large numbers of analogues within each class. Incorporating anatoxins (ATXs) into multiclass methods can be particularly challenging due to their small molecular size, potential interferences, polarity, and a lack of chemical standards for most analogues. Here, we present the development of a multiclass LC-MS/MS method and a quantitative calibration solution for aetokthonotoxin (AETX), an emerging cyanotoxin linked to mass mortalities of bald eagles in the Eastern United States. The developed method is capable of detecting 17 microcystins (MCs), nodularin-R, three cylindrospermopsins (CYNs), AETX, and 17 ATXs, including recently tentatively identified 10-hydroxy analogues. Analytes were identified by retention time and product ion ratio matching with available standards. The method was evaluated with respect to limits of detection (LODs), linear range, accuracy, and precision using neat and matrix matched standards. LODs in wet cyanobacterial biofilms ranged from 0.14 ng/g for CYN to 2.8 ng/g for [Dha7]MC-LR with accuracies ranging from 65% for [Leu1]MC-LY to 116% for CYN. Finally, the method's application was demonstrated through analysis of cyanobacterial field samples, a dietary supplement matrix reference material, and passive sampler extracts to assess versatility within different matrices.

Microcystin production is important for toxic Microcystis to survive long-term nitrogen starvation

Toxic cyanobacterial blooms have expanded and intensified on a global scale. Although microcystins are known as the most abundant cyanotoxins released during cyanobacterial blooms, the physiological role of these toxic secondary metabolites has not been fully resolved. Here, we show that microcystin production is important for toxic Microcystis to maintain carbon metabolism under long-term nitrogen starvation and subsequent recovery. Compared to carbon metabolism in the nonmicrocystin-producing strains, toxic Microcystis could accumulate more carbon reserves under nitrogen limitation, which is important for the survival of cells under stressful conditions. Transcriptomic analysis revealed that the genes involved in microcystin synthesis were significantly up-regulated at the initial recovery phase, indicating their essential role in strengthening glycogen catabolism and fueling recovery. Flow cytometry analysis showed that compared to nontoxic strains, microcystin-producing Microcystis exhibited a higher survival and recovery rate after prolonged nitrogen starvation, which is consistent with the dominance of these species at the early stage of cyanobacterial blooms. The close genetic traits between Microcystis strains suggest that the strategies observed here might be highly conserved. Our results imply that toxic Microcystis establishes a competitive advantage over nontoxic species and provides insights into the seasonal succession of natural Microcystis populations.

Utilization of Algal Biochar for Biopassivation of Copper Sulfide Tailings to Reduce Acid Mine Drainage

Acid mine drainage (AMD) has serious impacts on the environment. To inhibit the generation of AMD from copper sulfide tailings at the source, in this paper, a strategy is developed for promoting the biopassivation of copper sulfide tailings using algal biochar, and the effects of the pyrolysis temperature and concentration of algal biochar on the passivation efficiency and stability are investigated. The results reveal that the introduction of algal biochar during the biopassivation of copper sulfide tailings significantly enhances the tailings passivation effect of the tested Acidithiobacillus ferrooxidans strain and greatly stabilizes the formed passivation layer. Algal biochar prepared with a pyrolysis temperature of 300 °C and applied at a concentration of 6 g/L not only optimizes biopassivation but also significantly improves the stability of the passivation layer. The complex mechanisms of algal biochar in this system include regulating the pH and oxidation‒reduction potential of the reaction system, effectively adsorbing microbial cells, efficiently aggregating metal cations in solution, stimulating the synthesis of extracellular polymeric substances, and accelerating electron transfer. This research offers a novel method for the benign treatment of copper sulfide tailings and resource utilization of algae.

