Cyanopeptolins, depsipeptides from cyanobacteria

Structure, Toxicity, Prevalence, and Degradation of Six Understudied Freshwater Cyanopeptides

Anthropogenic influences have increased global warming and eutrophication, escalating the frequency and severity of harmful cyanobacterial blooms (cHABs) in freshwater ecosystems. These blooms release cyanopeptides, a diverse class of bioactive compounds with varying acute and chronic toxicities upon ingestion. To date, research has prioritized acutely toxic cyanopeptides like microcystins. As a result, significantly less is known about other freshwater cyanopeptides. This review highlights six understudied cyanopeptide classes, anabaenopeptins, cyanopeptolins, aeruginosamides, aeruginosins, microginins, and cyclamides, and provides a comprehensive overview of their molecular structures, toxicological profiles, environmental concentrations, and known degradation pathways. Given the potential toxicity, increased environmental abundance, and environmental stability of many cyanopeptides in freshwater sources, further research is needed to understand if degraded cyanopeptides are still biologically active prior to entering drinking water to ensure public health.

Unraveling the functional dynamics of Caenorhabditis elegans stress-responsive omega class GST-44

Glutathione transferases from the omega class are notable for their roles in redox regulation and cellular stress response. In this study, we conducted a comprehensive functional characterization of GST-44, an omega-class glutathione S-transferase (GSTO), in Caenorhabditis elegans, focusing on its role in cellular defense mechanisms against stress. Biochemical analysis revealed GSTO-specific enzymatic activities of recombinant GST-44, including dehydroascorbate reductase, thioltransferase, and arsenate reductase activities. Using transgenic GFP reporter strains, we identified predominant expression of GST-44 in the intestine and excretory H-cell, with significant upregulation observed under diverse stress conditions. Induction of GST-44 was particularly pronounced in the intestine in response to pathogen-, oxidative-, and endoplasmic reticulum stress. Notably, under arsenic stress, the expression of gst-44 was significantly upregulated in the excretory system of the worm, underscoring its critical role in mediating arsenic detoxification. Moreover, we demonstrated the induction of GST-44 using dimethyl fumarate, a highly specific mammalian Nrf-2 activator. The upregulation of GST-44 during arsenic stress was dependent not only on the oxidative stress response transcription factor SKN-1/Nrf2 but also on PHA-4. The deletion mutant strain gst-44(tm6133) exhibited reduced stress resistance and a shortened lifespan, with a highly diminished survival rate under arsenic stress compared to other CRISPR-generated C. elegans GSTO deletion mutants. Our findings highlight the essential role of GST-44 in mediating arsenic detoxification, as well as in stress adaptation and defense mechanisms in C. elegans.

Negative Effects of Cyanotoxins and Adaptative Responses of Daphnia

The plethora of cyanobacterial toxins are an enormous threat to whole ecosystems and humans. Due to eutrophication and increases in lake temperatures from global warming, changes in the distribution of cyanobacterial toxins and selection of few highly toxic species/ strains are likely. Globally, one of the most important grazers that controls cyanobacterial blooms is Daphnia, a freshwater model organism in ecology and (eco)toxicology. Daphnia-cyanobacteria interactions have been studied extensively, often focusing on the interference of filamentous cyanobacteria with Daphnia's filtering apparatus, or on different nutritional constraints (the lack of essential amino acids or lipids) and grazer toxicity. For a long time, this toxicity only referred to microcystins. Currently, the focus shifts toward other deleterious cyanotoxins. Still, less than 10% of the total scientific output deals with cyanotoxins that are not microcystins; although these other cyanotoxins can occur just as frequently and at similar concentrations as microcystins in surface water. This review discusses the effects of different cyanobacterial toxins (hepatotoxins, digestive inhibitors, neurotoxins, and cytotoxins) on Daphnia and provides an elaborate and up-to-date overview of specific responses and adaptations of Daphnia. Furthermore, scenarios of what we can expect for the future of Daphnia-cyanobacteria interactions are described by comprising anthropogenic threats that might further increase toxin stress in Daphnia.

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.

Phytoplankton of the Curonian Lagoon as a New Interesting Source for Bioactive Natural Products. Special Impact on Cyanobacterial Metabolites

The bioprospecting of marine and brackish water systems has increased during the last decades. In this respect, microalgae, including cyanobacteria, and their metabolites are one of the most widely explored resources. Most of the bioactive compounds are isolated from ex situ cultures of microorganisms; however, analysis of field samples could also supply valuable information about the metabolic and biotechnological potential of microalgae communities. In this work, the activity of phytoplankton samples from the Curonian Lagoon was studied. The samples were active against antibiotic resistant clinical and environmental bacterial strains as well as against serine proteases and T47D human breast adenocarcinoma cells. No significant effect was found on Daphnia magna. In addition, using LC-MS/MS, we documented the diversity of metabolites present in field samples. A list of 117 detected cyanopeptides was presented. Cyanopeptolins constituted the largest class of cyanopeptides. As complex bloom samples were analyzed, no link between the observed activity and a specific sample component can be established. However, the results of the study showed a biotechnological potential of natural products from the Curonian Lagoon.

From dolastatin 13 to cyanopeptolins, micropeptins, and lyngbyastatins: the chemical biology of Ahp-cyclodepsipeptides

Covering: 1989 up to 2019 Ahp-cyclodepsipeptides (also known as Ahp-containing cyclodepsipeptides, cyanopeptolins, micropeptins, microginines, and lyngbyastatins, and by many other names) are a family of non-ribosomal peptide synthesis (NRPS)-derived natural products with potent serine protease inhibitory properties. Here, we review their isolation and structural elucidation from natural sources as well as studies of their biosynthesis, molecular mode of action, and use in drug discovery efforts. Accordingly, this summary aims to provide a comprehensive overview of the current state-of-the-art Ahp-cyclodepsipeptide research.

