Toxic benthic freshwater cyanobacterial proliferations: Challenges and solutions for enhancing knowledge and improving monitoring and mitigation

First report of PST-producing Microseira wollei from China reveals its novel toxin profile

Microseira wollei, a globally distributed freshwater bloom-forming benthic cyanobacterium, is known for its production of cyanotoxins and taste and odor (T&O). While CYN (Cylindrospermopsin)-producing populations of M. wollei are confined to Australia, PST (Paralytic shellfish toxins)-producing populations have been exclusively documented in North America. In this study, four benthic cyanobacterial strains, isolated from West Lake in China, were identified as M. wollei based on morphological and phylogenetic analyses. Detection of sxtA gene and UPLC-MS/MS analysis conclusively confirmed the PST-producing capability of M. wollei CHAB5998. In the phylogenetic tree of 16S rDNA, M. wollei strains formed a monophyletic group with two subclades. Notably, non-PST-producing Chinese strains clustered with Australian strains in Clade II, while all other strains, including PST-producing ones, clustered in Clade I. Additionally, CHAB5998 contains ten PST variants, of which STX, NEO, GTX2, GTX3, GTX5 and C1 were identified for the first time in M. wollei. Sequence analysis of PST biosynthetic gene cluster (sxt) genes indicated potential base variations, gene rearrangements, insertions, and deletions in the strain CHAB5998. Also, sxt gene has a longer evolutionary history in M. wollei than that in cyanobacteria from Nostocales. Multiple recombination breakpoints detected in sxt genes and the inconsistency in the topology of the phylogenetic trees between sxt and 16S rDNA suggested that multiple horizontal gene transfers (HGT) have occurred. Overall, the present study marks the first documented occurrence of PST-producing M. wollei outside of North America and identifies it as the first toxic freshwater benthic cyanobacterium in China. This revelation implies that benthic cyanobacteria may pose a higher environmental risk in China than previously acknowledged.

Distribution of toxigenic cyanobacteria in Alpine lakes and rivers as revealed by molecular screening

The increasing frequency of cyanobacteria blooms in waterbodies caused by ecosystem eutrophication could endanger human health. This risk can be mitigated by effective monitoring incorporating molecular methods. To date, most molecular studies on toxigenic cyanobacteria have been limited to microcystins (MCs), disregarding other cyanotoxins, to freshwater planktic habitats while ignoring benthic habitats, and to limited geographic areas (usually one or a few specific waterbodies). In this study, we used PCR-based methods including PCR product sequencing and chemical-analytical methods (LC-MS/MS) to screen many plankton (n = 123) and biofilm samples (n = 113) originating from 29 Alpine lakes and 18 rivers for their cyanotoxin production potential. Both mcyE (indicating MC synthesis) and anaC (indicating anatoxin (ATX) synthesis) gene fragments were able to qualitatively predict MC or ATX occurrence. The abundance of mcyE gene fragments was significantly related to MC concentrations in plankton samples (R2 = 0.61). mcyE gene fragments indicative of MC synthesis were most abundant in planktic samples (65 %) and were assigned to the genera Planktothrix and Microcystis. However, mcyE rarely occurred in biofilms of lakes and rivers, i.e., 4 % and 5 %, respectively, and were assigned to Microcystis, Planktothrix, and Nostoc. In contrast, anaC gene fragments occurred frequently in planktic samples (14 % assigned to Tychonema, Phormidium (Microcoleus), and Oscillatoria), but also in biofilms of lakes (49 %) and rivers (18 %) and were assigned to the genera Phormidium, Oscillatoria, and Nostocales. The cyrJ gene fragment indicating cylindrospermopsin synthesis occurred only once in plankton (assigned to Dolichospermum), while saxitoxin synthesis potential was not detected. For plankton samples, monomictic and less eutrophic conditions were positively related to mcyE/MC occurrence frequency, while oligomictic conditions were related to anaC/ATX frequency. The anaC/ATX frequency in biofilm was related to the lake habitats generally showing higher biodiversity as revealed from metabarcoding in a parallel study.

New records on toxic cyanobacteria from Brazil: Exploring their occurrence and geography

Cyanobacterial Harmful Algal Blooms (CyanoHABs) pose a significant threat to communities globally, impacting ecosystems and public health. This study provides an in-depth review of the current state of cyanotoxins and the distribution of CyanoHABs species in Brazil, while also detailing the methods used for their detection. Four hundred and twenty-one incidents were analyzed from 1993 to 2021, compiling cyanotoxin records and toxic CyanoHABs occurrences. The investigation begins with the first detection of microcystins in 1994 and highlights pivotal moments, like the 1996 "Caruaru Syndrome" outbreak. This event encouraged research and updated cyanotoxin-monitoring guidelines. The Brazilian drought period of 2015-2016 exacerbated cyanobacterial growth and saxitoxin levels, coinciding with Zika-related microcephaly. This study delves into methods used for cyanotoxin analysis, including ELISA, bioassays, HPLC, and LC-MS. Additionally, we investigated the toxicity of 37 cyanobacterial strains isolated from various Brazilian environments. Extracts were tested against Artemia salina and analyzed by LC-MS. Results revealed toxicity in extracts from 49 % of cyanobacterial strains. LC-MS results were analyzed using GNPS MS/MS molecular networking for comparing experimental spectra with those of cyanotoxin standards against in-house databases and the existing literature. Our research underscores the variability in cyanotoxin production among species and over time, extending beyond microcystins. LC-MS results, interpreted through the GNPS platform, revealed six cyanotoxin groups in Brazilian strains. Yet, compounds present in 75 % of the toxic extracts remained unidentified. Further research is crucial for fully comprehending the impact of potentially harmful organisms on water quality and public health management strategies. The study highlights the urgent need for continuously monitoring cyanobacteria and the cyanotoxin inclusion of management in public health policies.

Polyphasic Approach and Potential Cyanotoxin Production by Planktothrix from the Río Grande de Comitán and Montebello Lakes National Park, Southern Mexico

The development of anthropic activities during recent years has led to an increase in nutrient fluxes in the Río Grande de Comitán and Montebello Lakes National Park, Mexico. In turn, this has modified the dynamics of the biotic community, specifically favoring the presence of cyanobacteria tolerant to contamination. The continual and massive presence of Planktothrix species (spp.) in the system suggests a potential detrimental impact for economic issues and human health. In this study, we identify the morphological and molecular characteristics of Planktothrix populations from seven tropical (1,380-1,740 masl, 23.0-25.5°C) and calcareous lakes and two ponds from a water treatment plant. We also assess the ecological drivers that could be related to the presence of cyanotoxins in the system. The ecological preferences, morphology, 16S rRNA structure, and 16S-23S rRNA internal transcribed spacer found evidence for three species: P. agardhii distributed in neutral to slightly basic water (pH = 7.7-8.7), and P. spiroides and Planktothrix sp. in alkaline waters (pH = 9.1). The presence of the mcyE gene and its validation by liquid chromatography confirmed the presence of two microcystin variants (MC-RR and MC-LR) in at least three populations of P. agardhii. These microcystins put the health of the ecosystem and its inhabitants at risk, a condition that should be addressed and resolved with a water management and detoxification strategy in the basin.

Consumption of toxic benthic cyanobacteria by two common demersal fish: Growth, antioxidant and liver histopathology responses

Benthic freshwater cyanobacteria have the potential to produce toxins. Compared with more extensively studied plankton species, little is known about the impact of harmful benthic cyanobacteria on aquatic organisms. As demersal fish are usually in direct contact with benthic cyanobacteria, it is important to understand their interactive effects. This study investigated the physio-chemical responses of two demersal fish (Xenocypris davidi and Crucian carp) after exposure to benthic Oscillatoria (producing cylindrospermopsin, 2 × 106 cells/mL) for 7 days. Interestingly, benthic Oscillatoria had less adverse effects on X. davidi than C. carp. The two demersal fish effectively ingested Oscillatoria, but Oscillatoria cell sheathes could not be fully digested in C. carp intestines and led to growth inhibition. Oscillatoria consumption induced oxidative stress and triggered alterations in detoxification enzyme activities in the X. davidi liver. Superoxide dismutase (SOD) and glutathione reductase (GR) activities significantly increased in the C. carp liver, but catalase (CAT) and detoxification enzymes glutathione S-transferase (GST) and glutathione (GSH) activities were insignificantly changed. This suggested that C. carp may have a relatively weak detoxification capacity for toxic Oscillatoria. Oscillatoria ingestion led to more pronounced liver pathological changes in C. carp, including swelling, deformation, and loss of cytoskeleton structure. Simultaneously, fish consumption of Oscillatoria increased extracellular cylindrospermopsin concentration. These results provide valuable insights into the ecological risks associated with benthic cyanobacteria in aquatic ecosystems.

