Diversity, Cyanotoxin Production, and Bioactivities of Cyanobacteria Isolated from Freshwaters of Greece

Comprehensive analysis of cyanobacterial secondary metabolites distribution and toxicity in urban water bodies

This study addresses the increasing concern regarding cyanotoxin contamination of water bodies, highlighting the diversity of these toxins and their potential health implications. Cyanobacteria, which are prevalent in aquatic environments, produce toxic metabolites, raising concerns regarding human exposure and associated health risks, including a potential increase in cancer risk. Although existing research has primarily focused on well-known cyanotoxins, recent technological advancements have revealed numerous unknown cyanotoxins, necessitating a comprehensive assessment of multiple toxin categories. To enhance the cyanotoxin databases, we optimized the CyanoMetDB cyanobacterial secondary metabolites database by incorporating secondary fragmentation patterns using the Mass Frontier fragmentation data prediction software. Water samples from diverse locations in Shanghai were analyzed using high-resolution mass spectrometry. Subsequently, the toxicity of cyanobacterial metabolites in the water samples was examined through acute toxicity assays using the crustacean Thamnocephalus platyurus. After 24 h of exposure, the semi-lethal concentrations (LC50) of the water samples ranged from 0.31 mg L-1 to 1.78 mg L-1 (MC-LR equivalent concentration). Our findings revealed a critical correlation between the overall concentration of cyanobacterial metabolites and toxicity. The robust framework and insights of this study underscore the need for an inclusive approach to water quality management, emphasizing continuous efforts to refine detection methods and comprehend the broader ecological impact of cyanobacterial blooms on aquatic ecosystems.

Effect of Nitrogen, Salinity, and Light Intensity on the Biomass Composition of Nephroselmis sp.: Optimization of Lipids Accumulation (Including EPA)

Microalgal biomass is characterized by high protein, carbohydrates, and lipids concentrations. However, their qualitative and quantitative compositions depend not only on the cultivated species but also on the cultivation conditions. Focusing on the microalgae's ability to accumulate significant fatty acids (FAs) amounts, they can be valorized either as dietary supplements or for biofuel production, depending on the accumulated biomolecules. In this study, a local isolate (Nephroselmis sp.) was precultured under autotrophic conditions, while the Box-Behnken experimental design followed using the parameters of nitrogen (0-250 mg/L), salinity (30-70 ppt) and illuminance (40-260 μmol m^-2 s^-1) to evaluate the accumulated biomolecules, with an emphasis on the amount of FAs and its profile. Regardless of the cultivation conditions, the FAs of C14:0, C16:0, and C18:0 were found in all samples (up to 8% w/w in total), while the unsaturated C16:1 and C18:1 were also characterized by their high accumulations. Additionally, the polyunsaturated FAs, including the valuable C20:5n3 (EPA), had accumulated when the nitrogen concentration was sufficient, and the salinity levels remained low (30 ppt). Specifically, EPA approached 30% of the total FAs. Therefore, Nephroselmis sp. could be considered as an alternative EPA source compared to the already-known species used in food supplementation.

Biotests in Cyanobacterial Toxicity Assessment-Efficient Enough or Not?

Cyanobacteria are a diverse group of organisms known for producing highly potent cyanotoxins that pose a threat to human, animal, and environmental health. These toxins have varying chemical structures and toxicity mechanisms and several toxin classes can be present simultaneously, making it difficult to assess their toxic effects using physico-chemical methods, even when the producing organism and its abundance are identified. To address these challenges, alternative organisms among aquatic vertebrates and invertebrates are being explored as more assays evolve and diverge from the initially established and routinely used mouse bioassay. However, detecting cyanotoxins in complex environmental samples and characterizing their toxic modes of action remain major challenges. This review provides a systematic overview of the use of some of these alternative models and their responses to harmful cyanobacterial metabolites. It also assesses the general usefulness, sensitivity, and efficiency of these models in investigating the mechanisms of cyanotoxicity expressed at different levels of biological organization. From the reported findings, it is clear that cyanotoxin testing requires a multi-level approach. While studying changes at the whole-organism level is essential, as the complexities of whole organisms are still beyond the reach of in vitro methodologies, understanding cyanotoxicity at the molecular and biochemical levels is necessary for meaningful toxicity evaluations. Further research is needed to refine and optimize bioassays for cyanotoxicity testing, which includes developing standardized protocols and identifying novel model organisms for improved understanding of the mechanisms with fewer ethical concerns. In vitro models and computational modeling can complement vertebrate bioassays and reduce animal use, leading to better risk assessment and characterization of cyanotoxins.