Insight into Unprecedented Diversity of Cyanopeptides in Eutrophic Ponds Using an MS/MS Networking Approach

Man-made shallow fishponds in the Czech Republic have been facing high eutrophication since the 1950s. Anthropogenic eutrophication and feeding of fish have strongly affected the physicochemical properties of water and its aquatic community composition, leading to harmful algal bloom formation. In our current study, we characterized the phytoplankton community across three eutrophic ponds to assess the phytoplankton dynamics during the vegetation season. We microscopically identified and quantified 29 cyanobacterial taxa comprising non-toxigenic and toxigenic species. Further, a detailed cyanopeptides (CNPs) profiling was performed using molecular networking analysis of liquid chromatography-tandem mass spectrometry (LC-MS/MS) data coupled with a dereplication strategy. This MS networking approach, coupled with dereplication, on the online global natural product social networking (GNPS) web platform led us to putatively identify forty CNPs: fourteen anabaenopeptins, ten microcystins, five cyanopeptolins, six microginins, two cyanobactins, a dipeptide radiosumin, a cyclooctapeptide planktocyclin, and epidolastatin 12. We applied the binary logistic regression to estimate the CNPs producers by correlating the GNPS data with the species abundance. The usage of the GNPS web platform proved a valuable approach for the rapid and simultaneous detection of a large number of peptides and rapid risk assessments for harmful blooms.

Tutuilamides A-C: Vinyl-Chloride-Containing Cyclodepsipeptides from Marine Cyanobacteria with Potent Elastase Inhibitory Properties

Marine cyanobacteria (blue-green algae) have been shown to possess an enormous capacity to produce structurally diverse natural products that exhibit a broad spectrum of potent biological activities, including cytotoxic, antifungal, antiparasitic, antiviral, and antibacterial activities. Using mass-spectrometry-guided fractionation together with molecular networking, cyanobacterial field collections from American Samoa and Palmyra Atoll yielded three new cyclic peptides, tutuilamides A-C. Their structures were established by spectroscopic techniques including 1D and 2D NMR, HR-MS, and chemical derivatization. Structure elucidation was facilitated by employing advanced NMR techniques including nonuniform sampling in combination with the 1,1-ADEQUATE experiment. These cyclic peptides are characterized by the presence of several unusual residues including 3-amino-6-hydroxy-2-piperidone and 2-amino-2-butenoic acid, together with a novel vinyl chloride-containing residue. Tutuilamides A-C show potent elastase inhibitory activity together with moderate potency in H-460 lung cancer cell cytotoxicity assays. The binding mode to elastase was analyzed by X-ray crystallography revealing a reversible binding mode similar to the natural product lyngbyastatin 7. The presence of an additional hydrogen bond with the amino acid backbone of the flexible side chain of tutuilamide A, compared to lyngbyastatin 7, facilitates its stabilization in the elastase binding pocket and possibly explains its enhanced inhibitory potency.

Daphnia magna Exudates Impact Physiological and Metabolic Changes in Microcystis aeruginosa

While the intracellular function of many toxic and bioactive cyanobacterial metabolites is not yet known, microcystins have been suggested to have a protective role in the cyanobacterial metabolism, giving advantage to toxic over nontoxic strains under stress conditions. The zooplankton grazer Daphnia reduce cyanobacterial dominance until a certain density, which may be supported by Daphnia exudates, affecting the cyanobacterial physiological state and metabolites’ production. Therefore, we hypothesized that D. magna spent medium will impact the production of cyanobacterial bioactive metabolites and affect cyanobacterial photosynthetic activity in the nontoxic, but not the toxic strain. Microcystin (MC-LR and des-MC-LR) producing M. aeruginosa PCC7806 and its non-microcystin producing mutant were exposed to spent media of different D. magna densities and culture durations. D. magna spent medium of the highest density (200/L) cultivated for the shortest time (24 h) provoked the strongest effect. D.magna spent medium negatively impacted the photosynthetic activity of M. aeruginosa PCC7806, as well as the dynamics of intracellular and extracellular cyanobacterial metabolites, while its mutant was unaffected. In the presence of Daphnia medium, microcystin does not appear to have a protective role for the strain. On the contrary, extracellular cyanopeptolin A increased in M. aeruginosa PCC7806 although the potential anti-grazing role of this compound would require further studies.

Cyanobacterial bioactive metabolites-A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1-3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds. Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.

Automated Subdaily Sampling of Cyanobacterial Toxins on a Buoy Reveals New Temporal Patterns in Toxin Dynamics

Temporal variability of toxins produced by cyanobacteria in lakes is relatively unknown at time scales relevant to public health (i.e., hourly). In this study, a water quality monitoring buoy was outfitted with an automated water sampler taking preserved samples every 6 h for 68.75 days over a drinking water intake. A total of 251 samples were analyzed by tandem mass spectrometry for 21 cyanotoxin congeners in 5 classes producing 5020 data points. Microcystins (MCs) were the most abundant toxins measured (mean ± sd = 3.9 ± 3.3 μg/L) followed by cyanopeptolins (CPs) (1.1 ± 1.5 μg/L), anabaenopeptins (APs) (1.0 ± 0.6 μg/L), anatoxin-a (AT-A) (0.03 ± 0.06 μg/L), and microginin-690 (MG-690) (0.002 ± 0.01 μg/L). Advanced time series analyses uncovered patterns in cyanotoxin production. The velocity of cyanotoxin concentration varied from -0.7 to 0.9 μg/L/h with a maximum positive velocity just prior to peak toxin concentration during nonbloom periods. A backward-looking moving window of variance analysis detected major increases in cyanotoxin concentration and predicted the two greatest increases in MC. A wavelet analysis identified a significant ( p < 0.01) 2.8-4.2 day periodicity in toxin concentration over a ∼25 day period during peak toxin production, which is partially explained by easterly wind velocity ( R = -0.2, p < 0.05). Diversity in congener profiles was explored with principle component analysis showing that cyanotoxin dynamics followed a seasonal trajectory where toxin profiles were significantly clustered (ANOSIM R = 0.7, p < 0.05) on a daily basis. Variability in toxin profiles was strongly correlated with time ( R = -0.8, p < 0.001) as well as the C:N ratio of the toxin pool ( R = 0.17, p < 0.05). The methods employed here should be useful for uncovering patterns in cyanotoxin dynamics in other systems.