Cyanobacteria and Macroinvertebrate Relationships in Freshwater Benthic Communities beyond Cytotoxicity

Cyanobacteria are harmful algae that are monitored worldwide to prevent the effects of the toxins that they can produce. Most research efforts have focused on direct or indirect effects on human populations, with a view to gain easy accurate detection and quantification methods, mainly in planktic communities, but with increasing interest shown in benthos. However, cyanobacteria have played a fundamental role from the very beginning in both the development of our planet's biodiversity and the construction of new habitats. These organisms have colonized almost every possible planktic or benthic environment on earth, including the most extreme ones, and display a vast number of adaptations. All this explains why they are the most important or the only phototrophs in some habitats. The negative effects of cyanotoxins on macroinvertebrates have been demonstrated, but usually under conditions that are far from natural, and on forms of exposure, toxin concentration, or composition. The cohabitation of cyanobacteria with most invertebrate groups is long-standing and has probably contributed to the development of detoxification means, which would explain the survival of some species inside cyanobacteria colonies. This review focuses on benthic cyanobacteria, their capacity to produce several types of toxins, and their relationships with benthic macroinvertebrates beyond toxicity.

Cyanobacterial Harmful Algal Mats (CyanoHAMs) in tropical rivers of central Mexico and their potential risks through toxin production

Cyanobacteria inhabiting lotic environments have been poorly studied and characterized in Mexico, despite their potential risks from cyanotoxin production. This article aims to fill this knowledge gap by assessing the importance of benthic cyanobacteria as potential cyanotoxin producers in central Mexican rivers through: (i) the taxonomic identification of cyanobacteria found in these rivers, (ii) the environmental characterization of their habitats, and (iii) testing for the presence of toxin producing genes in the encountered taxa. Additionally, we introduce and discuss the use of the term "CyanoHAMs" for lotic water environments. Populations of cyanobacteria were collected from ten mountain rivers and identified using molecular techniques. Subsequently, these taxa were evaluated for genes producing anatoxins and microcystins via PCR. Through RDA analyses, the collected cyanobacteria were grouped into one of three categories based on their environmental preferences for the following: (1) waters with high ionic concentrations, (2) cold-temperate waters, or (3) waters with high nutrient enrichment. Populations from six locations were identified to genus level: Ancylothrix sp., Cyanoplacoma sp., and Oxynema sp. The latter was found to contain the gene that produces anatoxins and microcystins in siliceous rivers, while Oxynema tested positive for the gene that produces microcystins in calcareous rivers. Our results suggest that eutrophic environments are not necessarily required for toxin-producing cyanobacteria. Our records of Compactonostoc, Oxynema, and Ancylothrix represent the first for Mexico. Four taxa were identified to species level: Wilmottia aff. murrayi, Nostoc tlalocii, Nostoc montejanii, and Dichothrix aff. willei, with only the first testing positive using PCR for anatoxin and microcystin-producing genes in siliceous rivers. Due to the differences between benthic growths with respect to planktonic ones, we propose the adoption of the term Cyanobacterial Harmful Algal Mats (CyanoHAMs) as a more precise descriptor for future studies.

Divide and conquer: Spatial and temporal resource partitioning structures benthic cyanobacterial mats

Benthic cyanobacterial mats are increasing in abundance worldwide with the potential to degrade ecosystem structure and function. Understanding mat community dynamics is thus critical for predicting mat growth and proliferation and for mitigating any associated negative effects. Carbon, nitrogen, and sulfur cycling are the predominant forms of nutrient cycling discussed within the literature, while metabolic cooperation and viral interactions are understudied. Although many forms of nutrient cycling in mats have been assessed, the links between niche dynamics, microbial interactions, and nutrient cycling are not well described. Here, we present an updated review on how nutrient cycling and microbial community interactions in mats are structured by resource partitioning via spatial and temporal heterogeneity and succession. We assess community interactions and nutrient cycling at both intramat and metacommunity scales. Additionally, we present ideas and recommendations for research in this area, highlighting top-down control, boundary layers, and metabolic cooperation as important future directions.

Proliferation and anatoxin production of benthic cyanobacteria associated with canine mortalities along a stream-lake continuum

Proliferations of benthic cyanobacteria are increasingly in the public eye, with rising animal deaths associated with benthic rather than planktonic blooms. In early June 2021, two dogs died after consuming material on the shore of Shubenacadie Grand Lake, Nova Scotia. Preliminary investigations indicated anatoxins produced by benthic cyanobacterial mats were responsible for the deaths. In this study, we monitored the growth of a toxic benthic cyanobacterial species (Microcoleus sp.) along a stream-lake continuum where the canine poisonings occurred. We found that the species was able to proliferate in both lentic and lotic environments, but temporal growth dynamics and the predominant sub-species were influenced by habitat type, and differed with hydrodynamic setting, nutrient and sunlight availability. Toxin concentration was greatest in cyanobacterial mats growing in the oligotrophic lakeshore environment (maximum measured total anatoxins (ATXs) >20 mg·kg-1 wet weight). This corresponded with a shift in the profile of ATX analogues, which also indicated changing sub-species dominance along the stream-lake transition.

Physico-chemical treatments for the removal of cyanotoxins from drinking water: Current challenges and future trends

Cyanobacteria are highly prevalent blue-green algae that grow in stagnant and nutrient-rich water bodies. Environmental conditions, such as eutrophication and human activities, increased the cyanobacterial blooms in freshwater resources worldwide. The excessive bloom formation has also resulted in an alarming surge of cyanobacterial toxins. Prolonged exposure to cyanotoxins is a potential threat to natural ecosystems, animal and human health by the spoilage of the quality of bathing and drinking water. Various molecular and analytical methods have been proposed to monitor their occurrence and understand their global distribution. Moreover, different physical, chemical, and biological approaches have been employed to control cyanobacterial blooms and their toxins to mitigate their occurrence. Numerous strategies have been engaged in drinking water treatment plants (DWTPs). However, the degree of treatment varies greatly and is primarily determined by the source, water properties, and operating parameters such as temperature, pH, and cyanotoxin variants and levels. A comprehensive compilation of methods, from traditional approaches to more advanced oxidation processes (AOPs), are presented for the removal of intracellular and extracellular cyanotoxins. This review discusses the effectiveness of various physicochemical operations and their limitations in a DWTP, for the removal of various cyanotoxins. These operations span from simple to advanced treatment levels with varying degrees of effectiveness and differing costs of implementation. Furthermore, mitigation measures applied in other toxin systems have been considered as alternative strategies.

The toxicological effects of life-cycle exposure to harmful benthic cyanobacteria Oscillatoria on zebrafish growth and reproduction: A comparative study with planktonic Microcystis

The risks of planktonic cyanobacteria blooms have been the focus of much scientific research, but studies on the ecotoxicological effects of benthic cyanobacteria are lagging. The impacts of cyanobacteria cells on fish populations might be more complex in contrast to purified cyanotoxins or cyanobacteria extracts. This study systematically compared the chronic effects of benthic Oscillatoria sp. (producing cylindrospermopsins) and planktonic Microcystis aeruginosa (producing microcystins) on the growth and reproduction of zebrafish through life-cycle exposure (5- 90 days post fertilization). The results showed that both Oscillatoria sp. and M. aeruginosa exposure caused growth inhibition and fecundity reduction in F0 generation by disrupting sex hormone levels, delayed ovarian and sperm development, and induced pathological lesions in zebrafish gonads. Furthermore, exposure to Oscillatoria sp. or M. aeruginosa in adult zebrafish increased mortality and teratogenicity in F1 embryos (without exposure), indicating a parental transmission effect of developmental toxicity. The difference was that M. aeruginosa exposure led to significant alterations in pathways, such as tissue development, redox processes, and steroid hormone synthesis. In contrast, Oscillatoria sp. exposure primarily disrupted the PPAR signaling pathway, cell adhesion molecules, and lipid transport pathways. Interestingly, the differentially expressed genes revealed that male fish were more sensitive to harmful cyanobacteria than females, whether exposed to Oscillatoria sp. or M. aeruginosa. These findings contribute to a better mechanistic understanding of the chronic toxic effects of distinct types of harmful cyanobacteria, suggesting that the ecological risk of benthic cyanobacteria requires further attention.

Environmental Factors Impacting the Development of Toxic Cyanobacterial Proliferations in a Central Texas Reservoir

Cyanobacterial harmful algal proliferations (cyanoHAPs) are increasingly associated with dog and livestock deaths when benthic mats break free of their substrate and float to the surface. Fatalities have been linked to neurotoxicosis from anatoxins, potent alkaloids produced by certain genera of filamentous cyanobacteria. After numerous reports of dog illnesses and deaths at a popular recreation site on Lady Bird Lake, Austin, Texas in late summer 2019, water and floating mat samples were collected from several sites along the reservoir. Water quality parameters were measured and mat samples were maintained for algal isolation and DNA identification. Samples were also analyzed for cyanobacterial toxins using LC-MS. Dihydroanatoxin-a was detected in mat materials from two of the four sites (0.6-133 ng/g wet weight) while water samples remained toxin-free over the course of the sampling period; no other cyanobacterial toxins were detected. DNA sequencing analysis of cyanobacterial isolates yielded a total of 11 genera, including Geitlerinema, Tyconema, Pseudanabaena, and Phormidium/Microcoleus, taxa known to produce anatoxins, including dihydroanatoxin, among other cyanotoxins. Analyses indicate that low daily upriver dam discharge, higher TP and NO3 concentrations, and day of the year were the main parameters associated with the presence of toxic floating cyanobacterial mats.