Microcystin-LR and cyanobacterial extracts alter the distribution of cell wall matrix components in rice root cells

Cyanobacterial toxins (known as cyanotoxins) disrupt the plant cytoskeleton (i.e. microtubules and F-actin), which is implicated in the regulation of cell wall architecture. Therefore, cyanotoxins are also expected to affect cell wall structure and composition. However, the effects of cyanobacterial toxicity on plant cell wall have not been yet thoroughly studied. Accordingly, the alterations of cell wall matrix after treatments with pure microcystin-LR (MC-LR), or cell extracts of one MC-producing and one non-MC-producing Microcystis strain were studied in differentiated Oryza sativa (rice) root cells. Semi-thin transverse sections of variously treated LR-White-embedded roots underwent immunostaining for various cell wall epitopes, including homogalacturonans (HGs), arabinogalactan-proteins (AGPs), and hemicelluloses. Homogalacturonan and arabinan distribution patterns were altered in the affected roots, while a pectin methylesterase (PME) activity assay revealed that PMEs were also affected. Elevated intracellular Ca²⁺ levels, along with increased callose and mixed linkage glucans (MLGs) deposition, were also observed after treatment. Xyloglucans appeared unaffected and lignification was not observed. The exact mechanism of cyanobacterial toxicity against the cell wall is to be further investigated.

Current research scenario for biological effect of exogenous factors on microcystin synthesis

In natural water bodies, numerous cyanobacteria have the potential to intracellularly synthesize cyanotoxins, among which microcystin (MC) is the ubiquitous toxin that has been well known to be carcinogenic for hepatocytes. MC synthesis is a complex process, which involves about 10 non-ribosomal proteins encoded by the mcy gene cluster. In the natural environments containing MC-producing cyanobacteria, a variety of external factors can affect the generation of MC by mediating the expression of synthesizing genes. These factors can be generally divided into biotic factors (e.g., daphnia, virioplankton, MC-degrading bacteria, algicidal bacteria) and abiotic factors (e.g., nutrients, physical factors, chemicals, phytochemicals, essential trace elements), which are of great significance to the effective reduction of MC. Furthermore, comparison of MC-synthesizing genes in different cyanobacterial strains was performed, and the related factors affecting MC synthesis were summarized. Then, the problems and gaps regarding the biological effect of exogenous factors on microcystin synthesis were discussed. This review article may provide new ideas for addressing the challenges and bottlenecks of MC management.

Cyanobacteria in hot pursuit: Characterization of cyanobacteria strains, including novel taxa, isolated from geothermal habitats from different ecoregions of the world

Well-studied thermal spring microbial mat systems continue to serve as excellent models from which to make discoveries of general importance to microbial community ecology in order to address comprehensively the question of "who is there" in a microbial community. Cyanobacteria are highly adaptable and an integral part of many ecosystems including thermal springs. In this context, we sampled disparate thermal springs, spanning from Iceland and Poland to Greece and Tajikistan. Thirteen (13) strains were isolated and characterised with taxonomic indices and molecular markers (16S-23S rRNA region and cpcBA gene), whilst their thermotolerance was evaluated. Screening for the presence of genes encoding three heat shock proteins, as well as non-ribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs) was performed. This approach resulted in the description of two new genera (Hillbrichtia and Amphirytos) and their type species (Hillbrichtia pamiria and Amphirytos necridicus) representing Oscillatoriales and Synechococcales orders, respectively. We also found unique lineages inside the genus Thermoleptolyngbya, describing a novel species (T. hindakiae). We described the presence of sub-cosmopolitan taxa (such as Calothrix, Desertifilum, and Trichormus). Strains were diverse concerning their thermophilic ability with the strains well adapted to high temperatures possessing all three investigated genes encoding heat shock proteins as well as studied PKS and NRPS genes. In this work, we show novel cyanobacteria diversity from thermal springs from disparate environments, possible correlation of thermotolerance and their genetic background, which may have implications on strategic focusing of screening programs on underexploited taxa in these habitats.