Cyanobacterial bioactive metabolites-A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1-3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds. Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.

Cyanopeptolins with Trypsin and Chymotrypsin Inhibitory Activity from the Cyanobacterium Nostoc edaphicum CCNP1411

Cyanopeptolins (CPs) are one of the most frequently occurring cyanobacterial peptides, many of which are inhibitors of serine proteases. Some CP variants are also acutely toxic to aquatic organisms, especially small crustaceans. In this study, thirteen CPs, including twelve new variants, were detected in the cyanobacterium Nostoc edaphicum CCNP1411 isolated from the Gulf of Gdańsk (southern Baltic Sea). Structural elucidation was performed by tandem mass spectrometry with verification by NMR for CP962 and CP985. Trypsin and chymotrypsin inhibition assays confirmed the significance of the residue adjacent to 3-amino-6-hydroxy-2-piperidone (Ahp) for the activity of the peptides. Arginine-containing CPs (CPs-Arg²) inhibited trypsin at low IC₅₀ values (0.24⁻0.26 &micro;M) and showed mild activity against chymotrypsin (IC₅₀ 3.1⁻3.8 &micro;M), while tyrosine-containing CPs (CPs-Tyr²) were selectively and potently active against chymotrypsin (IC₅₀ 0.26 &micro;M). No degradation of the peptides was observed during the enzyme assays. Neither of the CPs were active against thrombin, elastase or protein phosphatase 1. Two CPs (CP962 and CP985) had no cytotoxic effects on MCF-7 breast cancer cells. Strong and selective activity of the new cyanopeptolin variants makes them potential candidates for the development of drugs against metabolic disorders and other diseases.

Interspecific differences between D. pulex and D. magna in tolerance to cyanobacteria with protease inhibitors

It is known that cyanobacteria negatively affect herbivores due to their production of toxins such as protease inhibitors. In the present study we investigated potential interspecific differences between two major herbivores, Daphnia magna and Daphnia pulex, in terms of their tolerance to cyanobacteria with protease inhibitors. Seven clones each of D. magna and of D. pulex were isolated from different habitats in Europe and North America. To test for interspecific differences in the daphnids’ tolerance to cyanobacteria, their somatic and population growth rates were determined for each D. magna and D. pulex clone after exposure to varying concentrations of two Microcystis aeruginosa strains. The M. aeruginosa strains NIVA and PCC⁻ contained either chymotrypsin or trypsin inhibitors, but no microcystins. Mean somatic and population growth rates on a diet with 20% NIVA were significantly more reduced in D. pulex than in D. magna. On a diet with 10% PCC⁻, the population growth of D. pulex was significantly more reduced than that of D. magna. This indicates that D. magna is more tolerant to cyanobacteria with protease inhibitors than D. pulex. The reduction of growth rates was possibly caused by an interference of cyanobacterial inhibitors with proteases in the gut of Daphnia, as many other conceivable factors, which might have been able to explain the reduced growth, could be excluded as causal factors. Protease assays revealed that the sensitivities of chymotrypsins and trypsins to cyanobacterial protease inhibitors did not differ between D. magna and D. pulex. However, D. magna exhibited a 2.3-fold higher specific chymotrypsin activity than D. pulex, which explains the observed higher tolerance to cyanobacterial protease inhibitors of D. magna. The present study suggests that D. magna may control the development of cyanobacterial blooms more efficiently than D. pulex due to differences in their tolerance to cyanobacteria with protease inhibitors.

Cyanobacterial protease inhibitors lead to maternal transfer of increased protease gene expression in Daphnia

Protease inhibitors (PIs) have frequently been found in cyanobacterial blooms and have been shown to affect the major herbivore Daphnia by decreasing growth and inhibiting gut protease activity. However, it has been shown that a clone of Daphnia is able to respond to dietary PIs by increasing its protease gene expression. Such an inducible response might be maternally transferred to the next generation. Therefore, we tested a tolerant clone for maternal transfer of protease gene expression. When exposed to the trypsin inhibitor-producing cyanobacterium Microcystis aeruginosa PCC7806 Mut, Daphnia mothers and their untreated newborns showed an increase in trypsin gene expression compared to naïve mothers grown on control food and their offspring. The maternally transferred increase in gene expression was accompanied by a higher somatic growth rate of the offspring generation from exposed mothers compared to offspring from naïve mothers. This higher growth rate compensated for the lower dry mass of newborns from exposed mothers and led to the same fitness as observed in the offspring of naïve mothers. In nature, clones that can maternally transfer increased protease gene expression should have an advantage over clones that cannot. The selection for such more tolerant clones by naturally occurring PIs might lead to microevolution of natural Daphnia populations, and to local adaptation in the long term. This is the first study to show an adaptive maternal transfer of increased target gene expression in an ecological context.

