Cyanobacterial bioactive metabolites-A review of their chemistry and biology

Microbial Community Response to Granular Peroxide-Based Algaecide Treatment of a Cyanobacterial Harmful Algal Bloom in Lake Okeechobee, Florida (USA)

Cyanobacterial harmful algal blooms (cyanoHABs) occur in fresh water globally. These can degrade water quality and produce toxins, resulting in ecological and economic damages. Thus, short-term management methods (i.e., algaecides) are necessary to rapidly mitigate the negative impacts of cyanoHABs. In this study, we assess the efficacy of a hydrogen peroxide-based algaecide (PAK® 27) on a Microcystis dominated bloom which occurred within the Pahokee Marina on Lake Okeechobee, Florida, USA. We observed a significant reduction in chlorophyll a (96.81%), phycocyanin (93.17%), and Microcystis cell counts (99.92%), and a substantial reduction in microcystins (86.7%) 48 h after treatment (HAT). Additionally, there was a significant shift in bacterial community structure 48 HAT, which coincided with an increase in the relative abundance of photosynthetic protists. These results indicate that hydrogen peroxide-based algaecides are an effective treatment method for cyanoHAB control and highlight their effects on non-target microorganisms (i.e., bacteria and protists).

Cyanopeptolins and Anabaenopeptins Are the Dominant Cyanopeptides from Planktothrix Strains Collected in Canadian Lakes

Common bloom-forming cyanobacteria produce complex strain-specific mixtures of secondary metabolites. The beneficial and toxic properties of these metabolite mixtures have attracted both research and public health interest. The advancement of mass spectrometry-based platforms and metabolomics data processing has accelerated the identification of new metabolites and feature dereplication from microbial sources. The objective of this study was to use metabolomics data processing to decipher the intracellular cyanopeptide diversity of six Planktothrix strains collected from Canadian lakes. Data-dependent acquisition experiments were used to collect a non-targeted high-resolution mass spectrometry dataset. Principal component analysis and factor loadings were used to visualize cyanopeptide variation between strains and identified features contributing to the observed variation. GNPS molecular networking was subsequently used to show the diversity of cyanopeptides produced by the Planktothrix strains. Each strain produced a unique mixture of cyanopeptides, and a total of 225 cyanopeptides were detected. Planktothrix sp. CPCC 735 produced the most (n = 68) cyanopeptides, and P. rubescens CPCC 732 produced the fewest (n = 27). Microcystins and anabaenopeptins were detected from all strains. Cyanopeptolins, microviridins and aeruginosins were detected from five, four and two strains, respectively. Cyanopeptolin (n = 80) and anabaenopeptin (n = 61) diversity was the greatest, whereas microcystins (n = 21) were the least diverse. Interestingly, three of the P. rubescens strains had different cyanopeptide profiles, despite being collected from the same lake at the same time. This study highlights the diversity of cyanopeptides produced by Planktothrix and further hints at the underestimated cyanopeptide diversity from subpopulations of chemotypic cyanobacteria in freshwater lakes.

Metabolite profiling of plant growth promoting cyanobacteria-Anabaena laxa and Calothrix elenkinii, using untargeted metabolomics

The metabolite profiles of two plant growth promoting cyanobacteria-Anabaena laxa and Calothrix elenkinii, which serve as promising biofertilizers, and biocontrol agents were generated to investigate their agriculturally beneficial activities. Preliminary biochemical analyses, in terms of total chlorophyll, total proteins, and IAA were highest at 14 days after inoculation (DAI). In A. laxa 20-25% higher values of reducing sugars, than C. elenkinii at both 14 and 21 DAI were recorded. Carbon and nitrogen assimilating enzyme activities-phosphoenol pyruvate carboxylase (PEPC), carbonic anhydrase (CA), and glutamine synthetase (GS) were highest at 14 DAI, albeit, nitrate reductase (NR) activity was higher by 0.73-0.84-fold at 21 DAI. Untargeted GC-MS (Gas chromatography-Mass spectrometric) analysis of metabolite profiles of 21d-old cyanobacterial cultures and characterization using NIST mass spectral library illustrated that A. laxa recorded highest number of metabolite hits in three chemical classes namely amino acid and peptides, nucleotides, nucleosides and analogues, besides other organic compounds. Based on the pathway analysis of identified metabolites, both A. laxa, and C. elenkinii were enriched in metabolites involved in aminoacyl-tRNA biosynthesis, and amino acid metabolism pathways, particularly lactose and glutamic acid, which are important players in plant-microbe interactions. Correlation-based metabolite network illustrated distinct and significant differences in the metabolic machinery of A. laxa and C. elenkinii, highlighting their novel identity and enrichment in C-N rich metabolites, as factors underlying their plant growth and soil fertility enhancing attributes, which make them valuable as inoculants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03902-7.

Effects of Harmful Cyanobacteria on Drinking Water Source Quality and Ecosystems

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

Cyanotoxin Analysis of Air Samples from the Great Salt Lake

The Great Salt Lake in Utah is the largest saline lake in the Western hemisphere and one of the largest terminal lakes in the world. Situated at the eastern edge of the Great Basin, it is a remnant of the freshwater Lake Bonneville whose water level precipitously lowered about 12,000 years ago due to a natural break in Red Rock pass to the north. It contains a diverse assemblage of cyanobacteria which vary spatially dependent on salinity. In 1984, the waters of the Great Salt Lake occupied 8500 km2. Nearly four decades later, the waters occupy 2500 km2-a reduction in surface area of 71%. With predominantly westerly winds, there is a potential for the adjacent metropolitan residents to the east to be exposed to airborne cyanobacteria- and cyanotoxin-containing dust. During the summer and fall months of 2022, air and dried sediment samples were collected and assessed for the presence of BMAA which has been identified as a risk factor for ALS. Collection of air samples equivalent to a person breathing for 1 h resulted in BMAA and isomers being found in some air samples, along with their presence in exposed lakebed samples. There was no clear relationship between the presence of these toxins in airborne and adjacent lakebed samples, suggesting that airborne toxins may originate from diffuse rather than point sources. These findings confirm that continued low water levels in the Great Salt Lake may constitute an increasing health hazard for the 2.5 million inhabitants of communities along the Wasatch Front.

A Direct Analysis of β-N-methylamino-l-alanine Enantiomers and Isomers and Its Application to Cyanobacteria and Marine Mollusks

Of the wide variety of toxic compounds produced by cyanobacteria, the neurotoxic amino acid β-N-methylamino-l-alanine (BMAA) has attracted attention as a result of its association with chronic human neurodegenerative diseases such as ALS and Alzheimer's. Consequently, specific detection methods are required to assess the presence of BMAA and its isomers in environmental and clinical materials, including cyanobacteria and mollusks. Although the separation of isomers such as β-amino-N-methylalanine (BAMA), N-(2-aminoethyl)glycine (AEG) and 2,4-diaminobutyric acid (DAB) from BMAA has been demonstrated during routine analysis, a further compounding factor is the potential presence of enantiomers for some of these isomers. Current analytical methods for BMAA mostly do not discriminate between enantiomers, and the chiral configuration of BMAA in cyanobacteria is still largely unexplored. To understand the potential for the occurrence of D-BMAA in cyanobacteria, a chiral UPLC-MS/MS method was developed to separate BMAA enantiomers and isomers and to determine the enantiomeric configuration of endogenous free BMAA in a marine Lyngbya mat and two mussel reference materials. After extraction, purification and derivatization with N-(4-nitrophenoxycarbonyl)-l-phenylalanine 2-methoxyethyl ester ((S)-NIFE), both L- and D-BMAA were identified as free amino acids in cyanobacterial materials, whereas only L-BMAA was identified in mussel tissues. The finding of D-BMAA in biological environmental materials raises questions concerning the source and role of BMAA enantiomers in neurological disease.

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.