In vivo and in silico screening for antimicrobial compounds from cyanobacteria

Due to the emerging rise of multi‐drug resistant bacteria, the discovery of novel antibiotics is of high scientific interest. Through their high chemodiversity of bioactive secondary metabolites, cyanobacteria have proven to be promising microorganisms for the discovery of antibacterial compounds. These aspects make appropriate antibacterial screening approaches for cyanobacteria crucial. Up to date, screenings are mostly carried out using a phenotypic methodology, consisting of cyanobacterial cultivation, extraction, and inhibitory assays. However, the parameters of these methods highly vary within the literature. Therefore, the common choices of parameters and inhibitory assays are summarized in this review. Nevertheless, less frequently used method variants are highlighted, which lead to hits from antimicrobial compounds. In addition to the considerations of phenotypic methods, this study provides an overview of developments in the genome‐based screening area, be it in vivo using PCR technique or in silico using the recent genome‐mining method. Though, up to date, these techniques are not applied as much as phenotypic screening.

Anabaenopeptins from Cyanobacteria in Freshwater Bodies of Greece

Cyanobacteria are photosynthetic microorganisms that are able to produce a large number of secondary metabolites. In freshwaters, under favorable conditions, they can rapidly multiply, forming blooms, and can release their toxic/bioactive metabolites in water. Among them, anabaenopeptins (APs) are a less studied class of cyclic bioactive cyanopeptides. The occurrence and structural variety of APs in cyanobacterial blooms and cultured strains from Greek freshwaters were investigated. Cyanobacterial extracts were analyzed with LC-qTRAP MS/MS using information-dependent acquisition in enhanced ion product mode in order to obtain the fragmentation mass spectra of APs. Thirteen APs were detected, and their possible structures were annotated based on the elucidation of fragmentation spectra, including three novel ones. APs were present in the majority of bloom samples (91%) collected from nine Greek lakes during different time periods. A large variety of APs was observed, with up to eight congeners co-occurring in the same sample. AP F (87%), Oscillamide Y (87%) and AP B (65%) were the most frequently detected congeners. Thirty cyanobacterial strain cultures were also analyzed. APs were only detected in one strain (Microcystis ichtyoblabe). The results contribute to a better understanding of APs produced by freshwater cyanobacteria and expand the range of structurally characterized APs.

Unravelling unknown cyanobacteria diversity linked with HCN production

Cyanobacteria are ecologically versatile microorganisms, occupying diverse habitats, from terrestrial caves to coastal shores and from brackish lakes to thermal springs. Cyanobacteria have also been linked with hydrogen cyanide (HCN), mainly for their ability to catabolize HCN by the nitrogenase enzyme. In this context, we sampled disparate environments, spanning from Canary Islands and Iceland to Estonia and Cyprus. Eighty-one (81) strains were isolated and characterised with taxonomic indices and molecular markers (16S-23S rRNA region and cpcBA region), whilst their ability to produce HCN was evaluated. This approach resulted in the description of five new genera (Speleotes, Haliplanktos, Olisthonema, Speos, and Iphianassa) and their type species (S. anchialus, H. antonyquinny, O. eestii, S. fyssassi, I. zackieohae) representing Chroococcales, Chroococcidiopsales, Oscillatoriales, Synechococcales, and Nostocales orders, respectively. We also found unique lineages inside the genera Komarekiella, Stenomitos, Cyanocohniella, and Nodularia, describing four new species (K. chia, S. pantisii, C. hyphalmyra, N. mediterannea). We report for the first time a widespread production of HCN amongst different taxa and habitats. Epilithic lifestyle, where cyanobacteria are more vulnerable to grazers, had the largest relative frequency in HCN production. In this work, we show novel cyanobacteria diversity from various habitats, including an unexplored anchialine cave, and possible correlation of cyanobacteria chemo- with species diversity, which may have implications on strategic focusing of screening programs on underexploited taxa and/or habitats.