Novel virulent and temperate cyanophages predicted to infect Microcoleus associated with anatoxin-producing benthic mats

Cyanophages are crucial for regulating cyanobacterial populations, but their influence on anatoxin-producing Microcoleus mat dynamics remains unexplored. Here, we use metagenomics to explore phage presence in benthic mats from the Wolastoq|Saint John River (New Brunswick, Canada) and the Eel River (California, USA). We recovered multiple viral-like sequences associated with different putative bacterial hosts, including two cyanophage genomes with apparently different replication strategies. A temperate cyanophage was found integrated in the genomes of Microcoleus sp. 3 recovered from the Eel River and is phylogenetically related to Phormidium phages. We also recovered novel virulent cyanophage genomes from Wolastoq and Eel River mats that were dominated by anatoxin-producing Microcoleus species predicted to be the host. Despite the geographical distance, these genomes have similar sizes (circa 239 kbp) and share numerous orthologous genes with high sequence identity. A considerable reduction of the anatoxin-producing Microcoleus species in Wolastoq mats following the emergence of the virulent phage suggests that phage infections have an important role in limiting the abundance of this toxigenic cyanobacterium and releasing anatoxins into the surrounding water. Our results constitute the first report of cyanophages predicted to infect mat-forming Microcoleus species associated with anatoxin production.

Quantitative relationships among high-throughput sequencing, cyanobacteria toxigenic genotype abundance and microcystin occurrence in bathing waters

Toxin-producing cyanobacteria pose significant threats to human and animal health if exposed during recreational activities in bathing waters. To better safeguard public health and reduce health risks during the bathing season, an effective monitoring and management strategy is required. Molecular tools used to monitor toxigenic cyanobacteria have been evaluated on the basis of the efficiency and applicability of the method used to (i) establish an early-warning monitoring strategy for EU bathing water sites using both targeted quantitative polymerase chain reaction (qPCR) and non-targeted high-throughput sequencing (HTS) genotype analysis and (ii) to compare the toxigenic potential of cyanobacteria with actual microcystin (MC) occurrence and concentrations. For this purpose, 16 bathing water sites were monitored according to the bathing water directive (BWD) of the European Union (EU) during the bathing season of the summer of 2020 in eastern Austria. The cyanobacterial community composition was analyzed through HTS and qPCR by targeting the microcystin synthetase B gene (mcyB), which indicates MC synthesis within the genera Microcystis and Planktothrix. Within the genus Microcystis, which was identified as the primary MC producer, the mcyB genotypes formed stable subpopulations that increased linearly in correlation with the total Microcystis population. Notably, the HTS cell equivalents assigned to Microcystis and Planktothrix correlated with the corresponding qPCR estimates of genotype abundance, which serves as a confirmation of the suitability of (semi)-quantitative sequencing through HTS. In addition to the elevated trophic state, reduced transparency, increasing water temperatures, as well as cyanobacterial HTS read numbers and Microcystis cell number equivalents per mL estimated through qPCR, were associated with positive MC samples. Therefore, in combination with the monitoring of standard environmental parameters, the use of HTS and qPCR techniques is considered highly useful to ensure the timely identification of health risks to recreational users, as mandated by the BWD.

An exploration of the binding prediction of anatoxin-a and atropine to acetylcholinesterase enzyme using multi-level computer simulations

Acetylcholinesterase (AChE) is crucial for the breakdown of acetylcholine to acetate and choline, while the inhibition of AChE by anatoxin-a (ATX-a) results in severe health complications. This study explores the structural characteristics of ATX-a and its interactions with AChE, comparing to the reference molecule atropine for binding mechanisms. Molecular docking simulations reveal strong binding affinity of both ATX-a and atropine to AChE, interacting effectively with specific amino acids in the binding site as potential inhibitors. Quantitative assessment using the MM-PBSA method demonstrates a significantly negative binding free energy of -81.659 kJ mol-1for ATX-a, indicating robust binding, while atropine exhibits a stronger binding affinity with a free energy of -127.565 kJ mol-1. Umbrella sampling calculates the ΔGbindvalues to evaluate binding free energies, showing a favorable ΔGbindof -36.432 kJ mol-1for ATX-a and a slightly lower value of -30.12 kJ mol-1for atropine. This study reveals the dual functionality of ATX-a, acting as both a nicotinic acetylcholine receptor agonist and an AChE inhibitor. Remarkably, stable complexes form between ATX-a and atropine with AChE at its active site, exhibiting remarkable binding free energies. These findings provide valuable insights into the potential use of ATX-a and atropine as promising candidates for modulating AChE activity.

Biofilm community composition is changing in remote mountain lakes with a relative increase in potentially toxigenic algae

Mountain lakes provide clear drinking water to humankind but are strongly impacted by global change. Benthic biofilms are crucial for maintaining water quality in these oligotrophic lakes, yet little is known about the effects of global change on mountain biofilm communities. By combining analyses of metabarcoding data on 16S and 18S rRNA genes with climatic and environmental data, we investigated global change effects on the composition of biofilm prokaryotic and micro-eukaryotic assemblages in a five-year monitoring program of 26 Pyrenean lakes (2016-2020). Using time-decay relationships and within-lake dissimilarity modelling, we show that the composition of both prokaryotic and micro-eukaryotic biofilm communities significantly shifted and their biodiversity declined from 2016 to 2020. In particular, analyses of temporal trends with linear mixed models indicated an increase in the richness and relative abundance of cyanobacteria, including potentially toxigenic cyanobacteria, and a concomitant decrease in diatom richness and relative abundance. While these compositional shifts may be due to several drivers of global change acting simultaneously on mountain lake biota, water pH and hardness were, from our data, the main environmental variables associated with changes for both prokaryotic and micro-eukaryotic assemblages. Water pH and hardness increased in our lakes over the study period, and are known to increase in Pyrenean lakes due to the intensification of rock weathering as a result of climate change. Given predicted climate trends and if water pH and hardness do cause some changes in benthic biofilms, those changes might be further exacerbated in the future. Such biofilm compositional shifts may induce cascading effects in mountain food webs, threatening the resilience of the entire lake ecosystem. The rise in potentially toxigenic cyanobacteria also increases intoxication risks for humans, pets, wild animals, and livestock that use mountain lakes. Therefore, our study has implications for water quality, ecosystem health, public health, as well as local economies (pastoralism, tourism), and highlights the possible impacts of global change on mountain lakes.

More than just an eagle killer: The freshwater cyanobacterium Aetokthonos hydrillicola produces highly toxic dolastatin derivatives

Cyanobacteria are infamous producers of toxins. While the toxic potential of planktonic cyanobacterial blooms is well documented, the ecosystem level effects of toxigenic benthic and epiphytic cyanobacteria are an understudied threat. The freshwater epiphytic cyanobacterium Aetokthonos hydrillicola has recently been shown to produce the "eagle killer" neurotoxin aetokthonotoxin (AETX) causing the fatal neurological disease vacuolar myelinopathy. The disease affects a wide array of wildlife in the southeastern United States, most notably waterfowl and birds of prey, including the bald eagle. In an assay for cytotoxicity, we found the crude extract of the cyanobacterium to be much more potent than pure AETX, prompting further investigation. Here, we describe the isolation and structure elucidation of the aetokthonostatins (AESTs), linear peptides belonging to the dolastatin compound family, featuring a unique modification of the C-terminal phenylalanine-derived moiety. Using immunofluorescence microscopy and molecular modeling, we confirmed that AEST potently impacts microtubule dynamics and can bind to tubulin in a similar matter as dolastatin 10. We also show that AEST inhibits reproduction of the nematode Caenorhabditis elegans. Bioinformatic analysis revealed the AEST biosynthetic gene cluster encoding a nonribosomal peptide synthetase/polyketide synthase accompanied by a unique tailoring machinery. The biosynthetic activity of a specific N-terminal methyltransferase was confirmed by in vitro biochemical studies, establishing a mechanistic link between the gene cluster and its product.

Understanding the Risks of Diffusion of Cyanobacteria Toxins in Rivers, Lakes, and Potable Water

Blue-green algae, or cyanobacteria, may be prevalent in our rivers and tap water. These minuscule bacteria can grow swiftly and form blooms in warm, nutrient-rich water. Toxins produced by cyanobacteria can pollute rivers and streams and harm the liver and nervous system in humans. This review highlights the properties of 25 toxin types produced by 12 different cyanobacteria genera. The review also covered strategies for reducing and controlling cyanobacteria issues. These include using physical or chemical treatments, cutting back on fertilizer input, algal lawn scrubbers, and antagonistic microorganisms for biocontrol. Micro-, nano- and ultrafiltration techniques could be used for the removal of internal and extracellular cyanotoxins, in addition to powdered or granular activated carbon, ozonation, sedimentation, ultraviolet radiation, potassium permanganate, free chlorine, and pre-treatment oxidation techniques. The efficiency of treatment techniques for removing intracellular and extracellular cyanotoxins is also demonstrated. These approaches aim to lessen the risks of cyanobacterial blooms and associated toxins. Effective management of cyanobacteria in water systems depends on early detection and quick action. Cyanobacteria cells and their toxins can be detected using microscopy, molecular methods, chromatography, and spectroscopy. Understanding the causes of blooms and the many ways for their detection and elimination will help the management of this crucial environmental issue.