Diversity and Structure of the Prokaryotic Community in Tropical Monomictic Reservoir

Bacteria and Archaea are microorganisms that play key roles in the biogeochemical transformations that control water quality in freshwater ecosystems, such as in reservoirs. In this study, we characterize the prokaryotic community of a high-relevance tropical eutrophic reservoir using a 16S rRNA gene survey during a low-water level fluctuation period mainly used for storage, associating the distribution of these microorganisms with the hydrogeochemical conditions of the water column. Our findings revealed that diversity and structure of the prokaryotic community exhibited spatio-temporal variations driven by the annual circulation-stratification hydrodynamic cycle and are significantly correlated with the concentrations of dissolved oxygen (DO), soluble reactive phosphorus (SRP), and dissolved inorganic nitrogen (DIN). During the heterotrophic circulation, the breakdown of thermal gradient leads to a homogeneous distribution of the nutrients, where the presence of DO promotes the dominance of aerobic and facultative heterotrophic bacteria such as Bacteroidota, Actinobacteriota, and Verrucomicrobiota. Also, the autotrophic circulation was characterized by an increase of DO and NO3- concentrations, with abundant Cyanobacteria. Finally, during the stratification, the presence of prokaryotes associated with the metabolism of CH4 was detected, mainly in the hypolimnion, as well as others related to sulfate reduction and nitrification. This study shows the diversity of the prokaryotic community in tropical eutrophic reservoirs, and how the continuous monitoring with metabarcoding techniques can provide critical insights for a deeper understanding of the biogeochemical dynamics and improve the water resource management in the future.

Health and Environmental Impacts of Cyanobacteria and Cyanotoxins from Freshwater to Seawater

Cyanobacterial harmful algal blooms (cyanoHABs) are a natural phenomenon produced mainly by the interaction between natural and anthropogenic events. CyanoHABs are characterized by the production of cyanotoxins that can have harmful effects on different species within the food web and even affect human health. Among the most prevalent toxin groups worldwide are microcystins (MCs), anatoxins (ATXs), cylindrospermopsins (CYNs) and nodularins (NODs), which are characterized as toxins with hepatotoxic, neurotoxic, and cytotoxic effects. This review summarizes and analyzes research on the influence of cyanoHABs, the main toxin-producing cyanobacteria and the most prevalent cyanotoxins in freshwater and marine bodies, highlighting their global occurrence, toxicology, and bioaccumulation dynamics in vectors of the food web, and the main cases of acute and chronic intoxications in humans. This review is useful for understanding the dynamics of cyanoHABs' interaction with the ecosystem and their impact on human health, and how the implementation of a surveillance and management framework for cyanobacteria and cyanotoxins could generate vital information for stakeholders to establish health guidelines on the risks and hazards of cyanoHABs for the ecosystem and humans.

Dongting Lake algal bloom forecasting: Robustness and accuracy analysis of deep learning models

Harmful algal blooms (HABs) pose a significant threat to aquatic ecosystems, prompting efforts to predict their occurrence for swift action by water management agencies. Despite the potential for high-precision forecasting through machine learning, the effectiveness of these models is often compromised by data quality issues, such as incomplete data sets, inaccuracies in historical records, inconsistencies in sampling methods, and the dynamic nature of environmental factors, leading to temporal and spatial variability. This study develops an early warning system for HABs using water quality data from a freshwater lake prone to such blooms. It employs a deep learning approach that integrates time series analysis with the iTransformer model to enhance prediction accuracy. The methodology utilizes the iTransformer model's robust preprocessing capabilities to address missing values and maintain data continuity, ensuring effectiveness even when with incomplete datasets. Additionally, the study identifies key factors influencing algal density by analyzing the model's attention weights, highlighting the importance of nutrients and temperature. A feature ablation experiment underscores the model's inherent robustness, showcasing its ability to deliver reliable predictions despite incomplete data. The research contributes to water quality management in Dongting Lake and presents a novel application of deep learning in environmental monitoring. Despite the model's current effectiveness, future work should explore additional environmental variables to enhance its predictive power and generalizability.

Metatranscriptomics reveals gene expression dynamics during an anatoxin-a producing Dolichospermum bloom in a western coastal lake