Phototransformation of an emerging cyanotoxin (Aerucyclamide A) in simulated natural waters

Aerucyclamide A (ACA) is an emerging cyanopeptide toxin produced by cyanobacteria, and its transformation pathway has rarely been reported. In the present study, ACA was purified from cyanobacterial extracts, and photodegradation processes were investigated in dissolved organic matter (DOM) solutions. Under simulated solar irradiation, the photodegradation of ACA was dominated by ^•OH oxidation, accounting for ~72% of the indirect photodegradation. The bimolecular reaction rate constant of ACA with ^•OH was (6.4 ± 0.2) × 10⁹M ^- 1s ^- 1. Our results indicated that the major reactive sites of ACA toward ^•OH are thiazoline and thiazole moieties. Product analysis via high-resolution mass spectrometry suggested that hydrogen abstraction and gradual hydroxylation are the main photodegradation pathways. The acute toxicity assessment indicate that the products generated in photolysis process did not show any measurable toxicity to Thamnocephalus platyurus. Photodegradation experiments with various DOM-phycocyanin mixtures demonstrated that the half-life of ACA is much longer than that of microcystin-LR.

Biodiversity, phylogeny and toxin production profile of cyanobacterial strains isolated from lake Latyan in Iran

Monitoring toxigenic cyanobacteria in freshwaters is of great importance due to the adverse health impacts on humans and aquatic organisms. Here we studied cyanobacterial occurrence and biodiversity in a drinking water reservoir in Tehran province, Iran. In total, nine different species representing three orders of Synechococcales, Oscillatoriales and Nostocales were isolated and classified into six families and seven genera ranging from 92.3% to 99.0% similarities in their partial 16S rDNA with GenBank sequences. The cultures were analyzed for cyanotoxins production by the Artemia salina bioassay, ultrahigh performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and also screened for the presence of marker genes involved in toxins production. Ethyl acetate extracts of three strains showed more than 50% mortality on A. salina larvae after 24 h at a concentration of 500 µg/ml. Production of at least one of the cyanotoxins, microcystin (MC), cylindrospermopsin (CYN) and anatoxin-a (ATX-a), was detected in 6 of the strains. Seven MC variants with a total concentration of 130.6 ng/mg of biomass dry weight were detected for the strain Phormidium sp. UTMC6001 and molecular screening of the mcyE gene also confirmed the presence of this biomarker in its genome. Our study also revealed the production of CYN in a novel picocyanobacterial strain Cyanobium sp. UTMC6007 at 1.0 ng/mg of biomass dry weight. Considering the limited information on freshwater toxic cyanobacteria taxonomy in the Middle East, these findings will expand our knowledge and consequently aid in development of new water management policies in future.

Connectivity of Edaphic and Endolithic Microbial Niches in Cold Mountain Desert of Eastern Pamir (Tajikistan)