Occurrence, Distribution and Toxins of Benthic Cyanobacteria in German Lakes

Cyanobacteria are favored by climate change and global warming; however, to date, most research and monitoring programs have focused on planktic cyanobacteria. Benthic cyanobacteria blooms also increase and pose a risk to animal and human health; however, there is limited knowledge of their occurrence, distribution and the toxins involved, especially in relation to their planktic conspecifics. Therefore, we analyzed the benthic and planktic life forms of cyanobacterial communities in 34 lakes in Germany, including a monitoring of cyanotoxins. Community analyses were based on microscopic examination and Illumina sequencing of the 16S rRNA gene. The analyses of cyanotoxins were carried out using LC-MS/MS and ELISA. Observed benthic mats containing cyanobacteria consisted mainly of Nostocales and Oscillatoriales, being present in 35% of the lakes. Anatoxin was the most abundant cyanotoxin in the benthic samples, reaching maximum concentrations of 45,000 µg/L, whereas microcystin was the predominate cyanotoxin in the open-water samples, reaching concentrations of up to 18,000 µg/L. Based on the results, specific lakes at risk of toxic cyanobacteria could be identified. Our findings suggest that monitoring of benthic cyanobacteria and their toxins should receive greater attention, ideally complementing existing open-water sampling programs with little additional effort.

Limnofasciculus baicalensis gen. et sp. nov. (Coleofasciculaceae, Coleofasciculales): A New Genus of Cyanobacteria Isolated from Sponge Fouling in Lake Baikal, Russia

The proliferation of benthic cyanobacteria has been observed in Lake Baikal since 2011 and is a vivid manifestation of the ecological crisis occurring in the littoral zone. The cyanobacterium Symplocastrum sp. has formed massive fouling on all types of benthic substrates, including endemic Baikal sponges. The strain BBK-W-15 (=IPPAS B-2062^T), which was isolated from sponge fouling in 2015, was used for further taxonomic determination. A polyphasic approach revealed that it is a cryptic taxon of cyanobacteria. Morphological evaluation of the strain indicated the presence of cylindrical filaments with isodiametric cells enclosed in individual sheaths and coleodesmoid false branching. Strain ultrastructure (fascicular thylakoids and type C cell division) is characteristic of the Microcoleaceae and Coleofasciculaceae families. An integrated analysis that included 16S rRNA gene phylogeny, conserved protein phylogeny and whole-genome comparisons indicated the unique position of BBK-W-15, thus supporting the proposed delineation of the new genus Limnofasciculus. Through characterisation by morphology, 16S, ITS and genomic analysis, a new cyanobacterium of the family Coleofasciculaceae Limnofasciculus baicalensis gen. et sp. nov. was described.

Occurrence of aetokthonotoxin producer in natural samples - A PCR protocol for easy detection

Cyanobacteria are well known producers of bioactive metabolites, including harmful substances. The recently discovered "eagle killer" neurotoxin aetokthonotoxin (AETX) is produced by the epiphytic cyanobacterium Aetokthonos hydrillicola growing on invasive water thyme (Hydrilla verticillata). The biosynthetic gene cluster of AETX was previously identified from an Aetokthonos strain isolated from the J. Strom Thurmond Reservoir, Georgia, USA. Here, a PCR protocol for easy detection of AETX-producers in environmental samples of plant-cyanobacterium consortia was designed and tested. Three different loci of the AETX gene cluster were amplified to confirm the genetic potential for AETX production, along with two variable types of rRNA ITS regions to confirm the homogeneity of the producer´s taxonomic identity. In samples of Hydrilla from three Aetokthonos-positive reservoirs and one Aetokthonos-negative lake, the PCR of all four loci provided results congruent with the Aetokthonos presence/absence detected by light and fluorescence microscopy. The production of AETX in the Aetokthonos-positive samples was confirmed using LC-MS. Intriguingly, in J. Strom Thurmond Reservoir, recently Hydrilla free, an Aetokthonos-like cyanobacterium was found growing on American water-willow (Justicia americana). Those specimens were positive for all three aet markers but contained only minute amounts of AETX. The obtained genetic information (ITS rRNA sequence) and morphology of the novel Aetokthonos distinguished it from all the Hydrilla-hosted A. hydrillicola, likely at the species level. Our results suggest that the toxigenic Aetokthonos spp. can colonize a broader array of aquatic plants, however the level of accumulation of the toxin may be driven by host-specific interactions such as the locally hyper-accumulated bromide in Hydrilla.

Harmful algae blooms: an analysis of recent spatiotemporal trends on California's inland waterbodies

Harmful algae blooms (HABs) are unwelcome annual events on waterbodies in California (USA). The unseemly sights of lifeless fish drifting ashore and the mammalian illnesses resulting from close contacts with HABs once in ahile are telltale signs of their presence. California as such tracks HABs closely for immediate public warnings. That said, a lack of statewide monitoring standards for producing comparable and high-quality data, however, hinders a deeper insight into HABs on California's inland waterbodies. In their absence, the current study demonstrates the utility of empirical dataset in advancing an understanding of spatiotemporal distribution of HABs on inland waterbodies. With a 2016-2021 mostly observational data, the questions asked are whether HABs incidences are expanding in California with time, whether there are localities more prone to HABs than others, and whether bivariate relationships exist between HABs reports and population density, or waterbody size, land area and geographical location. Overall, the frequency with which HABs are observed is found to increase statewide, an increase not correlated with population density, but with land area and inland waterbody size. Results also show that North Coast, Central Valley, and San Diego are the most affected regions of California. Also revealed by this mostly observational data were recent HABs spikes in the January months (California winter) which, if proven, may be signaling an emerging year-round problem that California will have to contend with.

Relative effect of hydraulics, physico-chemistry and other biofilm algae on benthic cyanobacteria assemblages in a regulated river

The development of benthic cyanobacteria currently raises concern worldwide because of their potential to produce toxins. As a result, understanding which measures of biotic and abiotic parameters influence the development of cyanobacterial assemblages is of great importance to guide management actions. In this study, we investigate the relative contributions of abiotic and biotic parameters that may drive the development of cyanobacterial assemblages in river biofilms. First, a 2D hydrodynamic model allowed us to retrace changes in depths and velocities according to discharge at a 4 m² resolution. From this model, we set up three hydraulic zones in each of the 4 reaches investigated along a 50-km-long river stretch. We further used univariate, multivariate and variance partitioning analyses to assess the contribution of past and present hydraulics, present physical and chemical parameters and algae to the temporal variability of cyanobacterial assemblage composition. The cyanobacterial assemblages were generally dominated by Phormidium sp., Lyngbya sp., Planktolyngbya sp. and Oscillatoria sp., four genera known to contain potentially toxic species. The highest biovolumes of cyanobacteria were present in low velocity zones in early summer and shifted to high velocity zones in late summer, highlighting the major influence of hydraulic parameters on benthic cyanobacteria settlement and development in rivers. Considering the identified genera, biofilms present a potentially high risk of toxin production. Relations between cyanobacterial development, toxin production and environmental parameters need to be further assessed to better estimate this risk.

Genomic characterization of coexisting anatoxin-producing and non-toxigenic Microcoleus subspecies in benthic mats from the Wolastoq, New Brunswick, Canada

The presence of toxigenic benthic cyanobacteria in riverine ecosystems is an increasing concern around the world. In 2018, the death of three dogs along the Wolastoq (also known as the Saint John River) in New Brunswick, Canada, was attributed to anatoxin exposure after they ingested benthic microbial mats found along the shore. Here, we shotgun sequenced the DNA of 15 non-axenic cyanobacterial isolates derived from four anatoxin-containing benthic mat samples associated with the dog deaths. Anatoxins were produced by some of the isolates, but not all. We retrieved near-complete Microcoleus metagenome-assembled genomes (MAGs) from the isolates that are closely related to anatoxin-producing Microcoleus from the Cardrona River (New Zealand), although the Microcoleus MAGs from the Wolastoq varied in the presence/absence of the anatoxin-a biosynthesis cluster. Sequence similarity at the genomic level suggests that toxigenic and non-toxigenic Microcoleus MAGs from the Wolastoq belong to the same species but are separate subspecies. The toxigenic and nontoxic Wolastoq Microcoleus subspecies coexisted in the mat samples in similar relative abundance. Overall genomic comparisons revealed that toxigenic Microcoleus MAGs are longer and code for more accessory genes than their non-toxigenic relatives, suggesting a differential responsiveness to changing environments, stress conditions and nutrient availability.