Molecular mechanisms of tolerance to cyanobacterial protease inhibitors revealed by clonal differences in Daphnia magna

Protease inhibitors of primary producers are a major food quality constraint for herbivores. In nutrient-rich freshwater ecosystems, the interaction between primary producers and herbivores is mainly represented by Daphnia and cyanobacteria. Protease inhibitors have been found in many cyanobacterial blooms. These inhibitors have been shown (both in vitro and in situ) to inhibit the most important group of digestive proteases in the daphnid's gut, that is, trypsins and chymotrypsins. In this study, we fed four different Daphnia magna genotypes with the trypsin-inhibitor-containing cyanobacterial strain Microcystis aeruginosa PCC 7806 Mut. Upon exposure to dietary trypsin inhibitors, all D. magna genotypes showed increased gene expression of digestive trypsins and chymotrypsins. Exposure to dietary trypsin inhibitors resulted in increased activity of chymotrypsins and reduced activity of trypsin. Strong intraspecific differences in tolerance of the four D. magna genotypes to the dietary trypsin inhibitors were found. The degree of tolerance depended on the D. magna genotype. The genotypes' tolerance was positively correlated with the residual trypsin activity and the different IC(50) values of the trypsins. On the genetic level, the different trypsin loci varied between the D. magna genotypes. The two tolerant Daphnia genotypes that both originate from the same lake, which frequently produces cyanobacterial blooms, clustered in a neighbour-joining phylogenetic tree based on the three trypsin loci. This suggests that the genetic variability of trypsin loci was an important cause for the observed intraspecific variability in tolerance to cyanobacterial trypsin inhibitors. Based on these findings, it is reasonable to assume that such genetic variability can also be found in natural populations and thus constitutes the basis for local adaptation of natural populations to dietary protease inhibitors.

Inducible tolerance to dietary protease inhibitors in Daphnia magna

Daphnia has been shown to acquire tolerance to cyanobacterial toxins within an animals' lifetime and to transfer this tolerance to the next generation. Here we used a strain of the cyanobacterium Microcystis aeruginosa, which contained two chymotrypsin inhibitors (BN920 and CP954), the green alga Scenedesmus obliquus as reference food and a clone of D. magna to investigate the physiological mechanism of acquired tolerance to these cyanobacterial toxins. The intracellular concentrations of CP954 and BN920 were 1550 and 120 μmol l–1, respectively. When food suspensions of the green alga contained &gt;60% M. aeruginosa, growth rates of D. magna were reduced. When grown on the green alga, three chymotrypsins ranging in mass from 16 to 22 kDa were distinguished in D. magna. Purified BN920 and CP954 specifically inhibited D. magna chymotrypsins. Feeding with encapsulated BN920 resulted in growth depression in D. magna and replacement of the chymotrypsins by three chymotrypsins with smaller molecular mass. With just 20% M. aeruginosa, the same changes in the chymotrypsin pattern as with the pure inhibitor were observed. IC50 values for inhibition of chymotrypsins of D. magna growing on the green alga were 5.4 nmol l–1 (BN920) and 7.4 nmol l–1 (CP954). When D. magna was grown on 20% M. aeruginosa, 2.2-fold higher IC50 values were observed. This indicated that increased tolerance to these dietary inhibitors was acquired within an animal's lifetime by remodelling the digestive chymotrypsins, which in turn serves as an intra-generational defence against these cyanobacterial inhibitors. This mechanism might be relevant for the transfer of tolerance to the next generation through maternal effects.

Characterization of the locus of genes encoding enzymes producing heptadepsipeptide micropeptin in the unicellular cyanobacterium Microcystis

The gene cluster involved in producing the cyclic heptadepsipeptide micropeptin was cloned from the genome of the unicellular cyanobacterium Microcystis aeruginosa K-139. Sequencing revealed four genes encoding non-ribosomal peptide synthetases (NRPSs) that are highly similar to the gene cluster involved in cyanopeptolins biosynthesis. According to predictions based on the non-ribosomal consensus code, the order of the mcnABCE NPRS modules was well consistent with that of the biosynthetic assembly of cyclic peptides. The biochemical analysis of a McnB(K-139) adenylation domain and the knock-out of mcnC in a micropeptin-producing strain, M. viridis S-70, revealed that the mcn gene clusters were responsible for the production of heptadepsipeptide micropeptins. A detailed comparison of nucleotide sequences also showed that the regions between the mcnC and mcnE genes of M. aeruginosa K-139 retained short stretches of DNA homologous to halogenase genes involved in the synthesis of halogenated cyclic peptides of the cyanopeptolin class including anabaenopeptilides. This suggests that the mcn clusters of M. aeruginosa K-139 have lost the halogenase genes during evolution. Finally, a comparative bioinformatics analysis of the congenial gene cluster for depsipetide biosynthesis suggested the diversification and propagation of the NRPS genes in cyanobacteria.

Depsipeptides from a Guamanian Marine Cyanobacterium, Lyngbya bouillonii, with Selective Inhibition of Serine Proteases

Bouillomides A (1) and B (2) are two depsipeptide analogues of dolastatin 13. Isolated from a Guamanian sample of Lyngbya bouillonii, the planar structures were elucidated on the basis of HR-ESI-MS and NMR data, while the absolute configurations were determined by employing functional group conversions, modified Marfey's analysis, and detailed analyses of ROESY correlations. Compounds 1 and 2 selectively inhibited serine proteases elastase (IC(50) = 1.9 μM for both) and chymotrypsin (IC(50) = 0.17 and 9.3 μM, respectively) while showing no inhibition of trypsin (IC(50) > 100 μM).

New peptolides from the cyanobacterium Nostoc insulare as selective and potent inhibitors of human leukocyte elastase

Eight new cyanopeptolins (insulapeptolides A-H) were obtained from the cyanobacterium Nostoc insulare. Their isolation was guided by their bioactivity toward the target enzyme human leukocyte elastase, molecular biological investigations, and MALDI-TOF analysis. These peptides are selective inhibitors of human leukocyte elastase with activities in the nanomolar range. Insulapeptolide D was the most potent compound with an IC(50) value of 85 nM (K(i) value of 36 nM).