Microbial communities found in arid environments are commonly represented by biological soil crusts (BSCs) and endolithic assemblages. There is still limited knowledge concerning endoliths and BSCs occurring in the cold mountain desert of Pamir. The aim of the study was to investigate the composition and structure of endolithic bacterial communities in comparison to surrounding BSCs in three subregions of the Eastern Pamir (Tajikistan). The endolithic and BSC communities were studied using culture-independent and culture-dependent techniques. The structure of the endolithic bacterial communities can be characterized as Actinobacteria-Proteobacteria-Bacteroidetes-Chloroflexi-Cyanobacteria, while the BSCs' can be described as Proteobacteria-Actinobacteria-Bacteroidetes-Cyanobacteria assemblages with low representation of other bacteria. The endolithic cyanobacterial communities were characterized by the high percentage of Chroococcidiopsaceae, Nodosilineaceae, Nostocaceae and Thermosynechococcaceae, while in the BSCs were dominated by Nodosilineaceae, Phormidiaceae and Nostocaceae. The analysis of 16S rRNA genes of the cyanobacterial cultures revealed the presence of possibly novel species of Chroococcidiopsis, Gloeocapsopsis and Wilmottia. Despite the niches' specificity, which is related to the influence of microenvironment factors on the composition and structure of endolithic communities, our results illustrate the interrelation between the endoliths and the surrounding BSCs in some regions. The structure of cyanobacterial communities from BSC was the only one to demonstrate some subregional differences.

The sensitivity of multiple ecotoxicological assays for evaluating Microcystis aeruginosa cellular algal organic matter and contribution of cyanotoxins to the toxicity

Secondary metabolites of cyanobacteria and algae released during algal blooms often exhibit toxic effects, but only a small number of the metabolites are the subject of routine analytical screenings. Alternatively, ecotoxicological assays offer a better representation of the overall negative effects. The aim of this work was to compare multiple assays in their sensitivity towards cellular algal organic matter (COM) of the toxin-producing cyanobacterium Microcystis aeruginosa. Multiple endpoints were investigated: mortality, growth inhibition, bioluminescence inhibition, genotoxicity, endocrine-disrupting effects, oxidative stress, and the induction of ethoxyresorufin-O-deethylase (EROD). Three rainbow trout (Oncorhynchus mykiss) cell lines as well as representatives of bacteria, yeasts, algae, vascular plants, and crustaceans were employed, and the results were expressed per mg of dissolved organic carbon (DOC) in the COM. M. aeruginosa COM was toxic to the RTgill-W1, RTG-2, and RTL-W1 cell lines (EC₅₀ values ranging from 0.48 ± 0.02 to 1.9 ± 0.1 mg_DOC/L), to the crustacean Thamnocephalus platyurus (LC₅₀ = 20 ± 1 mg_DOC/L), and to Lepidium sativum (IC₅₀ = 241 ± 13 mg_DOC/L). In contrast, no effect was observed for bacteria and yeasts, and the growth of the alga Desmodesmus subspicatus was even stimulated. No genotoxicity, endocrine-disrupting effects or increase in oxidative stress or EROD activity was detected. The content of six microcystins (MC-LR, MC-RR, MC-YR, MC-LY, MC-LW, and MC-LF), anatoxin-a, cylindrospermopsin, and nodularin in the M. aeruginosa COM was determined by liquid chromatography-tandem mass spectrometry. An artificially prepared mixture of the detected cyanotoxins in the corresponding concentrations did not induce response in the O. mykiss cell lines and T. platyurus, suggesting that other cyanobacterial metabolites are responsible for the toxicity of M. aeruginosa.

Beyond Microcystins: Cyanobacterial Extracts Induce Cytoskeletal Alterations in Rice Root Cells

Microcystins (MCs) are cyanobacterial toxins and potent inhibitors of protein phosphatases 1 (PP1) and 2A (PP2A), which are involved in plant cytoskeleton (microtubules and F-actin) organization. Therefore, studies on the toxicity of cyanobacterial products on plant cells have so far been focused on MCs. In this study, we investigated the effects of extracts from 16 (4 MC-producing and 12 non-MC-producing) cyanobacterial strains from several habitats, on various enzymes (PP1, trypsin, elastase), on the plant cytoskeleton and H₂O₂ levels in Oryza sativa (rice) root cells. Seedling roots were treated for various time periods (1, 12, and 24 h) with aqueous cyanobacterial extracts and underwent either immunostaining for α-tubulin or staining of F-actin with fluorescent phalloidin. 2,7-dichlorofluorescein diacetate (DCF-DA) staining was performed for H₂O₂ imaging. The enzyme assays confirmed the bioactivity of the extracts of not only MC-rich (MC+), but also MC-devoid (MC−) extracts, which induced major time-dependent alterations on both components of the plant cytoskeleton. These findings suggest that a broad spectrum of bioactive cyanobacterial compounds, apart from MCs or other known cyanotoxins (such as cylindrospermopsin), can affect plants by disrupting the cytoskeleton.