Integrative monitoring strategy for marine and freshwater harmful algal blooms and toxins across the freshwater-to-marine continuum

Many coastal states throughout the USA have observed negative effects in marine and estuarine environments caused by cyanotoxins produced in inland waterbodies that were transported downstream or produced in the estuaries. Estuaries and other downstream receiving waters now face the dual risk of impacts from harmful algal blooms (HABs) that occur in the coastal ocean as well as those originating in inland watersheds. Despite this risk, most HAB monitoring efforts do not account for hydrological connections in their monitoring strategies and designs. Monitoring efforts in California have revealed the persistent detection of cyanotoxins across the freshwater-to-marine continuum. These studies underscore the importance of inland waters as conduits for the transfer of cyanotoxins to the marine environment and highlight the importance of approaches that can monitor across hydrologically connected waterbodies. A HAB monitoring strategy is presented for the freshwater-to-marine continuum to inform HAB management and mitigation efforts and address the physical and hydrologic challenges encountered when monitoring in these systems. Three main recommendations are presented based on published studies, new datasets, and existing monitoring programs. First, HAB monitoring would benefit from coordinated and cohesive efforts across hydrologically interconnected waterbodies and across organizational and political boundaries and jurisdictions. Second, a combination of sampling modalities would provide the most effective monitoring for HAB toxin dynamics and transport across hydrologically connected waterbodies, from headwater sources to downstream receiving waterbodies. Third, routine monitoring is needed for toxin mixtures at the land-sea interface including algal toxins of marine origins as well as cyanotoxins that are sourced from inland freshwater or produced in estuaries. Case studies from California are presented to illustrate the implementation of these recommendations, but these recommendations can also be applied to inland states or regions where the downstream receiving waterbody is a freshwater lake, reservoir, or river. Integr Environ Assess Manag 2023;19:586-604. © 2022 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Anatoxins from benthic cyanobacteria responsible for dog mortalities in New Brunswick, Canada

In July 2018 three dogs died after visiting the Wolastoq (Saint John River) near Fredericton, New Brunswick, in Atlantic Canada. All showed signs of toxicosis, and necropsies revealed non-specific pulmonary edema and multiple microscopic brain hemorrhages. Liquid chromatography-high-resolution mass spectrometry (LC-HRMS) analysis of vomitus and stomach contents as well as water and biota from the mortality sites confirmed the presence of anatoxins (ATXs), a class of potent neurotoxic alkaloids. The highest levels were measured in a dried benthic cyanobacterial mat that two of the dogs had been eating before falling ill and in a vomitus sample collected from one of the dogs. Concentrations of 357 and 785 mg/kg for anatoxin-a and dihydroanatoxin-a, respectively, were measured in the vomitus. Known anatoxin-producing species of Microcoleus were tentatively identified using microscopy and confirmed by 16S rRNA gene sequencing. The ATX synthetase gene, anaC, was detected in the samples and isolates. The pathology and experimental results confirmed the role of ATXs in these dog mortalities. Further research is required to understand drivers for toxic cyanobacteria in the Wolastoq and to develop methodology for assessing occurrence.

Water Quality, Toxicity and Diversity of Planktonic and Benthic Cyanobacteria in Pristine Ancient Lake Khubsugul (Hövsgöl), Mongolia

For the first time, microcystin-producing cyanobacteria have been detected in Khubsugul, which is ancient, pristine and one of the world’s largest lakes. The microcystin synthetase genes belonged to the genera Nostoc, Microcystis and possibly Snowella spp. No microcystins were found in the water of the lake. Using the HPLC-HRMS/TOF, five microcystin congeners were identified in biofilms from stony substrates sampled in the coastal zone. The concentration of microcystins in biofilms was low: 41.95 µg g−1 d. wt. by ELISA and 55.8 µg g−1 d. wt. using HPLC. The taxonomic composition of planktonic and benthic cyanobacterial communities was determined by means of microscopy and high-throughput sequencing of 16S rDNA amplicons. Nostocales cyanobacteria dominated benthos of Lake Khubsugul and Synechococcales—plankton. The abundance of cyanobacteria was low both in plankton and benthos; there was no mass development of cyanobacteria. Hydrochemical and microbiological analyses showed that the water in the lake was clean; the number of faecal microorganisms was significantly below the acceptable guideline values. Hydrochemical and hydrophysical parameters, and the concentration of chlorophyll a, were low and within the range of values recorded in the 1970s to 1990s, and corresponded to the oligotrophic state of the lake. There were no signs of anthropogenic eutrophication of the lake and no conditions for the cyanobacterial blooms.

Gloeotrichia pisum in Lake Kinneret: A successful epiphytic cyanobacterium

With climate change and re-oligotrophication of lakes due to restoration efforts, the relative importance of benthic cyanobacteria is increasing, but they are much less studied than their planktonic counterparts. Following a major water level rise event that inundated massive reed stands in Lake Kinneret, Israel, we discovered the appearance of a vast abundance of Gloeotrichia pisum (cyanobacteria). This provided an opportunity to investigate the biology and ecology of a benthic epiphytic colonial cyanobacterium, proliferating under altered environmental conditions, with possible toxin production potential and as a model for an invasive epiphyte. The species was identified by its typical morphology, and by sequencing its 16S rRNA gene and the intragenic space. We report on the abundance and spatial distribution of the detected colonies, their morphological characteristics, and pigment composition. High phycoerythrin content provides a brownish color and supports growth at low light levels. Genomic community composition analysis revealed that G. pisum colonies host a diverse microbial community of microalgae, cyanobacteria, bacteria, and archaea with a conserved and characteristic taxonomic composition. The Synechococcales order showed high relative abundance in the colony, as well as other prokaryotes producing secondary metabolites, such as the rhodopsin producer Pseudorhodobacter. The microbial consortium in the colonies performed nitrogen fixation. The diazotroph's phylogenetic relations were demonstrated. Tests for the presence of cyanotoxins (microcystin and cylindrospermopsin) proved negative. This study is the first documentation of this genus in Israel, providing insights into the invasive nature of G. pisum and the ecological implications of its appearance in a lake ecosystem.

Response of cyanobacterial mats to ambient phosphate fluctuations: phosphorus cycling, polyphosphate accumulation and stoichiometric flexibility

Cyanobacterial mats inhabit a variety of aquatic habitats, including the most extreme environments on Earth. They can thrive in a wide range of phosphorus (P) levels and are thus important players for ecosystem primary production and P cycling at the sediment-water interface. Polyphosphate (polyP), the major microbial P storage molecule, is assigned a critical role in compensating for phosphate fluctuations in planktonic cyanobacteria, but little is known about potentially analogous mechanisms of mat-forming cyanobacteria. To investigate acclimation strategies of cyanobacterial mats to fluctuating phosphate concentrations, laboratory batch experiments were conducted, in which the cosmopolitan mat-forming, marine cyanobacterium Sodalinema stali was exposed to low dissolved P concentrations, followed by a P pulse. Our results show that the cyanobacteria dynamically adjusted cellular P content to ambient phosphate concentrations and that they had accumulated polyP during periods of high phosphate availability, which was subsequently recycled to sustain growth during phosphate scarcity. However, following the depletion of dispensable cellular P sources, including polyP, we observed a reallocation of P contained in DNA into polyP, accompanied by increasing alkaline phosphatase activity. This suggests a change of the metabolic focus from growth towards maintenance and the attempt to acquire organic P, which would be naturally contained in the sediment. P overplus uptake following a simulated P pulse further suggests that Sodalinema-dominated mats exhibit elaborated mechanisms to cope with severe P fluctuations to overcome unfavourable environmental conditions, and potentially modulate critical P fluxes in the aquatic cycle.

Temporal variation of 2-MIB and geosmin production by Pseudanabaena galeata and Phormidium ambiguum exposed to high-intensity light

This study demonstrated the temporal variation of 2-methylisoborneol (2-MIB) and geosmin (GSM) production of two filamentous cyanobacteria species Pseudanabaena galeata (NIES-512; planktonic) and Phormidium ambiguum (NIES-2119; benthic) exposed to high light intensity (950-1000 μmol m-2  s-1 photosynthetically active radiation). The production of 2-MIB and GSM was quantified together with oxidative stress, chlorophyll content, and cellular protein content. The relative chlorophyll bleaching and cell degradations were compared through microscopic images. The 2-MIB production of P. galeata increased by over 42 ± 17% on the second day of exposure and remained leveled through the exposure period. P. ambiguum showed a continuous increase of 2-MIB until the 10th day, recording a 95 ± 4% increment. The GSM production was elevated until the fourth day of exposure by 46 ± 10% for P. galeata and by 74 ± 21% on the second day for P. ambiguum and reduced with prolonged exposure for both species. The chlorophyll content of P. galeata was reduced by 62 ± 7% on the second day, and that of P. ambiguum was reduced by 52 ± 9% on the fourth day and remained low. Protein and H2 O2 contents of both species were changed inconsistently. Exposure to high-intensity light can photobleach and deteriorate cells of both species, but elevations in odorous compounds can be expected.

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

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

Microcystin production by oscillatorialean cyanobacteria isolated from cryopreserved Antarctic mats

Twenty cyanobacterial strains of eight morphospecies isolated from deep-frozen (-15 °C) mat samples originally collected on Ross Island, in Victoria Land, and on the McMurdo Ice Shelf were screened for the presence of genes encoding for production of anatoxins, cylindrospermopsin, microcystin/nodularin and saxitoxin. One strain of each of Microcoleus autumnalis and Phormidesmis priestleyi and two strains of Wilmottia murrayi were found to produce microcystin. No toxin production was detected in the other 16 strains representing five species. The four toxin-producing strains were characterised using both morphological and molecular approaches. Phylogenetic analyses using partial 16S rRNA sequences were consistent with the morphological identification of all four strains. They were all found to contain a fragment of the mcyE gene, which is involved in microcystin biosynthesis. ELISA analysis of extracts from cultures of these strains confirmed the presence of low concentrations of microcystin: 0.35 μg/L in M. autumnalis, <0.15 μg/L in P. priestleyi, 1.60 μg/L in W. murrayi strain 1 and 0.9 μg/L in W. murrayi strain 2. This study includes the first report of microcystin synthesis by W. murrayi.