Recombination and selectional forces in cyanopeptolin NRPS operons from highly similar, but geographically remote Planktothrix strains

Background

Cyanopeptolins are nonribosomally produced heptapetides showing a highly variable composition. The cyanopeptolin synthetase operon has previously been investigated in three strains from the genera Microcystis, Planktothrix and Anabaena. Cyanopeptolins are displaying protease inhibitor activity, but the biological function(s) is (are) unknown. Cyanopeptolin gene cluster variability and biological functions of the peptide variants are likely to be interconnected.

Results

We have investigated two cyanopeptolin gene clusters from highly similar, but geographically remote strains of the same genus. Sequencing of a nonribosomal peptide synthetase (NRPS) cyanopeptolin gene cluster from the Japanese strain Planktothrix NIES 205 (205-oci), showed the 30 kb gene cluster to be highly similar to the oci gene cluster previously described in Planktothrix NIVA CYA 116, isolated in Norway. Both operons contained seven NRPS modules, a sulfotransferase (S) and a glyceric acid loading (GA)-domain. Sequence analyses showed a high degree of conservation, except for the presence of an epimerase domain in NIES 205 and the regions around the epimerase, showing high substitution rates and Ka/Ks values above 1. The two strains produce almost identical cyanopeptolins, cyanopeptolin-1138 and oscillapeptin E respectively, but with slight differences regarding the production of minor cyanopeptolin variants. These variants may be the result of relaxed adenylation (A)-domain specificity in the nonribosomal enzyme complex. Other genetic markers (16S rRNA, ntcA and the phycocyanin cpcBA spacer) were identical, supporting that these geographically separated Planktothrix strains are closely related.

Conclusion

A horizontal gene transfer event resulting in exchange of a whole module-encoding region was observed. Nucleotide statistics indicate that both purifying selection and positive selection forces are operating on the gene cluster. The positive selection forces are acting within and around the epimerase insertion while purifying selection conserves the remaining (major) part of the gene cluster. The presence of an epimerase in the gene cluster is in line with the D-configuration of Htyr, determined experimentally in oscillapeptin E in a previous study.

Comparison of cyanopeptolin genes in Planktothrix, Microcystis, and Anabaena strains: evidence for independent evolution within each genus

The major cyclic peptide cyanopeptolin 1138, produced by Planktothrix strain NIVA CYA 116, was characterized and shown to be structurally very close to the earlier-characterized oscillapeptin E. A cyanopeptolin gene cluster likely to encode the corresponding peptide synthetase was sequenced from the same strain. The 30-kb oci gene cluster contains two novel domains previously not detected in nonribosomal peptide synthetase gene clusters (a putative glyceric acid-activating domain and a sulfotransferase domain), in addition to seven nonribosomal peptide synthetase modules. Unlike in two previously described cyanopeptolin gene clusters from Anabaena and Microcystis, a halogenase gene is not present. The three cyanopeptolin gene clusters show similar gene and domain arrangements, while the binding pocket signatures deduced from the adenylation domain sequences and the additional tailoring domains vary. This suggests loss and gain of tailoring domains within each genus, after the diversification of the three clades, as major events leading to the present diversity. The ABC transporter genes associated with the cyanopeptolin gene clusters form a monophyletic clade and accordingly are likely to have evolved as part of the functional unit. Phylogenetic analyses of adenylation and condensation domains, including domains from cyanopeptolins and microcystins, show a closer similarity between the Planktothrix and Microcystis cyanopeptolin domains than between these and the Anabaena domain. No clear evidence of recombination between cyanopeptolins and microcystins could be detected. There were no strong indications of horizontal gene transfer of cyanopeptolin gene sequences across the three genera, supporting independent evolution within each genus.

Binding structure of the leucine aminopeptidase inhibitor microginin FR1

Natural bioactive compounds are of general interest for pharmaceutical research because they may serve as leads in drug development campaigns. Among them, microginins are linear peptides known to inhibit various exopeptidases. The crystal structure of microginin FR1 from Microcystis sp. bound to bovine lens leucine aminopeptidase was established at 1.73 Angstrom resolution. The observed binding structure could be beneficial for the design of potent aminopeptidase inhibitors.

Antifouling potential of cyanobacteria: a mini-review

Cyanobacteria produce a variety of bioactive metabolites that may have allelochemical functions in the natural environment, such as in the prevention of fouling by colonising organisms. Chemical compounds from cyanobacteria are also of biotechnological interest, especially for clinical applications, because of their antibiotic, algicidal, cytotoxic, immunosupressive and enzyme inhibiting activities. Cyanobacterial metabolites have the potential for use in antifouling technology, since they show antibacterial, antialgal, antifungal and antimacrofouling properties which could be expoited in the prevention of biofouling on man-made substrata in the aquatic environment. Molecules with antifouling activity represent a number of types including fatty acids, lipopeptides, amides, alkaloids, terpenoids, lactones, pyrroles and steroids. The isolation of biogenic compounds and the determination of their structure may provide leads for future development of, for example, environmentally friendly antifouling paints. An advantage of exploring the efficacy of cyanobacterial products is that the organisms can be grown in mass culture, which can be manipulated to achieve optimal production of bioactive substances. Phycotoxins and related products from cyanobacteria may serve as materials for antimicro- and antimacrofouling applications. A survey of antibiotic compounds with antifouling potential revealed more than 21 different antifouling substances from 27 strains of cyanobacteria.