The effects of microcystin-LR in Oryza sativa root cells: F-actin as a new target of cyanobacterial toxicity

Microcystins are toxins produced by cyanobacteria, notorious for negatively affecting a wide range of living organisms, among which several plant species. Although microtubules are a well-established target of microcystin toxicity, its effect on filamentous actin (F-actin) in plant cells has not yet been studied. Τhe effects of microcystin-LR (MC-LR) and an extract of a microcystin-producing freshwater cyanobacterial strain (Microcystis flos-aquae TAU-MAC 1510) on the cytoskeleton (F-actin and microtubules) of Oryza sativa (rice) root cells were studied with light, confocal, and transmission electron microscopy. Considering the role of F-actin in endomembrane system distribution, the endoplasmic reticulum and the Golgi apparatus in extract-treated cells were also examined. F-actin in both MC-LR- and extract-treated meristematic and differentiating root cells exhibited time-dependent alterations, ranging from disorientation and bundling to the formation of ring-like structures, eventually resulting in a collapse of the F-actin network after longer treatments. Disorganization and eventual depolymerization of microtubules, as well as abnormal chromatin condensation were observed following treatment with the extract, effects which could be attributed to microcystins and other bioactive compounds. Moreover, cell cycle progression was inhibited in extract-treated roots, specifically affecting the mitotic events. As a consequence of F-actin network disorganization, endoplasmic reticulum elements appeared stacked and diminished, while Golgi dictyosomes appeared aggregated. These results support that F-actin is a prominent target of MC-LR, both in pure form and as an extract ingredient. Endomembrane system alterations can also be attributed to the effects of cyanobacterial bioactive compounds (including microcystins) on the F-actin cytoskeleton.

The Marine Sponge Petrosia ficiformis Harbors Different Cyanobacteria Strains with Potential Biotechnological Application

Marine cyanobacteria are a source of bioactive natural compounds, with a wide range of biotechnological applications. However, information on sponge-associated cyanobacteria are relatively scarce to date. In this paper, we carried out the morphological and molecular characterization of eight cyanobacterial strains, previously isolated from the Mediterranean sponge Petrosia ficiformis, and evaluated their biological activities on epithelial- and neuron-like cultured cells of human and murine origin. The new analysis allowed maintaining the assignment of three strains (Cyanobium sp., Leptolyngbya ectocarpi, and Synechococcus sp.), while two strains previously identified as Synechococcus sp. and Leptolyngbya sp. were assigned to Pseudanabaena spp. One strain, i.e., ITAC104, and the ITAC101 strain corresponding to Halomicronema metazoicum, shared extremely high sequence identity, practically representing two clones of the same species. Finally, for only one strain, i.e., ITAC105, assignment to a specific genus was not possible. Concerning bioactivity analyses, incubation of cyanobacterial aqueous cell supernatants induced variable responses in cultured cells, depending on cell type, with some of them showing toxic activity on human epithelial-like cells and no toxic effects on human and rat neuron-like cells. Future investigations will allow to better define the bioactive properties of these cyanobacteria strains and to understand if they can be useful for (a) therapeutic purpose(s).

The Ascidian-Derived Metabolites with Antimicrobial Properties

Among the sub-phylum of Tunicate, ascidians represent the most abundant class of marine invertebrates, with 3000 species by heterogeneous habitat, that is, from shallow water to deep sea, already reported. The chemistry of these sessile filter-feeding organisms is an attractive reservoir of varied and peculiar bioactive compounds. Most secondary metabolites isolated from ascidians stand out for their potential as putative therapeutic agents in the treatment of several illnesses like microbial infections. In this review, we present and discuss the antibacterial activity shown by the main groups of ascidian-derived products, such as sulfur-containing compounds, meroterpenes, alkaloids, peptides, furanones, and their derivatives. Moreover, the direct evidence of a symbiotic association between marine ascidians and microorganisms shed light on the real producers of many extremely potent marine natural compounds. Hence, we also report the antibacterial potential, joined to antifungal and antiviral activity, of metabolites isolated from ascidian-associate microorganisms by culture-dependent methods.