Rapid Quantitation of Anatoxins in Benthic Cyanobacterial Mats Using Direct Analysis in Real-Time-High-Resolution Tandem Mass Spectrometry

Toxic benthic cyanobacterial mats are increasingly reported worldwide as being responsible for animal mortalities due to their production of the potent neurotoxin anatoxin-a (ATX) and its analogues. Improved analytical methods for anatoxins are needed to address public health and watershed management challenges arising from extremely high spatial and temporal variability within impacted systems. We present the development, validation, and application of a direct analysis in real-time-high-resolution tandem mass spectrometry (DART-HRMS/MS) method for analysis of anatoxins in cyanobacterial field samples, including a simplified sample preparation approach. The method showed excellent sensitivity and selectivity for ATX, homoanatoxin-a, and dihydroanatoxin-a. Isotopically labeled ATX was used as an internal standard for all three analogues and successfully corrected for the matrix effects observed (86 ± 16% suppression). The limit of detection and recovery for ATX was estimated as 5 ng/g and 88%, respectively, using spiked samples. The total analysis time was ∼2 min, and excellent agreement was observed with results from a liquid chromatography-HRMS reference method. Finally, the DART-HRMS/MS method was applied to a set of 45 Microcoleus-dominated benthic cyanobacterial mat samples from the Wolastoq near Fredericton, Canada, demonstrating its power and applicability in enabling broad-scale field studies of ATX distribution.

Harmonizing science and management options to reduce risks of cyanobacteria

Management of cyanobacteria has become an increasingly complex venture. Cyanobacteria risks have amplified as society moves forward in an era of accelerated global changes. The cyanobacteria management "pendulum" has progressively shifted from prevention to mitigation, with management considerations often put forth after bloom formation. A universal system (i.e., one-size-fits-all management) fails to provide a management path forward due to the inherent complexities of each lake. A tailored management plan is needed: the right species at the right time in the right place (i.e., the three Rs). The three Rs represent a customizable management strategy that is flexible and informed by advances in scientific understanding to lower cyanobacteria-associated risks. Identifying thresholds in risk tolerance, where thresholds are defined by community collectives, is essential to frame cyanobacteria management targets and to decide on what management interventions are warranted.

Natural and anthropogenic influences on benthic cyanobacteria in streams of the northeastern United States

Benthic cyanobacteria are widespread in streams and rivers and have the potential to release toxins. In large numbers, these microorganisms and their toxins present a risk to human health. Cyanobacterial abundance in stream biofilms is typically related to single or a limited set of environmental factors, mainly light availability, water temperature, and nutrient concentrations. However, these factors may act synergistically with watershed characteristics and other stressors, such as anthropogenic pollutants, to affect cyanobacteria. We investigated the influence of multiple regional and local variables on the abundance of benthic cyanobacterial genera in streams using all subsets generalized additive modeling. We examined watershed factors (topography, geology, and climate) alongside in-stream factors (geomorphology, hydrology, pH, specific conductance, nutrients, organic contaminants, and dissolved metals) from 76 sites along an urban gradient in the northeast United States. Each genus responded to a distinct combination of environmental variables, demonstrating strong intergeneric variation in environmental selection of realized niches. Four of the 7 potentially toxigenic genera that we modeled were positively influenced by water temperature or nutrients. Nonetheless, watershed characteristics, streamflow, and/or other water quality pollutants were equally or more influential for the potentially toxigenic genera. Additionally, the relationships between cyanobacterial abundance and environmental factors varied in shape and direction across many genera. In particular, with increasing concentrations of herbicides, polychlorinated biphenyls, or metals, the abundance of roughly half of the affected genera decreased, while the others increased. These results likely demonstrate novel toxic effects of the pollutants on cyanobacterial genera in the environment, while indicating that unmeasured biotic interactions may lead to positive responses for other genera. Our results emphasize the need to consider variables beyond those that are most frequently measured or implicated (e.g., water temperature and nutrients) to more fully understand the environmental conditions that influence the distributions and abundance of potentially harmful cyanobacteria.

A whole-ecosystem experiment reveals flow-induced shifts in a stream community

The growing threat of abrupt and irreversible changes to the functioning of freshwater ecosystems compels robust measures of tipping point thresholds. To determine benthic cyanobacteria regime shifts in a potable water supply system in the tropical Andes, we conducted a whole ecosystem-scale experiment in which we systematically diverted 20 to 90% of streamflow and measured ecological responses. Benthic cyanobacteria greatly increased with a 60% flow reduction and this tipping point was related to water temperature and nitrate concentration increases, both known to boost algal productivity. We supplemented our experiment with a regional survey collecting > 1450 flow-benthic algal measurements at streams varying in water abstraction levels. We confirmed the tipping point flow value, albeit at a slightly lower threshold (40-50%). A global literature review broadly confirmed our results with a mean tipping point at 58% of flow reduction. Our study provides robust in situ demonstrations of regime shift thresholds in running waters with potentially strong implications for environmental flows management.

Effects of Light and Temperature on the Metabolic Profiling of Two Habitat-Dependent Bloom-Forming Cyanobacteria

Rapid proliferation of cyanobacteria in both benthic and suspended (planktonic) habitats is a major threat to environmental safety, as they produce nuisance compounds such as cytotoxins and off-flavors, which degrade the safety and quality of water supplies. Temperature and light irradiance are two of the key factors in regulating the occurrence of algal blooms and production of major off-flavors. However, the role of these factors in regulating the growth and metabolism is poorly explored for both benthic and planktonic cyanobacteria. To fill this gap, we studied the effects of light and temperature on the growth and metabolic profiling of both benthic (Hapalosiphon sp. MRB220) and planktonic (Planktothricoides sp. SR001) environmental species collected from a freshwater reservoir in Singapore. Moreover, this study is the first report on the metabolic profiling of cyanobacteria belonging to two different habitats in response to altered environmental conditions. The highest growth rate of both species was observed at the highest light intensity (100 μmol photons/m²/s) and at a temperature of 33 °C. Systematic metabolite profiling analysis suggested that temperature had a more profound effect on metabolome of the Hapalosiphon, whereas light had a greater effect in the case of Planktothricoides. Interestingly, Planktothricoides sp. SR001 showed a specialized adaptation mechanism via biosynthesis of arginine, and metabolism of cysteine and methionine to survive and withstand higher temperatures of 38 °C and higher. Hence, the mode of strategies for coping with different light and temperature conditions was correlated with the growth and alteration in metabolic activities for physiological and ecological adaptations in both species. In addition, we putatively identified a number of unique metabolites with a broad range of antimicrobial activities in both species in response to both light and temperature. These metabolites could play a role in the dominant behavior of these species in suppressing competition during bloom formation. Overall, this study elucidated novel insights into the effects of environmental factors on the growth, metabolism, and adaptation strategies of cyanobacteria from two different habitats, and could be useful in controlling their harmful effects on human health and environmental concerns.

Benthic cyanobacteria: A utility-centred field study

Although there is growing evidence that benthic cyanobacteria represent a significant source of toxins and taste and odour (T&O) compounds in water bodies globally, water utilities rarely monitor for them. Benthic cyanobacteria grow in an array of matrices such as sediments, biofilms, and floating mats, and they can detach and colonize treatment plants. The occurrence of compounds produced by benthic species across matrix and climate types has not been systematically investigated. Consequently, there is a lack of guidance available to utilities to monitor for and mitigate the risk associated with benthic cyanobacteria. To assess toxin and T&O risk across climatic zones and provide guidance to water utilities for the monitoring of benthic mats, two field surveys were conducted across three continents. The surveys examined the occurrence of six secondary metabolites and associated genes, namely, geosmin, 2-methylisoborneol (MIB), anatoxin-a, saxitoxin, microcystin, and cylindrospermopsin, in benthic environmental samples collected across three climates (i.e., temperate, sub-tropical, and tropical) and a range of matrix types. Existing enzyme-linked immunosorbent assays (ELISAs) and qPCR assays and were used to measure compound concentrations and their associated genes in samples. A novel qPCR assay was designed to differentiate the production of MIB by actinobacteria from that of cyanobacteria. MIB occurrence was higher in warmer climates than temperate climates. Cyanobacteria in benthic mats were the major producers of taste and odour compounds. Floating mats contained significantly higher concentrations of geosmin and saxitoxins compared to other matrix types. Samples collected in warmer areas contained significantly more saxitoxin and cylindrospermopsin than samples collected in temperate climates. While these trends were mainly indicative, they can be used to establish monitoring practices. These surveys demonstrate that benthic mats are significant contributors of secondary metabolites in source water and should be monitored accordingly. Benthic cyanobacteria were the sole producers of T&O in up to 17% of the collected samples compared to actinobacteria, which were sole producers in only 1% of the samples. The surveys also provided a platform of choice for the transfer of methodologies and specific knowledge to participating utilities to assist with the establishment of monitoring practices for benthic cyanobacteria and associated secondary metabolites.