Spatiotemporal diversity and community structure of cyanobacteria and associated bacteria in the large shallow subtropical Lake Okeechobee (Florida, United States)

Lake Okeechobee is a large eutrophic, shallow, subtropical lake in south Florida, United States. Due to decades of nutrient loading and phosphorus rich sediments, the lake is eutrophic and frequently experiences cyanobacterial harmful algal blooms (cyanoHABs). In the past, surveys of the phytoplankton community structure in the lake have been conducted by morphological studies, whereas molecular based studies have been seldom employed. With increased frequency of cyanoHABs in Lake Okeechobee (e.g., 2016 and 2018 Microcystis-dominated blooms), it is imperative to determine the diversity of cyanobacterial taxa that exist within the lake and the limnological parameters that drive bloom-forming genera. A spatiotemporal study of the lake was conducted over the course of 1 year to characterize the (cyano)bacterial community structure, using 16S rRNA metabarcoding, with coincident collection of limnological parameters (e.g., nutrients, water temperature, major ions), and cyanotoxins. The objectives of this study were to elucidate spatiotemporal trends of community structure, identify drivers of community structure, and examine cyanobacteria-bacterial relationships within the lake. Results indicated that cyanobacterial communities within the lake were significantly different between the wet and dry season, but not between periods of nitrogen limitation and co-nutrient limitation. Throughout the year, the lake was primarily dominated by the picocyanobacterium Cyanobium. The bloom-forming genera Cuspidothrix, Dolichospermum, Microcystis, and Raphidiopsis were highly abundant throughout the lake and had disparate nutrient requirements and niches within the lake. Anatoxin-a, microcystins, and nodularins were detected throughout the lake across both seasons. There were no correlated (cyano)bacteria shared between the common bloom-forming cyanobacteria Dolichospermum, Microcystis, and Raphidiopsis. This study is the first of its kind to use molecular based methods to assess the cyanobacterial community structure within the lake. These data greatly improve our understanding of the cyanobacterial community structure within the lake and the physiochemical parameters which may drive the bloom-forming taxa within Lake Okeechobee.

Review of Marine Cyanobacteria and the Aspects Related to Their Roles: Chemical, Biological Properties, Nitrogen Fixation and Climate Change

Marine cyanobacteria are an ancient group of photosynthetic microbes dating back to 3.5 million years ago. They are prolific producers of bioactive secondary metabolites. Over millions of years, natural selection has optimized their metabolites to possess activities impacting various biological targets. This paper discusses the historical and existential records of cyanobacteria, and their role in understanding the evolution of marine cyanobacteria through the ages. Recent advancements have focused on isolating and screening bioactive compounds and their respective medicinal properties, and we also discuss chemical property space and clinical trials, where compounds with potential pharmacological effects, such as cytotoxicity, anticancer, and antiparasitic properties, are highlighted. The data have shown that about 43% of the compounds investigated have cytotoxic effects, and around 8% have anti-trypanosome activity. We discussed the role of different marine cyanobacteria groups in fixing nitrogen percentages on Earth and their outcomes in fish productivity by entering food webs and enhancing productivity in different agricultural and ecological fields. The role of marine cyanobacteria in the carbon cycle and their outcomes in improving the efficiency of photosynthetic CO2 fixation in the chloroplasts of crop plants, thus enhancing the crop plant's yield, was highlighted. Ultimately, climate changes have a significant impact on marine cyanobacteria where the temperature rises, and CO2 improves the cyanobacterial nitrogen fixation.

Cyanotoxins, biosynthetic gene clusters, and factors modulating cyanotoxin biosynthesis

Cyanobacterial harmful algal blooms (CHABs) are a global environmental concern that encompasses public health issues, water availability, and water quality owing to the production of various secondary metabolites (SMs), including cyanotoxins in freshwater, brackish water, and marine ecosystems. The frequency, extent, magnitude, and duration of CHABs are increasing globally. Cyanobacterial species traits and changing environmental conditions, including anthropogenic pressure, eutrophication, and global climate change, together allow cyanobacteria to thrive. The cyanotoxins include a diverse range of low molecular weight compounds with varying biochemical properties and modes of action. With the application of modern molecular biology techniques, many important aspects of cyanobacteria are being elucidated, including aspects of their diversity, gene-environment interactions, and genes that express cyanotoxins. The toxicological, environmental, and economic impacts of CHABs strongly advocate the need for continuing, extensive efforts to monitor cyanobacterial growth and to understand the mechanisms regulating species composition and cyanotoxin biosynthesis. In this review, we critically examined the genomic organization of some cyanobacterial species that lead to the production of cyanotoxins and their characteristic properties discovered to date.

Ecotoxicological assessment of guanitoxin-producing cyanobacteria in Danio rerio and Daphnia similis

Anthropogenic activity has dramatically deteriorated aquatic ecosystems in recent years. Such environmental alterations could change the primary producers' composition, exacerbating the proliferation of harmful microorganisms such as cyanobacteria. Cyanobacteria can produce several secondary metabolites, including guanitoxin, a potent neurotoxin and the only naturally occurring anticholinesterase organophosphate ever reported in the literature. Therefore, this study investigated the acute toxicity of guanitoxin-producing cyanobacteria Sphaerospermopsis torques-reginae (ITEP-024 strain) aqueous and 50% methanolic extracts in zebrafish (Danio rerio) hepatocytes (ZF-L cell line), zebrafish embryos (fish embryo toxicity - FET) and specimens of the microcrustacean Daphnia similis. For this, hepatocytes were exposed to 1-500 mg/L of the ITEP-024 extracts for 24 h, the embryos to 31.25-500 mg/L for 96 h, and D. similis to 10-3000 mg/L for 48 h. Non-target metabolomics was also performed to analyze secondary metabolites produced by the ITEP-024 using LC-MS/MS. Metabolomics indicated the guanitoxin presence just in the aqueous extract of the ITEP-024 and the presence of the cyanopeptides namalides, spumigins, and anabaenopeptins in the methanolic extract. The aqueous extract decreased the viability of zebrafish hepatocytes (EC(I)_50(24h) = 366.46 mg/L), and the methanolic extract was not toxic. FET showed that the aqueous extract (LC₅₀₍₉₆₎ = 353.55 mg/L) was more toxic than the methanolic extract (LC₅₀₍₉₆₎ = 617.91 mg/L). However, the methanolic extract had more sublethal effects, such as abdominal and cardiac (cardiotoxicity) edema and deformation (spinal curvature of the larvae). Both extracts immobilized daphnids at the highest concentration analyzed. However, the aqueous extract was nine times more lethal (EC(I)_50(48h) = 108.2 mg/L) than the methanolic extract (EC(I)_50(48h) = 980.65 mg/L). Our results showed an imminent biological risk for aquatic fauna living in an ecosystem surrounded by ITEP-024 metabolites. Our findings thus highlight the urgency of understanding the effects of guanitoxin and cyanopeptides in aquatic animals.

Metabolomics Reveals Strain-Specific Cyanopeptide Profiles and Their Production Dynamics in Microcystis aeruginosa and M. flos-aquae

Cyanobacterial blooms that release biologically active metabolites into the environment are increasing in frequency as a result of the degradation of freshwater ecosystems globally. The microcystins are one group of cyanopeptides that are extensively studied and included in water quality risk management frameworks. Common bloom-forming cyanobacteria produce incredibly diverse mixtures of other cyanopeptides; however, data on the abundance, distribution, and biological activities of non-microcystin cyanopeptides are limited. We used non-targeted LC-MS/MS metabolomics to study the cyanopeptide profiles of five Microcystis strains: four M. aeruginosa and one M. flos-aquae. Multivariate analysis and GNPS molecular networking demonstrated that each Microcystis strain produced a unique mixture of cyanopeptides. In total, 82 cyanopeptides from the cyanopeptolin (n = 23), microviridin (n = 18), microginin (n = 12), cyanobactin (n = 14), anabaenopeptin (n = 6), aeruginosin (n = 5), and microcystin (n = 4) classes were detected. Microcystin diversity was low compared with the other detected cyanopeptide classes. Based on surveys of the literature and spectral databases, most cyanopeptides represented new structures. To identify growth conditions yielding high amounts of multiple cyanopeptide groups, we next examined strain-specific cyanopeptide co-production dynamics for four of the studied Microcystis strains. When strains were cultivated in two common Microcystis growth media (BG-11 and MA), the qualitative cyanopeptides profiles remained unchanged throughout the growth cycle. For each of the cyanopeptide groups considered, the highest relative cyanopeptide amounts were observed in the mid-exponential growth phase. The outcomes of this study will guide the cultivation of strains producing common and abundant cyanopeptides contaminating freshwater ecosystems. The synchronous production of each cyanopeptide group by Microcystis highlights the need to make more cyanopeptide reference materials available to investigate their distributions and biological functions.