Cyanobacteria harmful algal blooms in lakes are primarily driven by nutrient and temperature conditions, yet the interplay of these abiotic factors with microbial community dynamics during bloom events is complex and challenging to unravel. Despite advances through deep sequencing approaches, the underlying transcriptomic changes occurring within blooming and non-blooming taxa remains an actively expanding area of study. In this work, we examined a spring-summer bloom event in Anderson Lake, WA, which has experienced recurring annual blooms dominated by the filamentous, anatoxin-a producing, diazotroph: Dolichospermum sp. WA102. Our data reveal the overall transcriptional dominance by Dolichospermum sp. WA102 during the bloom, initiated with increasing temperature and light intensity under high available phosphorus but low nitrogen conditions. We find that heterocyst differentiation was already transcriptionally initiated prior to the bloom, facilitating downstream gene cascades necessary for rapid nitrogen fixation and metabolism. As the bloom progresses, phosphorus becomes depleted, necessitating the expression of Pho regulon components in Dolichospermum sp. WA102 and possibly curtailing the bloom itself. We dissect toxin production and the transcriptional subtleties of the anatoxin-a synthesis locus. Additionally, co-occurring taxa exhibited distinct gene expression profiles, with competition for nutrients, light, and potential allelopathic interactions acting as drivers. Overall, our data provide a unique transcriptomic perspective on a single-taxa-driven, anatoxin-producing bloom, highlighting its competitive adaptation to nutrient acquisition and favorable conditions. This deeper understanding of the genetic mechanisms underlying algal bloom events may aid in predicting and preventing future blooms.

Artificial destratification options for reservoir management

Reservoir stratification impacts reservoir and downstream water quality, creating complex management challenges driven by interactions between hydrodynamics, weather patterns, and nutrient dynamics. Artificial destratification is one technique used to ameliorate the impacts of stratified reservoirs, with bubble plumes or mechanical mixers being the primary methods employed. This global review assessed 138 bubble plume and mechanical mixer artificial destratification systems installed in 114 reservoirs to evaluate the comparative effectiveness of each method. Destratification systems were assessed in terms of their effectiveness in breaking thermal stratification and consequently mitigating cold water pollution, increasing dissolved oxygen concentrations throughout the water column, reducing the concentration of soluble metals, and reducing (potentially toxic) cyanobacteria populations. Bubble plume destratification was found to be more effective than mechanical mixing at mitigating the impacts of thermal stratification. Successful thermal destratification was closely linked to subsequent increases in dissolved oxygen concentrations and decreases in manganese and iron concentrations. Mixed results were observed for the reduction of cyanobacteria populations from artificial destratification; however, a correlation was observed between cyanobacteria control and successful thermal destratification in deeper reservoirs. Achieving thermal destratification was closely linked to the ratio of the reservoir capacity to the air flowrate used for destratification (the "volumetric destratification coefficient"). Failed thermal destratification was observed in reservoirs where the volumetric destratification coefficient was less than approximately 0.005 L/s/ML. This review identified the potential for scalability of bubble plume destratification across different reservoirs, but future research needs to provide more quantitative data that can be used to develop holistic design guidelines for bubble plume destratification systems for a wide range of reservoirs and operational conditions.

Record-setting cyanobacterial bloom in the largest freshwater lake in northern China caused by joint effects of hydrological variations and nutrient enrichment

Cyanobacterial blooms represent a significant environmental issue posing widespread threats to global aquatic ecological health. Climate and nutrient enrichment were the most studied factors modulating cyanobacterial blooms in eutrophic lakes. However, in many floodplain lakes, the importance of hydrological variation in driving and predicting cyanobacterial blooms is often overlooked and largely underestimated, which has hampered the effectiveness of lake management. Here, we use a process-based lake ecosystem model (GOTM-WET) to evaluate the potential drivers of the record-setting cyanobacterial bloom during summer 2022 (>70% of lake area) in the largest shallow lake in Northern China (Hulun Lake). The model was calibrated based on a comprehensive field dataset including both remote sensing (surface water temperature) and in-lake observations (water quality). We performed a scenario analysis with various combinations of nutrient loading, hydrological variations and climate change. Our modeling results unravel that the profound water level rise through 2021 to 2022 serves as the main trigger of the severe cyanobacterial bloom in summer 2022. Our model predicted a decrease of 60.5% in the annual average of cyanobacterial biomass when water level remained stable. In addition, water level change and nutrient concentration explains 72.5% of the variance in long-term maximum area of cyanobacterial blooms. Our model further reveals that the water level rise drives the cyanobacterial bloom via bringing in excessive nutrient to lake water column from the lake basin. Thus, our results suggest that continuous increase in water level across two years could serve as an early warning signal to cyanobacterial blooms in the consecutive summer. Our findings may be applicable to similar temperate shallow lakes in floodplain areas, especially for those located in agricultural and pasture regions with abundant nutrient legacy, thus may provide a new indicator for cyanobacterial blooms prediction.