Development of a Risk Characterization Tool for Harmful Cyanobacteria Blooms on the Ohio River

A data-driven approach to characterizing the risk of cyanobacteria-based harmful algal blooms (cyanoHABs) was undertaken for the Ohio River. Twenty-five years of river discharge data were used to develop Bayesian regression models that are currently applicable to 20 sites spread-out along the entire 1579 km of the river’s length. Two site-level prediction models were developed based on the antecedent flow conditions of the two blooms that occurred on the river in 2015 and 2019: one predicts if the current year will have a bloom (the occurrence model), and another predicts bloom persistence (the persistence model). Predictors for both models were based on time-lagged average flow exceedances and a site’s characteristic residence time under low flow conditions. Model results are presented in terms of probabilities of occurrence or persistence with uncertainty. Although the occurrence of the 2019 bloom was well predicted with the modeling approach, the limited number of events constrained formal model validation. However, as a measure of performance, leave-one-out cross validation returned low misclassification rates, suggesting that future years with flow time series like the previous bloom years will be correctly predicted and characterized for persistence potential. The prediction probabilities are served in real time as a component of a risk characterization tool/web application. In addition to presenting the model’s results, the tool was designed with visualization options for studying water quality trends among eight river sites currently collecting data that could be associated with or indicative of bloom conditions. The tool is made accessible to river water quality professionals to support risk communication to stakeholders, as well as serving as a real-time water data monitoring utility.

Mapping Benthic Algae and Cyanobacteria in River Channels from Aerial Photographs and Satellite Images: A Proof-of-Concept Investigation on the Buffalo National River, AR, USA

Although rivers are of immense practical, aesthetic, and recreational value, these aquatic habitats are particularly sensitive to environmental changes. Increasingly, changes in streamflow and water quality are resulting in blooms of bottom-attached (benthic) algae, also known as periphyton, which have become widespread in many water bodies of US national parks. Because these blooms degrade visitor experiences and threaten human and ecosystem health, improved methods of characterizing benthic algae are needed. This study evaluated the potential utility of remote sensing techniques for mapping variations in algal density in shallow, clear-flowing rivers. As part of an initial proof-of-concept investigation, field measurements of water depth and percent cover of benthic algae were collected from two reaches of the Buffalo National River along with aerial photographs and multispectral satellite images. Applying a band ratio algorithm to these data yielded reliable depth estimates, although a shallow bias and moderate level of precision were observed. Spectral distinctions among algal percent cover values ranging from 0 to 100% were subtle and became only slightly more pronounced when the data were aggregated to four ordinal levels. A bagged trees machine learning model trained using the original spectral bands and image-derived depth estimates as predictor variables was used to produce classified maps of algal density. The spatial and temporal patterns depicted in these maps were reasonable but overall classification accuracies were modest, up to 64.6%, due to a lack of spectral detail. To further advance remote sensing of benthic algae and other periphyton, future studies could adopt hyperspectral approaches and more quantitative, continuous metrics such as biomass.

Molecular and Pigment Analyses Provide Comparative Results When Reconstructing Historic Cyanobacterial Abundances from Lake Sediment Cores

Understanding the historical onset of cyanobacterial blooms in freshwater bodies can help identify their potential drivers. Lake sediments are historical archives, containing information on what has occurred in and around lakes over time. Paleolimnology explores these records using a variety of techniques, but choosing the most appropriate method can be challenging. We compared results obtained from a droplet digital PCR assay targeting a cyanobacterial-specific region of the 16S rRNA gene in sedimentary DNA and cyanobacterial pigments (canthaxanthin, echinenone, myxoxanthophyll and zeaxanthin) analysed using high-performance liquid chromatography in four sediment cores. There were strong positive relationships between the 16S rRNA gene copy concentrations and individual pigment concentrations, but relationships differed among lakes and sediment core depths within lakes. The relationships were more consistent when all pigments were summed, which we attribute to different cyanobacteria species, in different lakes, at different times producing different suites of pigments. Each method had benefits and limitations, which should be taken into consideration during method selection and when interpreting paleolimnological data. We recommend this biphasic approach when making inferences about changes in the entire cyanobacterial community because they yielded complementary information. Our results support the view that molecular methods can yield results similar to traditional paleolimnological proxies when caveats are adequately addressed.

A critical review on operation and performance of source water control strategies for cyanobacterial blooms: Part I-chemical control methods

Cyanobacterial blooms produce nuisance metabolites (e.g., cyanotoxins and T&O compounds) thereby posing water quality management issues for aquatic sources used for potable water production, aquaculture, and recreation. A variety of in-lake/reservoir control measures are implemented to reduce the abundance of nuisance cyanobacteria biomass or decrease the amount of available phosphorous (P). This paper critically reviews the chemical control strategies implemented for in-lake/reservoir management of cyanobacterial blooms, i.e., algaecides and nutrient sequestering coagulants/flocculants, by highlighting (i) their mode of action, (ii) cases of successful and unsuccessful treatment, (iii) and factors influencing performance (e.g., water quality, process control techniques, source water characteristics, etc.). Algaecides generally result in immediate improvements in water quality and offer selective cyanobacterial control when peroxide-based alagecides are used. However, they have a range of limitations: causing cell lysis and release of cyanotoxins, posing negative impacts on aquatic plants and animals, leaving behind environmentally relevant treatment residuals (e.g., Cu in water and sediments), and offering only short-term bloom control characterized by cyanobacterial rebound. Coagulants/flocculants (alum, iron, calcium, and lanthanum bentonite) offer long-term internal nutrient control when external nutrient loading is controlled. Treatment performance is often influenced by background water quality conditions, and source water characteristics (e.g., surface area, depth, mixing regimes, and residence time). The reviewed case studies highlight that external nutrient load reduction is the most fundamental aspect of cyanobacterial control. None of the reviewed control strategies provide a comprehensive solution to cyanobacterial blooms.

Genome Streamlining, Plasticity, and Metabolic Versatility Distinguish Co-occurring Toxic and Nontoxic Cyanobacterial Strains of Microcoleus

Harmful cyanobacterial bloom occurrences have increased worldwide due to climate change and eutrophication, causing nuisance and animal deaths. Species from the benthic cyanobacterial genus Microcoleus are ubiquitous and form thick mats in freshwater systems, such as rivers, that are sometimes toxic due to the production of potent neurotoxins (anatoxins). Anatoxin-producing (toxic) strains typically coexist with non-anatoxin-producing (nontoxic) strains in mats, although the reason for this is unclear. To determine the genetic mechanisms differentiating toxic and nontoxic Microcoleus, we sequenced and assembled genomes from 11 cultures and compared these to another 31 Microcoleus genomes. Average nucleotide identities (ANI) indicate that toxic and nontoxic strains are distinct species (ANI, <95%), and only 6% of genes are shared across all 42 genomes, suggesting a high level of genetic divergence among Microcoleus strains. Comparative genomics showed substantial genome streamlining in toxic strains and a potential dependency on external sources for thiamine and sucrose. Toxic and nontoxic strains are further differentiated by an additional set of putative nitrate transporter (nitrogen uptake) and cyanophycin (carbon and nitrogen storage) genes, respectively. These genes likely confer distinct competitive advantages based on nutrient availability and suggest nontoxic strains are more robust to nutrient fluctuations. Nontoxic strains also possess twice as many transposable elements, potentially facilitating greater genetic adaptation to environmental changes. Our results offer insights into the divergent evolution of Microcoleus strains and the potential for cooperative and competitive interactions that contribute to the co-occurrence of toxic and nontoxic species within mats. IMPORTANCE Microcoleus autumnalis, and closely related Microcoleus species, compose a geographically widespread group of freshwater benthic cyanobacteria. Canine deaths due to anatoxin-a poisoning, following exposure to toxic proliferations, have been reported globally. While Microcoleus proliferations are on the rise, the mechanisms underpinning competition between, or coexistence of, toxic and nontoxic strains are unknown. This study identifies substantial genetic differences between anatoxin-producing and non-anatoxin-producing strains, pointing to reduced metabolic flexibility in toxic strains, and potential dependence on cohabiting nontoxic strains. Results provide insights into the metabolic and evolutionary differences between toxic and nontoxic Microcoleus, which may assist in predicting and managing aquatic proliferations.

Blue Waters, Green Bottoms: Benthic Filamentous Algal Blooms Are an Emerging Threat to Clear Lakes Worldwide

Nearshore (littoral) habitats of clear lakes with high water quality are increasingly experiencing unexplained proliferations of filamentous algae that grow on submerged surfaces. These filamentous algal blooms (FABs) are sometimes associated with nutrient pollution in groundwater, but complex changes in climate, nutrient transport, lake hydrodynamics, and food web structure may also facilitate this emerging threat to clear lakes. A coordinated effort among members of the public, managers, and scientists is needed to document the occurrence of FABs, to standardize methods for measuring their severity, to adapt existing data collection networks to include nearshore habitats, and to mitigate and reverse this profound structural change in lake ecosystems. Current models of lake eutrophication do not explain this littoral greening. However, a cohesive response to it is essential for protecting some of the world's most valued lakes and the flora, fauna, and ecosystem services they sustain.