Co-Occurrence of Taste and Odor Compounds and Cyanotoxins in Cyanobacterial Blooms: Emerging Risks to Human Health?

Cyanobacteria commonly form large blooms in waterbodies; they can produce cyanotoxins, with toxic effects on humans and animals, and volatile compounds, causing bad tastes and odors (T&O) at naturally occurring low concentrations. Notwithstanding the large amount of literature on either cyanotoxins or T&O, no review has focused on them at the same time. The present review critically evaluates the recent literature on cyanotoxins and T&O compounds (geosmin, 2-methylisoborneol, β-ionone and β-cyclocitral) to identify research gaps on harmful exposure of humans and animals to both metabolite classes. T&O and cyanotoxins production can be due to the same or common to different cyanobacterial species/strains, with the additional possibility of T&O production by non-cyanobacterial species. The few environmental studies on the co-occurrence of these two groups of metabolites are not sufficient to understand if and how they can co-vary, or influence each other, perhaps stimulating cyanotoxin production. Therefore, T&Os cannot reliably serve as early warning surrogates for cyanotoxins. The scarce data on T&O toxicity seem to indicate a low health risk (but the inhalation of β-cyclocitral deserves more study). However, no data are available on the effects of combined exposure to mixtures of cyanotoxins and T&O compounds and to combinations of T&O compounds; therefore, whether the co-occurrence of cyanotoxins and T&O compounds is a health issue remains an open question.

Interactions between chytrids cause variable infection strategies on harmful algal bloom forming species

Cyanobacteria have a great diversity of natural enemies, such as herbivores and pathogens, including fungal pathogens within the Chytridiomycota (chytrids). While these pathogens have been previously described on a select number of cyanobacterial hosts and are suspected to play a significant ecological role, little is understood about species interactions and how competition between parasites can affect epidemic development and bloom formation. Here, three Planktothrix agardhii isolates from Sandusky Bay, Lake Erie (OH, USA) were challenged in monoculture and polyculture against infection by three isolates (C1, C2, C10) of their obligate chytrid fungal pathogen, Rhizophydiales sp. The chytrid isolates were inoculated as single isolates or a mixture of up to three different isolates. In monoculture, host isolates were characterized as highly susceptible (P. agardhii 1030), moderately susceptible (P. agardhii 1808) or mostly resistant (P. agardhii 1801). Co-infection of chytrid isolates on the highly susceptible host isolate had an additive effect on chytrid prevalence, leading to a culture crash where 2 or 3 chytrid isolates were present. Co-infection of chytrid isolates on the moderately susceptible and mostly resistant isolates had no effect on chytrid infection outcome or prevalence compared to infection with a single isolate. In polyculture, the effect on host growth was most significant in the single chytrid isolate treatment, which was attenuated with the addition of mixed chytrid treatments. Genetic analysis of the resulting population after the experimental period showed a tendency for the chytrid isolate C1 and P. agardhii 1801 to dominate in mixed population samples. Two different interspecific interactions seem to be in play; varied parasite infection strategies allow for the amplification of infection prevalence due to mixed chytrids in a susceptible monoculture, or competition allows for the dominance of a single chytrid isolate in monoculture and the reduction of infection prevalence in a host polyculture. This work thus highlights how interactions between chytrid infections can change the course of epidemic development and harmful algal bloom formation.

Comparative metabolomic analysis of exudates of microcystin-producing and microcystin-free Microcystis aeruginosa strains

Cyanobacterial harmful algal blooms (cHABs) dominated by Microcystis aeruginosa threaten the ecological integrity and beneficial uses of lakes globally. In addition to producing hepatotoxic microcystins (MC), M. aeruginosa exudates (MaE) contain various compounds with demonstrated toxicity to aquatic biota. Previously, we found that the ecotoxicity of MaE differed between MC-producing and MC-free strains at exponential (E-phase) and stationary (S-phase) growth phases. However, the components in these exudates and their specific harmful effects were unclear. In this study, we performed untargeted metabolomics based on liquid chromatography-mass spectrometry to reveal the constituents in MaE of a MC-producing and a MC-free strain at both E-phase and S-phase. A total of 409 metabolites were identified and quantified based on their relative abundance. These compounds included lipids, organoheterocyclic compounds, organic acid, benzenoids and organic oxygen compounds. Multivariate analysis revealed that strains and growth phases significantly influenced the metabolite profile. The MC-producing strain had greater total metabolites abundance than the MC-free strain at S-phase, whereas the MC-free strain released higher concentrations of benzenoids, lipids, organic oxygen, organic nitrogen and organoheterocyclic compounds than the MC-producing strain at E-phase. Total metabolites had higher abundance in S-phase than in E- phase in both strains. Analysis of differential metabolites (DMs) and pathways suggest that lipids metabolism and biosynthesis of secondary metabolites were more tightly coupled to growth phases than to strains. Abundance of some toxic lipids and benzenoids DMs were significantly higher in the MC-free strain than the MC-producing one. This study builds on the understanding of MaE chemicals and their biotoxicity, and adds to evidence that non-MC-producing strains of cyanobacteria may also pose a threat to ecosystem health.

Untargeted and targeted LC-MS and data processing workflow for the comprehensive analysis of oligopeptides from cyanobacteria

Cyanobacteria produce a plethora of structurally diverse bioactive secondary metabolites, including cyanotoxins which pose a serious threat to humans and other living organisms worldwide. Currently, a wide variety of mass spectrometry-based methods for determination of microcystins (MCs), the most commonly occurring and studied class of cyanotoxins, have been developed and employed for research and monitoring purposes. The scarcity of commercially available reference materials, together with the ever-growing range of mass spectrometers and analytical approaches, make the accuracy of quantitative analyses a critical point to be carefully investigated in view of a reliable risk evaluation. This study reports, a comparative investigation of the qualitative and quantitative MCs profile obtained using targeted and untargeted liquid chromatography-mass spectrometry approaches for the analyses of cyanobacterial biomass from Lake Kastoria, Greece. Comparison of the total MCs content measured by the two approaches showed good correlation, with variations in the range of 3.8-13.2%. In addition, the implementation of an analytical workflow on a hybrid linear ion trap/orbitrap mass spectrometer is described, based on combining data-dependent acquisition and a powerful database of cyanobacterial metabolites (CyanoMetDB) for the annotation of known and discovery of new cyanopeptides. This untargeted strategy proved highly effective for the identification of MCs, microginins, anabaenopeptins, and micropeptins. The systematic interpretation of the acquired fragmentation patterns allowed the elucidation of two new MC structural variants, MC-PrhcysR and MC-Prhcys(O)R, and proposal of structures for two new microginins, isomeric cyanostatin B and MG 821A, and three isomeric micropeptins at m/z 846.4715, 846.4711 and 846.4723.

Biomedical Applications of Biosynthesized Gold Nanoparticles from Cyanobacteria: an Overview

Recently there had been a great interest in biologically synthesized nanoparticles (NPs) as potential therapeutic agents. The shortcomings of conventional non-biological synthesis methods such as generation of toxic byproducts, energy consumptions, and involved cost have shifted the attention towards green syntheses of NPs. Among noble metal NPs, gold nanoparticles (AuNPs) are the most extensively used ones, owing to the unique physicochemical properties. AuNPs have potential therapeutic applications, as those are synthesized with biomolecules as reducing and stabilizing agent(s). The green method of AuNP synthesis is simple, eco-friendly, non-toxic, and cost-effective with the use of renewable energy sources. Among all taxa, cyanobacteria have attracted considerable attention as nano-biofactories, due to cellular uptake of heavy metals from the environment. The cellular bioactive pigments, enzymes, and polysaccharides acted as reducing and coating agents during the process of biosynthesis. However, cyanobacteria-mediated AuNPs have potential biomedical applications, namely, targeted drug delivery, cancer treatment, gene therapy, antimicrobial agent, biosensors, and imaging.