Cyanopeptolin 954, a chlorine-containing chymotrypsin inhibitor of Microcystis aeruginosa NIVA Cya 43

A new depsipeptide, cyanopeptolin 954 (1), was isolated from the freshwater cyanobacterium Microcystis aeruginosa NIVA Cya 43. The structure of the compound was elucidated by chemical and spectroscopic analyses, including 2D NMR and GC-MS of the hydrolysate. The major structural differences compared to previously characterized heptadepsipeptides of Microcystis are the replacement of the basic amino acid in position 4 by L-leucine, the presence of L-phenylalanine in position 6, and the uncommon residue 3'-chloro-N-Me-L-tyrosine in position 7. Cyanopeptolin 954 inhibited chymotrypsin with an IC50 value of 45 nM. Nostopeptin BN920, formerly isolated from the cyanobacterium Nostoc,(1) was isolated from the same strain of Microcystis, and a cis amide bond between Phe (6) and N-Me-Tyr (7) was shown. Nostopeptin BN920 inhibited chymotrypsin with an IC50 value of 31 nM.

Characterization of proteases in guts of Daphnia magna and their inhibition by Microcystis aeruginosa PCC 7806

Many cyanobacteria produce peptides that inhibit mammalian proteases. The hypothesis that inhibitors of mammalian proteases produced by cyanobacteria also interfere with digestive proteases of natural cladoceran grazers was tested by comparing the effects of cyanobacterial protease inhibitors on digestive proteases from Daphnia magna and on commercially available bovine proteases. The major digestive proteases of D. magna are trypsins and chymotrypsins, which differ from those of bovine origin in substrate specificity and susceptibility to synthetic inhibitors. An extract from Microcystis aeruginosa strain PCC 7806 inhibited both types of D. magna proteases. Subsequent fractionation of the extract by high-performance liquid chromatography indicated that several inhibitors are produced by M. aeruginosa that differ in their specificity for the trypsins and chymotrypsins of D. magna. Two fractions differed in their inhibitory effect on proteases of D. magna and bovine origin; therefore, assessment of the impact of cyanobacterial protease inhibitors on natural communities requires the use of digestive proteases from ecologically relevant grazers.

Cysteine and serine protease-mediated proteolysis in body homogenate of a zooplankter, Moina macrocopa, is inhibited by the toxic cyanobacterium, Microcystis aeruginosa PCC7806

The paper describes the characterization of proteases in the whole body homogenate of Moina macrocopa, which can possibly be inhibited by the extracts of Microcystis aeruginosa PCC7806. With the use of oligopeptide substrates and specific inhibitors, we detected the activities of trypsin, chymotrypsin, elastase and cysteine protease. Cysteine protease, the predominant enzyme behind proteolysis of a natural substrate, casein, was partially purified by gel filtration. The substrate SDS-polyacrylamide gel electrophoresis of body homogenate revealed the presence of nine bands of proteases (17-72 kDa). The apparent molecular mass of an exclusive cysteine protease was 60 kDa, whereas of trypsin, it was 17-24 kDa. An extract of M. aeruginosa PCC7806 significantly inhibited the activities of trypsin, chymotrypsin and cysteine protease in M. macrocopa body homogenate at estimated IC(50) of 6- to 79-microg dry mass mL(-1). Upon fractionation by C-18 solid-phase extraction, 60% methanolic elute contained all the protease inhibitors, and these metabolites could be further separated by reverse-phase liquid chromatography. The metabolites inhibitory to M. macrocopa proteases also inhibited the corresponding class of proteases of mammalian/plant origin. The study suggests that protease inhibition may contribute to chemical interaction of cyanobacteria and crustacean zooplankton.

Protease activity in gut of Daphnia magna: evidence for trypsin and chymotrypsin enzymes

Two major protease activities were present in gut homogenates of the cladoceran crustacean Daphnia magna: (i) a trypsin activity that hydrolysed the synthetic substrate N-benzoyl-dl-arginine p-nitroanilide and was strongly inhibited by N-p-tosyl-lysine chloroketone (TLCK) and 4-(amidinophenyl)methanesulfonyl fluoride (APMSF) and not inhibited by chymostatin; and (ii) a chymotrypsin activity that hydrolysed synthetic chymotrypsin substrates containing more than one amino acid, did not hydrolyse N-benzoyl-l-tyrosine p-nitroanilide, and was strongly inhibited by chymostatin and not by TLCK and APMSF. Both activities had alkaline pH optima (pH 7-10), but were shown to be due to distinct types of proteases. These two enzyme activities accounted for 75-83% of the proteolytic activity of gut contents. Substrate SDS-polyacrylamide gel electrophoresis revealed nine different proteases ranging from 15 to 73 kDa.

Hepatotoxic cyanobacteria: a review of the biological importance of microcystins in freshwater environments

Cyanobacteria possess many adaptations to develop population maxima or "blooms" in lakes and reservoirs. A potential consequence of freshwater blooms of many cyanobacterial species is the production of potent toxins, including the cyclic hepatotoxins, microcystins (MCs). Approximately 70 MC variants have been isolated. Their toxicity to humans and other animals is well studied, because of public health concerns. This review focuses instead on the production and degradation of MCs in freshwater environments and their effects on aquatic organisms. Genetic research has revealed the existence of MC-related genes, yet the expression of these genes seems to be regulated by complex mechanisms and is influenced by environmental factors. In natural water bodies, the species composition of cyanobacterial communities and the ratio of toxic to nontoxic species and strains are largely responsible for total toxin production. Cyanobacteria play vital roles in aquatic food webs, yet production, accumulation, and toxicity patterns of MCs within aquatic food webs remain obscure.

Two new chymotrypsin inhibitors isolated from the Cyanobacterium Microcystis aeruginosa NIES-88

Micropeptins 88-N (1) and 88-Y (2), new 3-amino-6-hydroxy-2-piperidone (Ahp)-containing cyclic depsipeptides, were isolated from Microcystis aeruginosa NIES-88. The structures were elucidated by analyses of HRFABMS, 1D and 2D NMR spectra, and chemical degradation. Micropeptins 88-N and 88-Y inhibited chymotrypsin. The inhibitory activities were closely related to the amino acid residue that was attached to the amino group of Ahp.