Cyanobacteria and Cyanotoxins in a Changing Environment: Concepts, Controversies, Challenges

Concern is widely being published that the occurrence of toxic cyanobacteria is increasing in consequence of climate change and eutrophication, substantially threatening human health. Here, we review evidence and pertinent publications to explore in which types of waterbodies climate change is likely to exacerbate cyanobacterial blooms; whether controlling blooms and toxin concentrations requires a balanced approach of reducing not only the concentrations of phosphorus (P) but also those of nitrogen (N); how trophic and climatic changes affect health risks caused by toxic cyanobacteria. We propose the following for further discussion: (i) Climate change is likely to promote blooms in some waterbodies—not in those with low concentrations of P or N stringently limiting biomass, and more so in shallow than in stratified waterbodies. Particularly in the latter, it can work both ways—rendering conditions for cyanobacterial proliferation more favourable or less favourable. (ii) While N emissions to the environment need to be reduced for a number of reasons, controlling blooms can definitely be successful by reducing only P, provided concentrations of P can be brought down to levels sufficiently low to stringently limit biomass. Not the N:P ratio, but the absolute concentration of the limiting nutrient determines the maximum possible biomass of phytoplankton and thus of cyanobacteria. The absolute concentrations of N or P show which of the two nutrients is currently limiting biomass. N can be the nutrient of choice to reduce if achieving sufficiently low concentrations has chances of success. (iii) Where trophic and climate change cause longer, stronger and more frequent blooms, they increase risks of exposure, and health risks depend on the amount by which concentrations exceed those of current WHO cyanotoxin guideline values for the respective exposure situation. Where trophic change reduces phytoplankton biomass in the epilimnion, thus increasing transparency, cyanobacterial species composition may shift to those that reside on benthic surfaces or in the metalimnion, changing risks of exposure. We conclude that studying how environmental changes affect the genotype composition of cyanobacterial populations is a relatively new and exciting research field, holding promises for understanding the biological function of the wide range of metabolites found in cyanobacteria, of which only a small fraction is toxic to humans. Overall, management needs case-by-case assessments focusing on the impacts of environmental change on the respective waterbody, rather than generalisations.

Florida’s Harmful Algal Bloom (HAB) Problem: Escalating Risks to Human, Environmental and Economic Health With Climate Change

Harmful Algal Blooms (HABs) pose unique risks to the citizens, stakeholders, visitors, environment and economy of the state of Florida. Florida has been historically subjected to reoccurring blooms of the toxic marine dinoflagellate Karenia brevis (C. C. Davis) G. Hansen &amp; Moestrup since at least first contact with explorers in the 1500’s. However, ongoing immigration of more than 100,000 people year–1 into the state, elevated population densities in coastal areas with attendant rapid, often unregulated development, coastal eutrophication, and climate change impacts (e.g., increasing hurricane severity, increases in water temperature, ocean acidification and sea level rise) has likely increased the occurrence of other HABs, both freshwater and marine, within the state as well as the number of people impacted by these blooms. Currently, over 75 freshwater, estuarine, coastal and marine HAB species are routinely monitored by state agencies. While only blooms of K. brevis, the dinoflagellate Pyrodinium bahamense (Böhm) Steidinger, Tester, and Taylor and the diatom Pseudo-nitzschia spp. have resulted in closure of commercial shellfish beds, other HAB species, including freshwater and marine cyanobacteria, pose either imminent or unknown risks to human, environmental and economic health. HAB related human health risks can be classified into those related to consumption of contaminated shellfish and finfish, consumption of or contact with bloom or toxin contaminated water or exposure to aerosolized HAB toxins. While acute human illnesses resulting from consumption of brevetoxin-, saxitoxin-, and domoic acid-contaminated commercial shellfish have been minimized by effective monitoring and regulation, illnesses due to unregulated toxin exposures, e.g., ciguatoxins and cyanotoxins, are not well documented or understood. Aerosolized HAB toxins potentially impact the largest number of people within Florida. While short-term (days to weeks) impacts of aerosolized brevetoxin exposure are well documented (e.g., decreased respiratory function for at-risk subgroups such as asthmatics), little is known of longer term (&gt;1 month) impacts of exposure or the risks posed by aerosolized cyanotoxin [e.g., microcystin, β-N-methylamino-L-alanine (BMAA)] exposure. Environmental risks of K. brevis blooms are the best studied of Florida HABs and include acute exposure impacts such as significant dies-offs of fish, marine mammals, seabirds and turtles, as well as negative impacts on larval and juvenile stages of many biota. When K. brevis blooms are present, brevetoxins can be found throughout the water column and are widespread in both pelagic and benthic biota. The presence of brevetoxins in living tissue of both fish and marine mammals suggests that food web transfer of these toxins is occurring, resulting in toxin transport beyond the spatial and temporal range of the bloom such that impacts of these toxins may occur in areas not regularly subjected to blooms. Climate change impacts, including temperature effects on cell metabolism, shifting ocean circulation patterns and changes in HAB species range and bloom duration, may exacerbate these dynamics. Secondary HAB related environmental impacts are also possible due to hypoxia and anoxia resulting from elevated bloom biomass and/or the decomposition of HAB related mortalities. Economic risks related to HABs in Florida are diverse and impact multiple stakeholder groups. Direct costs related to human health impacts (e.g., increased hospital visits) as well as recreational and commercial fisheries can be significant, especially with wide-spread sustained HABs. Recreational and tourism-based industries which sustain a significant portion of Florida’s economy are especially vulnerable to both direct (e.g., declines in coastal hotel occupancy rates and restaurant and recreational users) and indirect (e.g., negative publicity impacts, associated job losses) impacts from HABs. While risks related to K. brevis blooms are established, Florida also remains susceptible to future HABs due to large scale freshwater management practices, degrading water quality, potential transport of HABs between freshwater and marine systems and the state’s vulnerability to climate change impacts.

Monitoring, Managing, and Communicating Risk of Harmful Algal Blooms (HABs) in Recreational Resources across Canada

Globally, harmful algal blooms (HABs) are on the rise, as is evidence of their toxicity. The impacts associated with blooms, however, vary across Nation states, as do the strategies and protocols to assess, monitor, and manage their occurrence. In Canada, water quality guidelines are standardized nationally, but the management strategies for HABs are not. Here, we explore current strategies to understand how to better communicate risks associated with HABs to the public. Our team conducted an environmental scan on provincial and territorial government agency protocols around HABs. Results suggest that there are variations in the monitoring, managing, and communicating of risk to the public: British Columbia, Manitoba, New Brunswick, and Quebec have well-established inter-agency protocols, and most provinces report following federal guidelines for water quality. Notably, 3 northern territories have no HABs monitoring or management protocols in place. More populous provinces use a variety of information venues (websites, social media, on site postings, and radio) to communicate risks associated with HABs, whereas others' communications are limited. To induce more collaboration on HABs monitoring and management and reduce the associated risks, creating a coherent system with consistent messaging and inter-agency communication is suggested.

First insights into the impacts of benthic cyanobacterial mats on fish herbivory functions on a nearshore coral reef

Benthic cyanobacterial mats (BCMs) are becoming increasingly common on coral reefs. In Fiji, blooms generally occur in nearshore areas during warm months but some are starting to prevail through cold months. Many fundamental knowledge gaps about BCM proliferation remain, including their composition and how they influence reef processes. This study examined a seasonal BCM bloom occurring in a 17-year-old no-take inshore reef area in Fiji. Surveys quantified the coverage of various BCM-types and estimated the biomass of key herbivorous fish functional groups. Using remote video observations, we compared fish herbivory (bite rates) on substrate covered primarily by BCMs (> 50%) to substrate lacking BCMs (< 10%) and looked for indications of fish (opportunistically) consuming BCMs. Samples of different BCM-types were analysed by microscopy and next-generation amplicon sequencing (16S rRNA). In total, BCMs covered 51 ± 4% (mean ± s.e.m) of the benthos. Herbivorous fish biomass was relatively high (212 ± 36 kg/ha) with good representation across functional groups. Bite rates were significantly reduced on BCM-dominated substratum, and no fish were unambiguously observed consuming BCMs. Seven different BCM-types were identified, with most containing a complex consortium of cyanobacteria. These results provide insight into BCM composition and impacts on inshore Pacific reefs.

Potential applications of CRISPR/Cas for next-generation biomonitoring of harmful algae blooms: A review

Research on harmful algal and cyanobacterial blooms (HABs and CHABs) has risen dramatically due to their increasing global distribution, frequency, and intensity. These blooms jeopardize public health, ecosystem function, sustainability and can have negative economic impacts. Numerous monitoring programs have been established using light microscopy, liquid chromatography coupled to mass spectrometry (LC-MS), ELISA, and spectrophotometry to monitor HABs/CHABs outbreaks. Recently, DNA/RNA-based molecular methods have been integrated into these programs to replace or complement traditional methods through analyzing environmental DNA and RNA (eDNA/eRNA) with techniques such as quantitative polymerase chain reaction (qPCR), fluorescent in situ hybridization (FISH), sandwich hybridization assay (SHA), isothermal amplification methods, and microarrays. These have enabled the detection of rare or cryptic species, enhanced sample throughput, and reduced costs and the need for visual taxonomic expertise. However, these methods have limitations, such as the need for high capital investment in equipment or detection uncertainties, including determining whether organisms are viable. In this review, we discuss the potential of newly developed molecular diagnosis technology based on Clustered Regularly Interspaced Short Palindromic Repeats/Cas proteins (CRISPR/Cas), which utilizes the prokaryotic adaptative immune systems of bacteria and archaea. Cas12 and Cas13-based platforms can detect both DNA and RNA with attomolar sensitivity within an hour. CRISPR/Cas diagnostic is a rapid, inexpensive, specific, and ultrasensitive technology that, with some further development, will provide many new platforms that can be used for HABs/CHABs biomonitoring and research.