Microcystis sp. AE03 strain in Dal Lake harbors cylindrospermopsin and microcystin synthetase gene cluster

Cyanobacterial harmful algal blooms (CHABs) are increasing at an alarming rate in different water bodies worldwide. In India, CHAB events in water bodies such as Dal Lake have been sporadically reported with no study done to characterize the cyanobacterial species and their associated toxins. We hypothesized that this Lake is contaminated with toxic cyanobacterial species with the possibility of the presence of cyanotoxin biosynthetic genes. We, therefore, used some of the molecular tools such as 16S ribosomal DNA, PCR, and phylogenetic analysis to explore cyanobacterial species and their associated toxins. A 3-year (2018–2020) survey was conducted at three different sampling sites of Dal Lake namely, Grand Palace Gath (S1), Nigeen basin (S2), and Gagribal basin (S3). Two strains of Dolichospermum sp. AE01 and AE02 (S3 and S1 site) and one strain of Microcystis sp. AE03 (S2 site) was isolated, cultured, and characterized phylogenetically by 16S ribosomal DNA sequencing. The presence of cyanotoxin genes from the isolates was evaluated by PCR of microcystins (mcyB), anatoxins (anaC), and cylindrospermopsins (pks) biosynthesis genes. Results revealed the presence of both mcyB and pks gene in Microcystis sp. AE03, and only anaC gene in Dolichospermum sp. AE02 strain. However, Dolichospermum sp. AE01 strain was not found to harbor any such genes. Our findings, for the first time, reported the coexistence of pks and mcyB in a Microcystis AE03 strain. This study has opened a new door to further characterize the unexplored cyanobacterial species, their associated cyanotoxin biosynthetic genes, and the intervention of high-end proteomic techniques to characterize the cyanotoxins.

The Impact of Cyanobacteria Blooms on the Aquatic Environment and Human Health

Cyanobacteria blooms are a global aquatic environment problem. In recent years, due to global warming and water eutrophication, the surface cyanobacteria accumulate in a certain area to form cyanobacteria blooms driven by wind. Cyanobacteria blooms change the physical and chemical properties of water and cause pollution. Moreover, cyanobacteria release organic matter, N (nitrogen) and P (phosphorus) into the water during their apoptosis, accelerating the eutrophication of the water, threatening aquatic flora and fauna, and affecting the community structure and abundance of microorganisms in the water. Simultaneously, toxins and carcinogens released from cyanobacteria can be enriched through the food chain/web, endangering human health. This study summarized and analyzed the research of the influence of cyanobacteria blooms on the aquatic environment and human health, which is helpful to understand further the harm of cyanobacteria blooms and provide some reference for a related research of cyanobacteria blooms.

Cyanopeptides restriction and degradation co-mediate microbiota assembly during a freshwater cyanobacterial harmful algal bloom (CyanoHAB)

Cyanobacterial harmful algal blooms (CyanoHABs) are globally intensifying and exacerbated by climate change and eutrophication. However, microbiota assembly mechanisms underlying CyanoHABs remain elusive. Especially, cyanopeptides, as a group of bioactive secondary metabolites of cyanobacteria, could affect microbiota assembly and ecosystem function. Here, the trajectory of cyanopeptides was followed and linked to microbiota during Microcystis-dominated CyanoHABs in Lake Taihu, China. The most abundant cyanopeptide classes detected included microginin, spumigin, microcystin, nodularin and cyanopeptolin with total MC-LR-equivalent concentrations between 0.23 and 2051.54 ppb, of which cyanotoxins beyond microcystins (e.g., cyanostatin B and nodularin_R) far exceeded reported organismal IC₅₀ and negatively correlated with microbiota diversity, exerting potential collective eco-toxicities stronger than microcystins alone. The microbial communities were differentiated by size fraction and sampling date throughout CyanoHABs, and surprisingly, their variances were better explained by cyanopeptides (19-38%) than nutrients (0-16%). Cyanopeptides restriction (e.g., inhibition) and degradation were first quantitatively verified as the deterministic drivers governing community assembly, with stochastic processes being associated with the interplay between cyanopeptide dynamics and lake microbiota. This study presents an emerging paradigm in which cyanopeptides restriction and degradation co-mediate lake water microbiota assembly, unveiling new insights into the ecotoxicological significance of CyanoHABs to freshwater ecosystems.

The Effects of Algaecides and Herbicides on a Nuisance Microcystis wesenbergii-Dominated Bloom

Microcystis-dominated cyanobacterial harmful algal blooms (cyanoHABs) are a reoccurring problem globally, resulting in widespread economic and health impacts. As public awareness of the risks of blooms increases, there is an urgent need for studies on both short-term and long-term management of cyanoHABs. In order to provide science-based best management practices and treatment options, we tested various concentrations and combinations of USEPA-registered algaecides and herbicides on a Microcystis wesenbergii-dominated bloom. The bloom material was exposed to fifteen different algaecides, herbicides, or combinations, using four different concentrations. Cell abundance and morphology as well as microscopic analyses were undertaken at the time of collection and 72 h post-treatment. Overall, the effectiveness of the chemicals varied with the most efficacious treatments being SeClear®, and a combination of Hydrothol® 191 and GreenClean® Liquid 5.0, both of which resulted in a significant decrease at all tested concentrations after 72 h. Interestingly, Microcystis wesenbergii is more resistant to algaecides than M. aeruginosa. Results from this study provide valuable data for treating cyanoHABs and show the varied efficacy of different algaecidal formulations.

Inhibition of Filamentous Thermosensitive Mutant-Z Protein in Bacillus subtilis by Cyanobacterial Bioactive Compounds

Antibiotic resistance is one of the major growing concerns for public health. Conventional antibiotics act on a few predefined targets and, with time, several bacteria have developed resistance against a large number of antibiotics. The WHO has suggested that antibiotic resistance is at a crisis stage and identification of new antibiotics and targets could be the only approach to bridge the gap. Filamentous Temperature Sensitive-Mutant Z (Fts-Z) is one of the promising and less explored antibiotic targets. It is a highly conserved protein and plays a key role in bacterial cell division by introducing a cytokinetic Z-ring formation. In the present article, the potential of over 165 cyanobacterial compounds with reported antibiotic activity against the catalytic core domain in the Fts-Z protein of the Bacillus subtilis was studied. The identified cyanobacterial compounds were screened using the GLIDE module of Maestro v-2019-2 followed by 100-ns molecular dynamics (MD) simulation. Ranking of the potential compound was performed using dock score and MMGBSA based free energy. The study reported that the docking score of aphanorphine (−6.010 Kcalmol⁻¹) and alpha-dimorphecolic acid (ADMA) (−6.574 Kcalmol⁻¹) showed significant role with respect to the reported potential inhibitor PC190723 (−4.135 Kcalmol⁻¹). A 100 ns MD simulation infers that Fts-Z ADMA complex has a stable conformation throughout the progress of the simulation. Both the compounds, i.e., ADMA and Aphanorphine, were further considered for In-vitro validation by performing anti-bacterial studies against B. subtilis by agar well diffusion method. The results obtained through In-vitro studies confirm that ADMA, a small molecule of cyanobacterial origin, is a potential compound with an antibacterial activity that may act by inhibiting the novel target Fts-Z and could be a great drug candidate for antibiotic development.