β-Ν-Methylamino-L-alanine interferes with nitrogen assimilation in the cyanobacterium, non-BMAA producer, Synechococcus sp. TAU-MAC 0499

The production of β-Ν-methylamino-L-alanine (BMAA) in cyanobacteria is triggered by nitrogen-starvation conditions and its biological role, albeit unknown, is associated with nitrogen assimilation. In the present study, the effect of BMAA (773 μg L^-1) on nitrogen metabolism and physiology of the non-diazotrophic cyanobacterium and non-BMAA producer, Synechococcus sp. TAU-MAC 0499, was investigated. In order to study the combined effect of nitrogen availability and BMAA, nitrogen-starvation conditions were induced by transferring cells in nitrogen-free medium and subsequently exposing the cultures to BMAA. After short-term treatment (180 min) and in the presence of nitrogen, BMAA inhibited glutamine synthetase, which resulted in low concentration of glutamine. In the absence of nitrogen, although there was no effect on glutamine synthetase, a possible perturbation in nitrogen assimilation is reflected on the significant decrease in glutamate levels. During the long-term exposure (24-96 h), growth, photosynthetic pigments and total protein were not affected by BMAA exposure, except for an increase in protein and phycocyanin levels at 48 h in nitrogen replete conditions. Results suggest that BMAA interferes with nitrogen assimilation, in a different way, depending on the presence or absence of combined nitrogen, providing novel data on the potential biological role of BMAA.

New microginins from cyanobacteria of Greek freshwaters

Cyanobacteria can form extensive blooms in water with concurrent production and release of a large number of chemically diverse and bioactive metabolites, including hazardous toxins. Significant number of the metabolites belongs to non-ribosomal peptides, with unique residues, unusual structures and great potential for biotechnological application. The biosynthetic pathways of the peptides generate tens of variants, but only part of them has been identified. Microginins are an understudied class of cyanobacterial linear peptides with a characteristic decanoic acid derivative amino acid residue in their structure. In this study, cyanobacterial blooms and isolated strains from Greek lakes were analyzed for the presence of microginins by liquid chromatography coupled to hybrid triple quadrupole/linear ion trap mass spectrometer (LC-qTRAP MS/MS). Microginin structures were elucidated based on the obtained fragmentation spectra. A large number of microginins occurred in blooms of Greek freshwaters and the most frequently detected were Microginin FR1 (70% of samples), Microginin T1 (52%), Microginin 565B (52%), Microginin T2 (43%), and Microginin 565A (43%). Additionally, nine cyanobacterial strains i.e. Nostoc oryzae, Synechococcus sp., Microcystis aeruginosa, Microcystis viridis, and five Microcystis sp., were found to produce microginins. Thirty-six new microginin structures were characterized out of fifty-one totally detected variants. This is the first time that such a diversity of microginins is reported to be present in water bodies. Results clearly demonstrate the great metabolomic potential of cyanobacteria that inhabit Greek freshwaters and significantly expand the knowledge of cyanobacterial secondary metabolites with regards to the class of microginins.