Cyanopeptolin 963A, a chymotrypsin inhibitor of Microcystis PCC 7806

A new depsipeptide, cyanopeptolin 963 A (1), was isolated from an axenic strain of the toxic freshwater cyanobacterium Microcystis PCC 7806. The structure of this compound was elucidated by chemical and spectroscopic analyses, including high-resolution ESI-FTICR-MS, 2-D NMR, and GC-MS of the hydrolysate. The major structural difference compared to previously characterized cyanopeptolins of this strain is the replacement of the basic amino acid in position 3 by L-tyrosine. Compound 1 displayed inhibitory activity against chymotrypsin with an IC50 value of 0.9 microM.

Effects of phosphate and light on growth of and bioactive peptide production by the Cyanobacterium anabaena strain 90 and its anabaenopeptilide mutant

Cyanobacteria synthesize several types of bioactive secondary metabolites. Anabaena strain 90 produces three types of bioactive peptides, microcystins (inhibitors of protein phosphatases 1 and 2A), anabaenopeptilides, and anabaenopeptins (serine protease inhibitors). To investigate the role of the anabaenopeptilides in Anabaena, wild-type strain 90 (WT) and its anabaenopeptilide deficient mutant (MU) were cultured with various light and phosphate levels to evaluate the effects and coeffects of these growth factors on the concentrations of the three classes of peptides and the growth characteristics. WT and MU grew in comparable ways under the different growth conditions. The total peptide concentration in WT was significantly higher than that in MU (2.5 and 1.4 microg/mg [dry weight], respectively). Interestingly, the average concentration of anabaenopeptins was significantly higher in MU than in WT (0.59 and 0.24 microg/mg [dry weight], respectively). The concentration of microcystins was slightly but not statistically significantly higher in MU than in WT (1.0 and 0.86 microg/mg [dry weight], respectively). In WT, the highest peptide concentrations were usually found after 13 days in cultures grown at medium light intensities (23 micromol m(-2) s(-1)) and with the highest phosphate concentrations (2,600 microg liter(-1)). In MU, the highest peptide concentrations were found in 13-day-old cultures grown at medium light intensities (23 micromol m(-2) s(-1)) and with phosphate concentrations greater than 100 microg liter(-1). The higher concentrations of anabaenopeptins in MU may compensate for the absence of anabaenopeptilides. These findings clearly indicate that these compounds may have some linked function in the producer organism, the nature of which remains to be discovered.

Binding structure of elastase inhibitor scyptolin A

Natural bioactive compounds are of general interest to pharmaceutical research because they may be used as leads in drug development campaigns. Among them, scyptolin A and B from Scytonema hofmanni PCC 7110 are known to inhibit porcine pancreatic elastase, which in turn resembles the attractive drug target neutrophil elastase. The crystal structure of scyptolin A as bound to pancreatic elastase was solved at 2.8 A resolution. The inhibitor occupies the most prominent subsites S1 through S4 of the elastase and prevents a hydrolytic attack by covering the active center with its rigid ring structure. The observed binding structure may help to design potent elastase inhibitors.

Hofmannolin, a cyanopeptolin from Scytonema hofmanni PCC 7110

Two depsipeptide metabolites, scyptolin A and B, were reported recently from the axenically grown terrestrial cyanobacterium Scytonema hofmanni PCC 7110. A related, novel depsipeptide was isolated from this Scytonema and designated hofmannolin. The amino acid analysis in context with infrared, mass and 1H/13C-NMR spectroscopies revealed a cyclic depsipeptide structure of M(r) 1073 belonging to the class of cyanopeptolins. Two peculiar features distinguish hofmannolin from other cyanopeptolins: O-methylated tyrosine forms the sixth moiety from the amino terminus, and the N-terminus is blocked by 2-hydroxy-3-methyl-valeric acid, a residue that has not yet been reported as a component in other cyanopeptolins. Preliminary assays of peptidase inhibitory and antimicrobial activities suggested negligible bioactivities for hofmannolin.

Scyptolin A and B, cyclic depsipeptides from axenic cultures of Scytonema hofmanni PCC 7110

Two novel cyclic depsipeptides were isolated from axenic cultures of the terrestrial cyanobacterium Scytonema hofmanni PCC 7110 and designated scyptolin A and B. Amino acid analyses in context with mass and 1H/13C NMR spectroscopies revealed a composition typical for heterologous cyanopeptolins but containing the uncommon residue 3'-chloro-N-methyl-Tyr (cmTyr) and a unique sidechain. Scyptolin A and B both consist of the N-acylated peptide But(1)-Ala(2)-Thr(3)-Thr(4)-Leu(5)-Ahp(6) (3-amino-6-hydroxy-2-oxo-1-piperidine)-Thr(7)-cmTyr(8)-Val(9), which forms a 19-membered ring by esterification of the carboxyl of Val(9) with the hydroxyl of Thr(4). In scyptolin B, the hydroxyl of the Thr(3) residue is additionally esterified with N-butyroyl-Ala. Both scyptolin A and B exhibit selective inhibition of porcine pancreatic elastase in vitro with IC(50) values of 3.1 microg/ml.