Cyanobacterial cell-wall components as emerging environmental toxicants - detection and holistic monitoring by cellular signaling biosensors

Cyanobacterial blooms constitute a recognized danger to aquatic environment and public health not only due to presence of main group of cyanotoxins, such as microcystins, cylindrospermopsin or anatoxin-a, but also other emerging bioactivities. An innovative approach identifying such bioactivities is the application of cellular biosensors based on reporter genes which detect the impact of cyanobacterial cells and components on actual human cells in a physiological-like setting. In the present study biosensor cell lines detecting four different types of bioactivities (ARE - oxidative stress, NFKBRE - immunomodulatory pathogen-associated molecular patterns, AHRE - persistent organic pollutants, GRE - endocrine disruptors) were exposed to concentrated cyanobacterial cells from 21 environmental bloom samples and from eight cultures (Microcystis aeruginosa, Aphanizomenon flos-aquae, Planktothrix agardhii and Raphidiopsis raciborskii). The AHRE and GRE biosensors did not detect any relevant bioactivity. In turn, ARE biosensors were significantly activated by bloom samples from Jeziorsko (180-250%) and Sulejów (250-400%) reservoirs with the highest cyanobacterial biomass, while activation by cultures was weak/undetectable. The same biosensors were stimulated by microcystin-LR (250%) and anatoxin-a (150%). The NFKBRE biosensors were activated to varying extent (140-650%) by most bloom and culture samples, pointing to potential immunomodulatory toxic effects on humans. Lipopolysaccharide and lipoproteins were identified as responsible for NFKBRE activation (probably via pattern recognition receptors), while peptidoglycan had no bioactivity in this assay. Thus, the holistic approach to sample analysis with the application of cellular biosensors geared towards 4 separate pathways/bioactivities was validated for identification of novel bioactivities in organisms with recognized public health significance (e.g. this study is the first to describe cyanobacterial lipoproteins as potential environmental immunomodulators). Moreover, the ability of cellular biosensors to be activated by intact cyanobacterial cells from blooms provides proof of concept of their direct application for environmental monitoring, especially comparison of potential threats without need for chemical analysis and identification of toxicants.

Identification of Novel Microcystins Using High-Resolution MS and MSn with Python Code

Cyanotoxins called microcystins (MCs) are highly toxic and can be present in drinking water sources. Determining the structure of MCs is paramount because of its effect on toxicity. Though over 300 MC congeners have been discovered, many remain unidentified. Herein, a method is described for the putative identification of MCs using liquid chromatography (LC) coupled with high-resolution (HR) Orbitrap mass spectrometry (MS) and a new bottom-up sequencing strategy. Maumee River water samples were collected during a harmful algal bloom and analyzed by LC-MS with simultaneous HRMS and MS/MS. Unidentified ions with characteristic MC fragments (135 and 213 m/z) were recognized as possible novel MC congeners. An innovative workflow was developed for the putative identification of these ions. Python code was written to generate the potential structures of unidentified MCs and to assign ions after the fragmentation for structural confirmation. The workflow enabled the putative identification of eight previously reported MCs for which standards are not available and two newly discovered congeners, MC-HarR and MC-E(OMe)R.

Novel high throughput sequencing - fluorometric approach demonstrates Microcystis blooms across western Lake Erie are promoted by grazing resistance and nutrient enhanced growth

Cyanobacterial harmful algal blooms (CHABs) are a global public health threat. While CHABs are often promoted by nutrients, an important and often overlooked influence on bloom dynamics is zooplankton grazing. In the present study, zooplankton grazing and nutrient enrichment experiments were combined with next generation sequencing and fluorometric analyses to quantify differential grazing and nutrient effects on specific cyanobacterial genera across the western basin of Lake Erie. Grazing by two different sized daphnids, Daphnia magna and Daphnia pulex, was compared to protozooplankton grazing effects assessed via a dilution approach at sites within the Maumee and Sandusky Bays where Planktothrix, Microcystis, Synechococcus, and Dolichospermum were the dominant genera. Daphnid grazing significantly reduced Synechococcus net growth rates at most sites as well as Planktothrix net growth in Sandusky Bay and Dolichospermum in Maumee Bay. Dilution resulted in significant growth increase of Synechococcus at half of the sites and Planktothrix at most sites evidencing substantial grazing pressure by the protozooplankton community on these genera. In contrast, Microcystis populations were largely unaffected by daphnids and protozooplankton grazing but benefitted from nutrient enrichment more than other CHAB genera. When diatoms were present in moderate abundance, grazing rates by daphnids on diatoms were significantly greater than grazing rates on cyanobacteria. The novel approach used in this study established differences in grazing pressure and nutrient effects on differing taxa and revealed that, while many taxa were grazed by multiple classes of zooplankton (e.g. Planktothrix, Synechococcus, Dolichospermum, diatoms), the lack of grazing pressure on Microcystis coupled with nutrient-enhanced growth in western Lake Erie promotes the occurrence of CHABs of this genus.

Diversity of bioactive compound content across 71 genera of marine, freshwater, and terrestrial cyanobacteria

Cyanobacterial blooms have increased in frequency, distribution, and intensity due to climate change and anthropogenic nutrient input. The release of bioactive compounds accumulated in these blooms can affect the health of humans and the environment. The co-occurrence of bioactive metabolites is well-documented in bloom samples from marine and freshwater ecosystems, with fewer reports from unialgal isolates. Cyanobacteria also are important terrestrial ecosystem components, especially in drylands, but reports on bioactive molecules from terrestrial cyanobacteria are sparse. This study determined bioactive metabolite profiles for 71 genera of cyanobacteria from seven orders isolated from freshwater (12 genera), marine (15 genera), and terrestrial (44 genera) habitats originally. Cultures were harvested for bioactive metabolites when entering the late-exponential phase for all 157 strains, and 33 were sampled at both early and late exponential phases. Bioactive metabolites were analyzed using an ultra high performance/pressure liquid chromatography in-line with a time-of-flight mass spectrometer. Overall, 12 bioactive classes of the 28 identified were ubiquitous in all samples. On average, each freshwater genus produced ∼12 bioactive classes, whereas each marine genus contained > 4 bioactive classes, and each terrestrial genus contained ∼6 bioactive classes. While 10 of 12 freshwater genera produced at least 10 bioactive classes, only a single genus each from marine and terrestrial habitats had the same number of bioactive classed accumulated. Aeruginosin was found in 58 of 71 total genera, carmabin in 51 of 71 genera, and anabaenopeptin in 48 of 71 genera. Chemotaxonomic use of these secondary metabolites may help resolve higher-level genetic classification(s). An additional growth curve experiment showed that bioactive metabolites were produced at both early and late exponential growth phases. The bioactive metabolite accumulation pattern between early and late exponential phases differed by bioactive classes, genera, and habitats. This survey of 55 bioactive classes in cyanobacteria isolated from freshwater, marine, and terrestrial habitats (71 genera) provides as one of the first systematic bioactive metabolite profiles for cyanobacteria, which should be useful in environmental and drinking water management. Further, it offers novel insights about the toxin potential of selected terrestrial cyanobacteria.

Can Alkyl Quaternary Ammonium Cations Substitute H2O2 in Controlling Cyanobacterial Blooms-Laboratory and Mesocosm Studies

Mitigation of harmful cyanobacterial blooms that constitute a serious threat to water quality, particularly in eutrophic water, such as in aquaculture, is essential. Thus, in this study, we tested the efficacy of selected cyanocides towards bloom control in laboratory and outdoor mesocosm experiments. Specifically, we focused on the applicability of a group of cationic disinfectants, alkyltrimethyl ammonium (ATMA) compounds and H₂O₂. The biocidal effect of four ATMA cations with different alkyl chain lengths was evaluated ex situ using Microcystis colonies collected from a fish pond. The most effective compound, octadecyl trimethyl ammonium (ODTMA), was further evaluated for its selectivity towards 24 cyanobacteria and eukaryotic algae species, including Cyanobacteria, Chlorophyta, Bacillariophyta, Euglenozoa and Cryptophyta. The results indicated selective inhibition of cyanobacteria by ODTMA-Br (C18) on both Chroccocales and Nostocales, but a minor effect on Chlorophytes and Bacillariophytes. The efficacy of ODTMA-Br (C18) (6.4 μM) in mitigating the Microcystis population was compared with that of a single low dose of H₂O₂ treatments (117.6 μM). ODTMA-Br (C18) suppressed the regrowth of Microcystis for a longer duration than did H₂O₂. The results suggested that ODTMA-Br (C18) may be used as an effective cyanocide and that it is worth further evaluating this group of cationic compounds as a treatment to mitigate cyanobacterial blooms in aquaculture.