Omics for Bioprospecting and Drug Discovery from Bacteria and Microalgae

"Omics" represent a combinatorial approach to high-throughput analysis of biological entities for various purposes. It broadly encompasses genomics, transcriptomics, proteomics, lipidomics, and metabolomics. Bacteria and microalgae exhibit a wide range of genetic, biochemical and concomitantly, physiological variations owing to their exposure to biotic and abiotic dynamics in their ecosystem conditions. Consequently, optimal conditions for adequate growth and production of useful bacterial or microalgal metabolites are critically unpredictable. Traditional methods employ microbe isolation and 'blind'-culture optimization with numerous chemical analyses making the bioprospecting process laborious, strenuous, and costly. Advances in the next generation sequencing (NGS) technologies have offered a platform for the pan-genomic analysis of microbes from community and strain downstream to the gene level. Changing conditions in nature or laboratory accompany epigenetic modulation, variation in gene expression, and subsequent biochemical profiles defining an organism's inherent metabolic repertoire. Proteome and metabolome analysis could further our understanding of the molecular and biochemical attributes of the microbes under research. This review provides an overview of recent studies that have employed omics as a robust, broad-spectrum approach for screening bacteria and microalgae to exploit their potential as sources of drug leads by focusing on their genomes, secondary metabolite biosynthetic pathway genes, transcriptomes, and metabolomes. We also highlight how recent studies have combined molecular biology with analytical chemistry methods, which further underscore the need for advances in bioinformatics and chemoinformatics as vital instruments in the discovery of novel bacterial and microalgal strains as well as new drug leads.

Limited Microcystin, Anatoxin and Cylindrospermopsin Production by Cyanobacteria from Microbial Mats in Cold Deserts

Toxic metabolites are produced by many cyanobacterial species. There are limited data on toxigenic benthic, mat-forming cyanobacteria, and information on toxic cyanobacteria from Central Asia is even more scarce. In the present study, we examined cyanobacterial diversity and community structure, the presence of genes involved in toxin production and the occurrence of cyanotoxins in cyanobacterial mats from small water bodies in a cold high-mountain desert of Eastern Pamir. Diversity was explored using amplicon-based sequencing targeting the V3-V4 region of the 16S rRNA gene, toxin potential using PCR-based methods (mcy, nda, ana, sxt), and toxins by enzyme-linked immunosorbent assays (ELISAs) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). Molecular identification of cyanobacteria showed a high similarity of abundant taxa to Nostoc PCC-73102, Nostoc PCC-7524, Nodularia PCC-935 and Leptolyngbya CYN68. The PCRs revealed the presence of mcyE and/or ndaF genes in 11 samples and mcyD in six. The partial sequences of the mcyE gene showed high sequence similarity to Nostoc, Planktothrix and uncultured cyanobacteria. LC-MS/MS analysis identified six microcystin congeners in two samples and unknown peptides in one. These results suggest that, in this extreme environment, cyanobacteria do not commonly produce microcystins, anatoxins and cylindrospermopsins, despite the high diversity and widespread occurrence of potentially toxic taxa.

Bioprospecting Sponge-Associated Marine Cyanobacteria to Produce Bioactive Compounds

Marine cyanobacteria are considered a prolific source of bioactive natural products with a range of biotechnological and pharmacological applications. However, data on the production of natural compounds from sponge-associated cyanobacteria are scarce. This study aimed to assess the potential of sponge-associated cyanobacteria strains representing different taxonomic groups for the production of bioactive compounds and the biological activity of their extracts. Phylogenetic analysis of sponge-associated cyanobacteria and screening for the presence of genes encoding non-ribosomal peptide synthetases (NRPSs) and polyketide synthases (PKSs) were performed. Methanol extracts of the sponge-associated strains were analyzed for cyanotoxin production and tested for antioxidant activity and cytotoxic activity against several human cancer cell lines and pathogenic bacteria. PKS were detected in all sponge-associated strains examined, indicating the metabolic potential of the isolates. PKS genes were more ubiquitous than NRPS genes. Cyanotoxins (i.e., cylindrospermopsin, anatoxin-a, nodularin, and microcystins) were not detected in any of the sponge-associated cyanobacterial strains. Strains belonging to Leptothoe, Pseudanabaena, and Synechococcus were found to have activity mainly against Staphylococcus aureus. In addition, sponge-associated Leptothoe strains (TAU-MAC 0915, 1015, 1115, and 1215) were found to be highly cytotoxic and in most cases more effective against human cancer cell lines than against normal cells. Extracts with the most promising bioactivity deserve further investigation in order to isolate and identify the bioactive molecule(s).