Rainfall impacts on nonpoint nitrogen and phosphorus dynamics in an agricultural river in subtropical montane reservoir region of southeast China

The increased frequency and intensity of heavy rainfall events due to climate change could potentially influence the movement of nutrients from land-based regions into recipient rivers. However, little information is available on how the rainfall affect nutrient dynamics in subtropical montane rivers with complex land use. This study conducted high-frequency monitoring to study the effects of rainfall on nutrients dynamics in an agricultural river draining to Lake Qiandaohu, a montane reservoir of southeast China. The results showed that riverine total nitrogen (TN) and total phosphorus (TP) concentrations increased continuously with increasing rainfall intensity, while TN:TP decreased. The heavy rainfall and rainstorm drove more than 30% of the annual N and P loading in only 5.20% of the total rainfall period, indicating that increased storm runoff is likely to exacerbate eutrophication in montane reservoirs. NO3--N is the primary nitrogen form lost, while particulate phosphorus (PP) dominated phosphorus loss. The main source of N is cropland, and the main source of P is residential area. Spatially, forested watersheds have better drainage quality, while it is still a potential source of nonpoint pollution during rainfall events. TN and TP concentrations were significantly higher at sites dominated by cropland and residential area, indicating their substantial contributions to deteriorating river water quality. Temporally, TN and TP concentrations reached high values in May-August when rainfall was most intense, while they were lower in autumn and winter than that in spring and summer under the same rainfall intensities. The results emphasize the influence of rainfall-runoff and land use on dynamics of riverine N and P loads, providing guidance for nutrient load reduction planning for Lake Qiandaohu.

Climate change unveils hidden microbial dangers

Climate change is driving unprecedented transformations in aquatic ecosystems, where microorganisms play a fundamental role in maintaining ecological balance and human health security. Rising water temperatures, pollution intensification, and extreme weather events are driving significant shifts in microbial community structures. These changes facilitate the proliferation of pathogenic microorganisms such as Vibrio cholerae and harmful algae like cyanobacteria, which thrive in warmer, nutrient-enriched environments. The resulting harmful algal blooms release potent toxins, such as microcystins, that contaminate drinking water and food supplies, leading to severe health impacts, including liver diseases and carcinogenesis. Furthermore, antibiotic resistance genes are spreading more rapidly due to climate-induced stressors, increasing the prevalence of antimicrobial-resistant pathogens and compounding the challenges for global health systems. This discussion article demonstrates that climate change influences aquatic microbial ecosystems through interconnected mechanisms, including shifts in gene transfer networks, alterations in microbial metabolism, and ecological feedback loops, ultimately increasing waterborne disease risks and antimicrobial resistance. Specific solutions are proposed, such as advancing wastewater treatment technologies to address climate-induced pollution, establishing global microbial monitoring networks leveraging remote sensing and molecular tools, and implementing early warning systems for waterborne disease outbreaks. Additionally, the discussion article emphasizes the critical role of international cooperation in funding and capacity-building efforts, particularly in developing regions with fragile infrastructures. By highlighting these pressing challenges and proposing actionable strategies, this research underscores the urgent need for integrated approaches to safeguard water resources, mitigate microbial hazards, and enhance public health resilience in an era of accelerating climate change.

Higher sensitivity of microcystin-producing Microcystis to two algaecides compared to co-cultured non-microcystin producers

Targeting and selectivity are essential for assessing the effectiveness of ecofriendly algaecides in controlling toxic cyanobacterial blooms. The dose- and time-dependent effects of hydrogen peroxide (H2O2), pyrogallol and their sustained-release microcapsules (HRM, PRM) on proportion of MC-producing cell numbers and genotypes of the co-existing MC- and non-MC-producing Microcystis, as well as microcystins (MCs) concentrations were investigated in the present study. Two MC-producing and two non-MC-producing Microcystis strains were used in mono- and co-culture test systems. The findings revealed that the MC-producing Microcystis strains were more sensitive to both forms of H2O2 and pyrogallol in comparison with the non-MC-producing strains. Inhibition of all Microcystis strains by H2O2 and pyrogallol was found to be dose- and time-dependent, with H2O2 exhibiting stronger effects. Additionally, both pure and granular forms of H2O2 and pyrogallol reduced the relative abundance of MC-producing genotypes in co-culture conditions, along with total MC concentrations. The HRM and PRM demonstrated more potent and prolonged effects than their pure forms, indicating they are optimal for targeted reduction of Microcystis bloom toxicity. Their long-term effects against different levels of MC-producing Microcystis in various environmental conditions need further investigation through large-scale outdoor experiments.