Grazer-Induced Chemical Defense in a Microcystin-Producing Microcystis aeruginosa (Cyanobacteria) Exposed to Daphnia gessneri Infochemicals

Cyanobacteria are photosynthetic microorganisms that compose phytoplankton and therefore have a trophic relationship with zooplankton, which represent an important link for energy flux in aquatic food webs. Several species can form blooms and produce bioactive metabolites known as cyanotoxins. However, the ecological and adaptative role of these toxins are still under debate. Many studies have addressed the cyanotoxins' function in defense against herbivory when grazing pressure by zooplankton plays a role in phytoplankton top-down control. Thus, the present study evaluated the ecophysiological responses of the cyanobacterial strain Microcystis aeruginosa NPLJ-4 underlying the chemical induced defense against the cladoceran Daphnia gessneri. Exposure to predator infochemicals consisted of cultures established in ASM-1 medium prepared in a filtrate from a culture of adults of D. gessneri at an environmentally relevant density. Daphnia infochemicals promoted a significant increase in toxin production by M. aeruginosa. However, no differences in growth were observed, despite a significant increase in both maximum photosynthetic efficiency and electron transport rate in response to zooplankton. Additionally, there was no significant variation in the production of exopolysaccharides. Overall, although a grazer-induced defense response was demonstrated, there were no effects on M. aeruginosa fitness, which maintained its growth in the presence of Daphnia alarm cues.

CyanoMetDB, a comprehensive public database of secondary metabolites from cyanobacteria

Harmful cyanobacterial blooms, which frequently contain toxic secondary metabolites, are reported in aquatic environments around the world. More than two thousand cyanobacterial secondary metabolites have been reported from diverse sources over the past fifty years. A comprehensive, publically-accessible database detailing these secondary metabolites would facilitate research into their occurrence, functions and toxicological risks. To address this need we created CyanoMetDB, a highly curated, flat-file, openly-accessible database of cyanobacterial secondary metabolites collated from 850 peer-reviewed articles published between 1967 and 2020. CyanoMetDB contains 2010 cyanobacterial metabolites and 99 structurally related compounds. This has nearly doubled the number of entries with complete literature metadata and structural composition information compared to previously available open access databases. The dataset includes microcytsins, cyanopeptolins, other depsipeptides, anabaenopeptins, microginins, aeruginosins, cyclamides, cryptophycins, saxitoxins, spumigins, microviridins, and anatoxins among other metabolite classes. A comprehensive database dedicated to cyanobacterial secondary metabolites facilitates: (1) the detection and dereplication of known cyanobacterial toxins and secondary metabolites; (2) the identification of novel natural products from cyanobacteria; (3) research on biosynthesis of cyanobacterial secondary metabolites, including substructure searches; and (4) the investigation of their abundance, persistence, and toxicity in natural environments.

Cyanobacterial anabaenopeptin-B, microcystins and their mixture cause toxic effects on the behavior of the freshwater crustacean Daphnia magna (Cladocera)

Comparison of the toxic effects caused by the pure cyanobacterial cyclic hexapeptide anabaenopeptin-B (AN-B), the heptapeptides: microcystin-LR (MC-LR) and MC-LF as well as a binary mixture of AN-B with MC-LR on the swimming speed and hopping frequency - essential activities of Daphnia, was experimentally determined. Till now, no information on behavioral effects of AN-B and its mixture with microcystins, commonly produced by cyanobacteria, was available. Also MC-LF effect on aquatic crustaceans was determined for the first time. The results showed that AN-B exerted considerable inhibition of D. magna swimming speed and hopping frequency similar to MC-LR and MC-LF. The mixture of AN-B and MC-LR caused stronger toxic effects, than the individual oligopeptides used at the same concentration. The much lower 48 h- EC₅₀ value of the AN-B and MC-LR mixture (0.95 ± 0.12 μg/mL) than those of individual oligopeptides AN-B (6.3 ± 0.63 μg/mL), MC-LR (4.0 ± 0.27 μg/mL), MC-LF (3.9 ± 0.20 μg/mL) that caused swimming speed inhibition explains the commonly observed stronger toxicity of complex crude cyanobacterial extracts to daphnids than individual microcystins. The obtained results indicated that AN-B, microcystins and their mixture exerted time- and concentration-dependent motility disturbances of crustaceans and they can be good candidates for evaluation of toxicity in early warning systems. Other cyanobacterial oligopeptides beyond microcystins should be considered as a real threat for aquatic organisms.

Multibiomarker-based assessment of toxicity of central European strains of filamentous cyanobacteria Aphanizomenon gracile and Raphidiopsis raciborskii to zebrafish Danio rerio

The global increase in cyanobacterial blooms poses environmental and health threats. Selected cyanobacterial strains reveal toxicities despite a lack of synthesis of known toxic metabolites, and the mechanisms of these toxicities are not well understood. Here we investigated the toxicity of non-cylindrospermopsin and non-microcystin producing Aphanizomenon gracile and Raphidiopsis raciborskii of Central European origin to zebrafish exposed for 14 days to their extracts. Toxicological screening revealed the presence of anabaenopeptins and a lack of anatoxin-a, ß-methylamino-L-alanine or saxitoxins in examined extracts. The responses were compared to 20 μg L^-1 of common cyanobacterial toxins cylindrospermopsin (CYN) and microcystin-LR (MC-LR). The expression of the marker genes involved in apoptosis (caspase 3a and 3b, Bcl-2, BAX, p53, MAPK, Nrf2), DNA damage detection and repair (GADD45, RAD51, JUN, XPC), detoxification (CYP1A, CYP26, EPHX1), lipid metabolism (PPARa, FABP1, PLA2), phosphorylation/dephosphorylation (PPP6C, PPM1) and cytoskeleton (actin, tubulin) were examined using targeted transcriptomics. Cellular stress and toxicity biomarkers (oxidative injury, antioxidant enzymes, thiol pool status, and lactate dehydrogenase activity) were measured in the liver, and acetylcholinesterase activity was determined as an index of neurotoxicity in the brain. The extracts of three cyanobacterial strains that produce no known cyanotoxins caused marked toxicity in D. rerio, and the biomarker profiles indicate different toxic mechanisms between the bioactive compounds extracted from these strains and the purified cyanotoxins. All studied cyanobacterial extracts and purified cyanotoxins induced oxidative stress and neurotoxicity, downregulated Nrf2 and CYP26B1, disrupted phosphorylation/dephosphorylation processes and actin/tubulin cytoskeleton and upregulated apoptotic activity in the liver. The tested strains and purified toxins displayed distinctively different effects on lipid metabolism. Unlike CYN and MC-LR, the Central European strain of A. gracile and R. raciborskii did not reveal a genotoxic potential. These findings help to further understand the ecotoxicological consequences of toxic cyanobacterial blooms in freshwater ecosystems.

Diagnostic Fragmentation Filtering for Cyanopeptolin Detection

Cyanobacteria are ubiquitous photosynthetic prokaryotes that produce structurally diverse bioactive metabolites. Although microcystins are extensively studied, other cyanopeptides produced by common bloom-forming species have received little attention. Cyanopeptolins are a large cyanopeptide group that contain a characteristic 3-amino-6-hydroxy-2-piperidone (Ahp) moiety. In the present study we used diagnostic fragmentation filtering (DFF), a semitargeted liquid chromatography-tandem mass spectrometry (MS/MS) product ion filtering approach, to investigate cyanopeptolin diversity from 5 Microcystis strains and 4 bloom samples collected from lakes in Ontario and Quebec, Canada. Data processing by DFF was used to search MS/MS data sets for pairs of diagnostic product ions corresponding to cyanopeptolin partial sequences. For example, diagnostic product ions at m/z 150.0912 and 215.1183 identified cyanopeptolins with the NMe-Tyr-Phe-Ahp partial sequence. Forty-eight different cyanopeptolins, including 35 new variants, were detected from studied strains and bloom samples. Different cyanopeptolin profiles were identified from each sample. We detected a new compound, cyanopeptolin 1143, from a bloom and elucidated its planar structure from subsequent targeted MS/MS experiments. Diagnostic fragmentation filtering is a rapid, easy-to-perform postacquisition metabolomics strategy for inferring structural features and prioritizing new compounds for further study and dereplication. More work on cyanopeptolin occurrence and toxicity is needed because their concentrations in freshwater lakes after blooms can be similar to those of microcystins. Environ Toxicol Chem 2021;40:1087-1097. © 2020 SETAC.