Biochemical and pharmacological investigations of selected cyanobacteria

Cyanobacteria are a very old group of prokaryotic organisms that produce a variety of secondary metabolites with antibiotic, algicide, cytotoxic, immunosuppressive and enzyme inhibiting activities. In the last decades structures of pure compounds have been determined as phenols, peptides, alkaloids or terpenoids (Falch, 1996). Screening of lipophilic and hydrophilic extracts from cultured cyanobacteria or waterbloom material, isolated from German lakes and the Baltic sea for antiviral, antibiotic, immunomodulating and enzyme inhibiting activity in different in vitro systems revealed strains with interesting effects. These strains were cultivated in 45 litre photobioreactors to produce enough biomass for bioassay-guided isolation of the active substances. First results characterising active substances are reported.

Genes encoding synthetases of cyclic depsipeptides, anabaenopeptilides, in Anabaena strain 90

Anabaena strain 90 produces three hepatotoxic heptapeptides (microcystins), two seven-residue depsipeptides called anabaenopeptilide 90A and 90B, and three six-residue peptides called anabaenopeptins. The anabaenopeptilides belong to a group of cyanobacterial depsipeptides that share the structure of a six-amino-acid ring with a side-chain. Despite their similarity to known cyclic peptide toxins, no function has been assigned to the anabaenopeptilides. Degenerate oligonucleotide primers based on the conserved amino acid sequences of other peptide synthetases were used to amplify DNA from Anabaena 90, and the resulting polymerase chain reaction (PCR) products were used to identify a peptide synthetase gene cluster. Four genes encoding putative anabaenopeptilide synthetase domains were characterized. Three genes, apdA, apdB and apdD, contain two, four and one module, respectively, encoding a total of seven modules for activation and peptide bond formation of seven L-amino acids. Modules five and six also carry methyltransferase-like domains. Before the first module, there is a region similar in amino acid sequence to formyltransferases. A fourth gene (apdC), between modules six and seven, is similar in sequence to halogenase genes. Thus, the order of domains is co-linear with the positions of amino acid residues in the finished peptide. A mutant of Anabaena 90 was made by inserting a chloramphenicol resistance gene into the apdA gene. DNA amplification by PCR confirmed the insertion. Mass spectrometry analysis showed that anabaenopeptilides are not made in the mutant strain, but other peptides, such as microcystins and anabaenopeptins, are still produced by the mutant.

Co-occurrence of non-toxic (cyanopeptolin) and toxic (microcystin) peptides in a bloom of Microcystis sp. from a Chilean lake

A cyanobacterial bloom occurring in 1998 in lake Tres Pascualas (Concepción/Chile) was found to be dominated by Microcystis sp. The bloom contained both non-toxic (cyanopeptolin-type) and hepatotoxic (microcystin-type) peptides. Cyanopeptolin structure of the non-toxic peptides (called cyanopeptolin VW-1 and VW-2, respectively) was revealed by matrix assisted laser desorption ionization mass spectrometry (MALDI-TOF-MS) of whole cells, showing dominant molecular ions at m/z = 975 and m/z 995, respectively. On post source decay (PSD), both cyanopeptolins showed fragments deriving from Ahp-Phe-MTyr (3-amino-6-hydroxy-2-piperidone), the characteristic partial structure of cyanopeptolins. The amounts of each of the two cyanopeptolins could only roughly be estimated to be >0.1% of bloom material dry weight. In addition the blooms contained microcystins (20 microg/g bloom dry weight as determined by RP-HPLC, 13 microg/g according to ELISA determination). MALDI-TOF-MS revealed several structural variants of microcystin: MCYST-RR (microcystin with Arg and Arg, indicated by m/z 1,038 and confirmed by PSD revealing a m/z = 135 fragment deriving from the Adda side chain, MCYST-FR (microcystin with Phe and Arg, indicated by m/z = 1,015). The presence of [Asp(3)]-MCYST-LR (microcystin with Leu and Arg, Asp non-methylated, indicated by m/z 981), and [Asp(3)]-MCYST-YR (microcystin with Tyr and Arg, Asp non-methylated, indicated by m/z 1,031) were likely. The relative amounts of the peptides varied between February, April, and May. Whole cell extracts from the bloom material revealed specific enzyme inhibitory activities. The serin-proteases trypsin, plasmin, elastase were inhibited, assumable due to the cyanopeptolins found. Elastase and the cysteine-protease papain were not inhibited, inhibitions of protein kinase and glutathione S-transferase (GST) were low. Strong inhibition was observed with protein-phosphatase-1, likely due to the microcystins present in the samples.

Role of microcystins in poisoning and food ingestion inhibition of Daphnia galeata caused by the cyanobacterium Microcystis aeruginosa

The effects of microcystins on Daphnia galeata, a typical filter-feeding grazer in eutrophic lakes, were investigated. To do this, the microcystin-producing wild-type strain Microcystis aeruginosa PCC7806 was compared with a mcy- PCC7806 mutant, which could not synthesize any variant of microcystin due to mutation of a microcystin synthetase gene. The wild-type strain was found to be poisonous to D. galeata, whereas the mcy- mutant did not have any lethal effect on the animals. Both variants of PCC7806 were able to reduce the Daphnia ingestion rate. Our results suggest that microcystins are the most likely cause of the daphnid poisoning observed when wild-type strain PCC7806 is fed to the animals, but these toxins are not responsible for inhibition of the ingestion process.

Rapid identification of the new anabaenopeptin G from Planktothrix agardhii HUB 011 using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Toxic water blooms from cyanobacteria in lakes and rivers are a worldwide phenomenon. A new technique is presented for the rapid detection of toxic and nontoxic blooms. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was employed to identify mainly peptide metabolites (microcystins, anabaenopeptins, cyanopeptolins, microviridins, microginins and aeruginosins) from microgram quantities of prepared cells within minutes. The spectra show the presence of peptides in strains or water blooms simultaneously. A new compound has been identified using the post source decay (PSD) and collision induced dissociation (CID) mode. This new compound has been defined as anabaenoeptin G. The potential of the method for screening of various secondary metabolite producers for defined products including antibiotics is discussed.