Projected response of algal blooms in global lakes to future climatic and land use changes: Machine learning approaches

The eutrophication of lakes and the subsequent algal blooms have become significant environmental issues of global concern in recent years. With ongoing global warming and intensifying human activities, water quality trends in lakes worldwide varied significantly, and the trend of algal blooms in the next few decades is unclear. However, there is a lack of comprehensive quantitative research on the future projection of lake algal blooms globally due to the scarcity of long-term algal blooms observational data and the complex nonlinear relationships between algal blooms and their driving factors. We aimed to develop a global projection model to evaluate the future trend in algal bloom occurrences in large lakes under various socio-economic development scenarios. We focused our research on 161 natural lakes worldwide, each exceeding 500 km2. The results indicated that the Random Forest model performed best (Overall Accuracy: 0.9697, Kappa: 0.8721) among various machine learning models which were applied in this study. The predicted results showed that, by the end of this century, the number of lakes experiencing algal blooms and the intensity of these blooms will worsen under higher forcing scenarios (SSP370 and SSP585) (p < 0.05). In different regions, lakes with increasing algal blooms are mainly distributed in Africa, Asia, and North America, while lakes with decreasing occurrence are primarily found in Europe. Additionally, underdeveloped regions, such as Africa, exhibit greater sensitivity to different SSP scenarios due to high variability in population and economic growth. This study revealed the spatiotemporal distribution of algal blooms in global lakes from 2020 to 2100 and suggested that the intensifying algal blooms due to global warming and human activities may offset the effort of controlling the water quality.

Algaecidal effects of tryptoline, tryptamine, and other microbial metabolites on target and non-target freshwater cyanobacteria and freshwater indicator organisms

Cyanobacterial harmful algal blooms (cyanoHABs) are a growing global concern due to their negative impacts on freshwater lakes and river ecosystems. HABs impact local and regional economies by restricting fisheries resources, recreational and commercial waterways, and threatening drinking water sources. To control HABs, researchers are developing short- and long-term mitigation strategies by exploiting natural, bacterial-derived products as targeted chemical control reagents to reduce the severity of HABs. In this study, we characterized the cyanocidal and ecotoxicological properties of tryptoline, tryptamine, isatin and other commercially available, bacterially derived compounds against both lab-adapted and field collected freshwater cyanobacterial strains that collectively include genera from Microcystis, Umezakia, Raphidiopsis, Dolichospermum, Planktothrix, Vulcanococcus, Anabaena and Synechocystis. Initially, chemicals were assessed for their ability to control cyanobacteria by screening them on cyanobacteria lawn plates. Those chemicals that created zones of clearing underwent further testing through liquid assay studies, where biomass was monitored using chlorophyll extractions. Results indicate that tryptoline was the most effective chemical at all concentrations tested leading to a 52 % reduction in algal biomass and this was independent of initial algal biomass, whereas tryptamine reduced algal biomass by 25 % and was most effective at low to medium algal cell densities. In addition, tryptoline was more toxic to the cyanobacteria strains in both the single and repeated exposures compared to tryptamine due to its increased resistance to degradation compared to tryptamine which had degraded 27.9 % after 72 h. The acute and chronic toxicity studies using the standard non-target zooplankton Ceriodaphnia dubia and fish Pimephales promelas resulted in hazard values for tryptoline that indicate it could be difficult to achieve an acceptable margin of safety to avoid non-target species effects when using this chemical in a cyanoHAB treatment. In contrast, tryptamine was at least 2 times less toxic to both non-target species than trypoline (e.g., Pimephales promelas 96-hour LC50 for tryptamine was 26.97 mg/L compared to had an 96-hour LC50 of 2.9 mg/L for tryptoline). Results from these studies collectively provide further data on the feasibility of bacterial-derived algaecides with regards to multi-treatment regimens and optimal cyanobacterial bloom densities. These studies also provide relevant non-target species testing and safety factors for those chemicals demonstrating the most effective algaecide activity.