Antibiotic pollution promotes dominance by harmful cyanobacteria: A case study examining norfloxacin exposure in competition experiments

Cyanobacterial harmful algal blooms (cyanoHABs) in freshwater lakes across the globe are often combined with other stressors. Pharmaceutical pollution, especially antibiotics in water bodies, poses a potential hazard in aquatic ecosystems. However, how antibiotics influence the risk of cyanoHABs remains unclear. Here, we investigated the effects of norfloxacin (NOR), one of the most widely used antibiotics globally, to a bloom-forming cyanobacterium (Microcystis aeruginosa) and a common green alga (Scenedesmus quadricauda), under both mono- and coculture conditions. Taxon-specific responses to NOR were evaluated in monoculture. In addition, the growth rate and change in ratio of cyanobacteria to green algae when cocultured with exposure to NOR were determined. In monocultures of Microcystis, exposure to low concentrations of NOR resulted in decreases in biomass, chlorophyll a and soluble protein content, while superoxide anion content and superoxide dismutase activity increased. However, NOR at high concentration only slightly affected Scenedesmus. During the co-culture trials of Microcystis and Scenedesmus, the 5 μg · L^-1 NOR treatment increased the ratio of Microcystis to co-cultured Scenedesmus by 47.2%. Meanwhile, although Scenedesmus growth was enhanced by 4.2% under NOR treatment in monoculture, it was conversely inhibited by 63.4% and 38.2% when co-cultured with Microcystis with and without NOR, respectively. Our results indicate that antibiotic pollution has a potential risk to enhance the perniciousness of cyanoHABs by disturbing interspecific interaction between cyanobacteria and green algae. These results reinforce the need for scientists and managers to consider the influence of xenobiotics in shaping the outcome of interactions among multiple species in aquatic ecosystems.

Anatoxin-a: Overview on a harmful cyanobacterial neurotoxin from the environmental scale to the molecular target

Anatoxin-a (ATX-a) is a neurotoxic alkaloid, produced by several freshwater planktonic and benthic cyanobacteria (CB). Such CB have posed human and animal health issues for several years, as this toxin is able to cause neurologic symptoms in humans following food poisoning and death in wild and domestic animals. Different episodes of animal intoxication have incriminated ATX-a worldwide, as confirmed by the presence of ATX-a-producing CB in the consumed water or biofilm, or the observation of neurotoxic symptoms, which match experimental toxicity in vivo. Regarding toxicity parameters, toxicokinetics knowledge is currently incomplete and needs to be improved. The toxin can passively cross biological membranes and act rapidly on nicotinic receptors, its main molecular target. In vivo and in vitro acute effects of ATX-a have been studied and make possible to draw its mode of action, highlighting its deleterious effects on the nervous systems and its effectors, namely muscles, heart and vessels, and the respiratory apparatus. However, very little is known about its putative chronic toxicity. This review updates available data on ATX-a, from the ecodynamic of the toxin to its physiological and molecular targets.

Total Synthesis of the Proposed Microcyclamides MZ602 and MZ568

The first convergent total synthesis for the proposed structures of microcyclamides MZ602 (1) and MZ568 (2) has been accomplished in 11 linear steps with 12.5 and 16.8% overall yield, respectively. Key features of the syntheses include a one-pot cascade reaction to construct core Boc-l-Ile-Thz-OAllyl fragment 5, and a removable pseudoproline (Ψ^Me,Me pro) inducer assisted cyclization of thiazole-containing all-l linear peptides. The spectral data (¹H NMR, ¹³C NMR, and HRMS) of synthetic MZ602 (1) were quite similar to those of the proposed natural microcyclamide MZ602, except to an opposite sign of the optical rotation value. Surprisingly, the synthetic MZ568 (2) presented large discrepancies in characteristic spectral data from those of the reported natural product, although the absolute configuration of key intermediate 36 was unambiguously determined by single-crystal X-ray analysis in our work. These findings revealed that the proposed structures of natural microcyclamides MZ602 and MZ568 required revision.

Genomic screening and molecular dynamics simulations of cyanovirin-N homologs from cyanobacteria phylum

The phylum cyanobacteria are one of the most ancient groups of organisms on the planet and are well recognized due to its wide distribution, ecological role, and biotechnological potential. Cyanobacterial lectins are being extensively explored due to their antiviral activity, mainly because of their capacity of inhibiting HIV strains from infecting human cells by gp120 and gp41 binding. Cianovirin-N from Nostoc ellipsosporum was the first lectin isolated with this property. Since then, various homologs have been discovered and characterized. In this article, we present results of a genomic screening to find cyanovirin-N homologs (CVNH) in all cyanobacteria genomes available in the GenBank, resulting in 155 CVNH proteins with 63 presenting significant identity differences of cyanovirin-N. Homology modeling and molecular dynamics were employed to characterize 18 unexplored models and their functional capacity of binding to Manα(1-2)Man. Results presented here support the hypothesis of multiple ligand recognition for the CVNH family and may help to understand the function of these lectins for the producer cyanobacteria. Additionally, the theoretical results observed here justify carrying out experimental investigations that can expand the therapeutic potential of cyanobacterial lectins.

Preliminary Assessment of Microbial Community Structure of Wind-Tidal Flats in the Laguna Madre, Texas, USA

Aside from two samples collected nearly 50 years ago, little is known about the microbial composition of wind tidal flats in the hypersaline Laguna Madre, Texas. These mats account for ~42% of the lagoon's area. These microbial communities were sampled at four locations that historically had mats in the Laguna Madre, including Laguna Madre Field Station (LMFS), Nighthawk Bay (NH), and two locations in Kenedy Ranch (KRN and KRS). Amplicon sequencing of 16S genes determined the presence of 51 prokaryotic phyla dominated by Bacteroidota, Chloroflexi, Cyanobacteria, Desulfobacteria, Firmicutes, Halobacteria, and Proteobacteria. The microbial community structure of NH and KR is significantly different to LMFS, in which Bacteroidota and Proteobacteria were most abundant. Twenty-three cyanobacterial taxa were identified via genomic analysis, whereas 45 cyanobacterial taxa were identified using morphological analysis, containing large filamentous forms on the surface, and smaller, motile filamentous and coccoid forms in subsurface mat layers. Sample sites were dominated by species in Oscillatoriaceae (i.e., Lyngbya) and Coleofasciculaceae (i.e., Coleofasciculus). Most cyanobacterial sequences (~35%) could not be assigned to any established taxa at the family/genus level, given the limited knowledge of hypersaline cyanobacteria. A total of 73 cyanobacterial bioactive metabolites were identified using ultra performance liquid chromatography-Orbitrap MS analysis from these commu nities. Laguna Madre seems unique compared to other sabkhas in terms of its microbiology.

A genomic view of trophic and metabolic diversity in clade-specific Lamellodysidea sponge microbiomes

BACKGROUND

Marine sponges and their microbiomes contribute significantly to carbon and nutrient cycling in global reefs, processing and remineralizing dissolved and particulate organic matter. Lamellodysidea herbacea sponges obtain additional energy from abundant photosynthetic Hormoscilla cyanobacterial symbionts, which also produce polybrominated diphenyl ethers (PBDEs) chemically similar to anthropogenic pollutants of environmental concern. Potential contributions of non-Hormoscilla bacteria to Lamellodysidea microbiome metabolism and the synthesis and degradation of additional secondary metabolites are currently unknown.

RESULTS

This study has determined relative abundance, taxonomic novelty, metabolic capacities, and secondary metabolite potential in 21 previously uncharacterized, uncultured Lamellodysidea-associated microbial populations by reconstructing near-complete metagenome-assembled genomes (MAGs) to complement 16S rRNA gene amplicon studies. Microbial community compositions aligned with sponge host subgroup phylogeny in 16 samples from four host clades collected from multiple sites in Guam over a 3-year period, including representatives of Alphaproteobacteria, Gammaproteobacteria, Oligoflexia, and Bacteroidetes as well as Cyanobacteria (Hormoscilla). Unexpectedly, microbiomes from one host clade also included Cyanobacteria from the prolific secondary metabolite-producer genus Prochloron, a common tunicate symbiont. Two novel Alphaproteobacteria MAGs encoded pathways diagnostic for methylotrophic metabolism as well as type III secretion systems, and have been provisionally assigned to a new order, designated Candidatus Methylospongiales. MAGs from other taxonomic groups encoded light-driven energy production pathways using not only chlorophyll, but also bacteriochlorophyll and proteorhodopsin. Diverse heterotrophic capabilities favoring aerobic versus anaerobic conditions included pathways for degrading chitin, eukaryotic extracellular matrix polymers, phosphonates, dimethylsulfoniopropionate, trimethylamine, and benzoate. Genetic evidence identified an aerobic catabolic pathway for halogenated aromatics that may enable endogenous PBDEs to be used as a carbon and energy source.

CONCLUSIONS

The reconstruction of high-quality MAGs from all microbial taxa comprising greater than 0.1% of the sponge microbiome enabled species-specific assignment of unique metabolic features that could not have been predicted from taxonomic data alone. This information will promote more representative models of marine invertebrate microbiome contributions to host bioenergetics, the identification of potential new sponge parasites and pathogens based on conserved metabolic and physiological markers, and a better understanding of biosynthetic and degradative pathways for secondary metabolites and halogenated compounds in sponge-associated microbiota. Video Abstract.

The Occurrence of Potential Harmful Cyanobacteria and Cyanotoxins in the Obrzyca River (Poland), a Source of Drinking Water

Harmful cyanobacteria and their cyanotoxins may contaminate drinking water resources and their effective control remains challenging. The present study reports on cyanobacterial blooms and associated cyanotoxins in the Obrzyca River, a source of drinking water in Poland. The river was examined from July to October 2019 and concentrations of microcystins, anatoxin-a, and cylindrospermopsin were monitored. The toxicity of water samples was also tested using an ecotoxicological assay. All studied cyanotoxins were detected with microcystins revealing the highest levels. Maximal microcystin concentrations (3.97 μg/L) were determined in September at Uście point, exceeding the provisional guideline. Extracts from Uście point, where the dominant species were Dolichospermum flos-aquae (August), Microcystis aeruginosa (September), and Planktothrix agardhii (October), were toxic for Dugesia tigrina Girard. Microcystin concentrations (MC-LR and MC-RR) were positively correlated with cyanobacteria biovolume. Analysis of the chemical indicators of water quality has shown relationships between them and microcystins as well as cyanobacteria abundance.

New insights into the harmful algae inhibition by Spartina alterniflora: Cellular physiology and metabolism of extracellular secretion

This study investigated the response of three toxic harmful algal blooms (HABs) species, Heterosigma akashiwo, Chattonella marina, and Alexandrium tamarense to coastal invasive plant, Spartina alterniflora. In this study, the growth of three HABs species were suppressed significantly by S. alterniflora extracts, showing a dose-response relationship. The raphidophyte H. akashiwo and C. marina exhibited higher inhibitory response with EC_50,7d decreased by 14% and 75% as compared to the dinoflagellate A. tamarense. C. marina was the most sensitive among the three species. S. alterniflora extracts disrupted algal cellular integrity and photosynthesis. Furthermore, the extracellular organic matters were detected by fluorescence excitation-emission matrix. Algal metabolites, protein-like substances (tyrosine-like peak and tryptophan-like peak) decreased as time prolonged and the humic-like substances (UVA marine humic-like peak) increased when algal cells were exposed to S. alterniflora extracts. These results provide new insights to the inhibition mechanism of S. alterniflora extracts on HABs species.

Saxitoxin-producing Raphidiopsis raciborskii (cyanobacteria) inhibits swimming and physiological parameters in Daphnia similis

In this study we tested the effects of a neurotoxic strain of the cyanobacterium Raphidiopsis raciborskii (CYRF-01) on the swimming activity and physiological parameters of Daphnia similis such as movements of the antennae, thoracic limbs, post-abdominal claw and heart rate. An acute assay was performed to test the effect on swimming activity, exposing newborns (<24 h) to different concentrations of live cells and observing the number of immobilized animals over a period of 48 h. For testing the effects on physiological parameters adult females (10-15 days) were exposed in a flow-through system and recorded with a digital camera. Results showed rapid effect of the strain CYRF on all parameters. Animals started to be immobilized in the first 30 min exposure and showed complete paralysis after 2 h in 500 μg L^-1 and after 24 h in the other concentrations. Physiological parameters accompanied the same response pattern with effects starting after 30 min and some recovery at the end of 6 h exposure. Antennae stopped moving after 2-3 h at 250-500 μg L^-1, explaining the paralysis of the swimming activity in Daphnia. Thoracic limbs movements were significantly inhibited after 30 min in all concentrations, staying at lower levels than control through the experiment. Post-abdominal claw movement were completely ceased after 30 min and remained stopped until the end of the trial. Heart rate showed a tendency to decrease abruptly in the first 30 min exposure in all concentrations, but showed significant lower values than control only at 500 μg L^-1, between 3 and 4 h exposure, and a recovery at the end of 6 h. In conclusion, results show that neurotoxic cyanobacteria can impose severe constrains on the physiology of daphniids, which can have consequences to the oxygen uptake, swimming and feeding behavior and to the overall fitness of those organisms.

Biochemical parameters in skin and muscle of Pelophylax kl. esculentus frogs: Influence of a cyanobacterial bloom in situ

There is little information in scientific literature as to how conditions created by a microcystin (MC) producing cyanobacterial bloom affect the oxidant/antioxidant, biotransformation and neurotoxicity parameters in adult frogs in situ. We investigated biochemical parameters in the skin and muscle of Pelophylax kl. esculentus from Lake Ludaš (Serbia) by comparing frogs that live on the northern bloom side (BS) of the lake with those that inhabit the southern no-bloom side (NBS). A higher protein carbonylation level and lower antioxidant defense system capability in the skin of frogs living in conditions of the cyanobacterial bloom were observed. Inhibition of glutathione-dependent machinery was the major mechanism responsible for the induction of cyanobacterial bloom-mediated oxidative stress in frog skin. On the other hand, the detected higher ability of muscle to overcome bloom prooxidant toxicity was linked to a higher efficiency of the biotransformation system through glutathione-S-transferase activity and/or was the consequence of indirect exposure of the tissue to the bloom. Our results have also revealed that the cyanobacterial bloom conditions induced the cholinergic neurotransmitter system in both tissues. This study provides a better understanding of the ecotoxicological impact of the MC producing cyanobacterial bloom on frogs in situ. However, further investigations of the complex mechanism involved in cyanobacterial bloom toxicity in real environmental conditions are required.

A Convolutional Neural Network-Based Approach for the Rapid Annotation of Molecularly Diverse Natural Products

This report describes the first application of the novel NMR-based machine learning tool "Small Molecule Accurate Recognition Technology" (SMART 2.0) for mixture analysis and subsequent accelerated discovery and characterization of new natural products. The concept was applied to the extract of a filamentous marine cyanobacterium known to be a prolific producer of cytotoxic natural products. This environmental Symploca extract was roughly fractionated, and then prioritized and guided by cancer cell cytotoxicity, NMR-based SMART 2.0, and MS²-based molecular networking. This led to the isolation and rapid identification of a new chimeric swinholide-like macrolide, symplocolide A, as well as the annotation of swinholide A, samholides A-I, and several new derivatives. The planar structure of symplocolide A was confirmed to be a structural hybrid between swinholide A and luminaolide B by 1D/2D NMR and LC-MS² analysis. A second example applies SMART 2.0 to the characterization of structurally novel cyclic peptides, and compares this approach to the recently appearing "atomic sort" method. This study exemplifies the revolutionary potential of combined traditional and deep learning-assisted analytical approaches to overcome longstanding challenges in natural products drug discovery.