Isolation and Total Synthesis of PM170453, a New Cyclic Depsipeptide Isolated from Lyngbya sp.

In our continuing search for biologically active new chemical entities from marine organisms, we have isolated a new cyclic depsipeptide, PM170453 (1), from a cyanobacterium of the genus Lyngbya sp., collected in the Indo-Pacific Ocean. Structure elucidation of the isolated compound was determined by spectroscopic methods including MS, 1H, 13C and 2D-NMR. To solve the supply problem for 1 and progress pharmaceutical development, the total synthesis of 1 that involves a total of 20 chemical steps in a convergent process was carried out. Its in vitro cytotoxic activity against four human tumor cell lines, as well as the inhibition of the interaction between the programmed cell death protein 1 PD-1 and its ligand PD-L1 were also evaluated.

Biosynthesis and characterisations of silver nanoparticles with filamentous cyanobacterium Lyngbya sp. with in vitro antibacterial properties against MDR pathogenic bacteria.

This study describes phycocompounds of the non-N2-fixing filamentous cyanobacterium Lyngbya sp., which has potential bio-reducing and stabilizing heavy metal-accumulating properties for synthesizing silver nanoparticles (AgNPs), whose formation was confirmed by the colour change of the Lyngbya sp.-AgNP solution from pale green to deep brown. The reduction of 'Lyngbya sp.-AgNPs', called Lsp-AgNPs, was proved by UV-visible photo-spectrometry analysis with an obtained peak value at 426 nm. Lsp-AgNPs were characterised by analytical techniques, XRD, FESEM, DLS and FTIR. The XRD analysis with 5-70 theta was obtained at 2Ï´ angles ranging from 38.79º with intensity, indicating the crystal structure of Lsp-AgNPs. The FESEM analysis indicated the area size at 20-50 µm; in the DLS analysis, the peak at 400 d nm indicated the size and distribution of Lsp-AgNPs. In FTIR analysis, the peaks were obtained at wavenumbers 3338, 1639, and 542 cm-1, which indicated the presence of N-H, -OH and C=O functional groups in Lsp-AgNPs. Those had in vitro antibacterial activities against Gram-negative Escherichia coli (MTCC 443) and Pseudomonas aeruginosa (MTCC 1688) and Gram-positive Staphylococcus aureus (MTCC 7443) bacterial strains with zone of inhibitions (ZOI) of 16, 12 and 14 mm, respectively, with comparing the antibiotic gentamycin as a positive control, as was monitored with agar-well diffusion method. Furthermore, the MIC value was 50 mg/ml, and MBC values of 65 mg/ml of Lsp-AgNPs were effective against those bacteria. Thus, Lsp-AgNPs had potential antibacterial activities against MDR pathogenic S. aureus, E. coli and P. aeruginosa. In conclusion, MDR pathogenic bacteria could be controlled as prodrugs in the future.

Assessment and identification of bioactive metabolites from terrestrial Lyngbya spp. responsible for antioxidant, antifungal, and anticancer activities.

Lyngbya from fresh and marine water produces an array of pharmaceutically bioactive therapeutic compounds. However, Lyngbya from agricultural soil is still poorly investigated. Hence, in this study, the bioactive potential of different Lyngbya spp. extract was explored. Intracellular petroleum ether extract of L. hieronymusii K81 showed the highest phenolic content (626.22 ± 0.65 µg GAEs g-1 FW), while intracellular ethyl acetate extract of L. aestuarii K97 (74.02 ± 0.002 mg QEs g-1 FW) showed highest flavonoid content. Highest free radical scavenging activity in terms of ABTS•+ was recorded in intracellular methanolic extract of Lyngbya sp. K5 (97.85 ± 0.068%), followed by L. wollei K80 (97.22 ± 0.059%) while highest DPPH• radical scavenging activity observed by intracellular acetone extract of Lyngbya sp. K5 (54.59 ± 0.165%). All the extracts also showed variable degrees of antifungal activities against Fusarium udum, F. oxysporum ciceris, Colletotrichum capsici, and Rhizoctonia solani. Further, extract of L. wollei K80 and L. aestuarii K97 showed potential anticancer activities against MCF7 (breast cancer) cell lines. GC-MS analyses of intracellular methanolic extract of L. wollei K80 showed the dominance of PUFAs with 9,12,15-octadecatrienoic acid, methyl ester, (Z,Z,Z) as the most abundant bioactive compound. On the other hand, the extracellular ethyl acetate extract of L. aestuarii K97 was rich in alkanes and alkenes with 1-hexyl-2-nitrocyclohexane as the most predominant compound. Extracts of Lyngbya spp. rich in novel secondary metabolites such as PUFAs, alkanes, and alkenes can be further explored as an alternative and low-cost antioxidant and potential apoptogens for cancer therapy.

Recent progression on phytochemicals and pharmacological properties of the filamentous cyanobacterium Lyngbya sp.

The distribution and phytochemistry of the non-nitrogen fixing, filamentous cyanobacterium (blue-green alga) Lyngbya sp., and the inherent antimicrobial and anticancer activities of its phycochemicals as well as of the biosynthesized nanoparticles as their pharmaceutical potencies are considered. Several phycocompounds of curio, apramide, apratoxin, benderamide, cocosamides, deoxymajusculamide, flavonoids, lagunamides, lipids, proteins, amino acids, lyngbyabellin, lyngbyastatin, majusculamide, peptides, etc. were isolated from Lyngbya sp., which had a lot of potential pharmaceutical activities; those compounds had antibacterial, antiviral, antifungal, anticancer, antioxidant, anti-inflammatory, ultraviolet protectant, and other activities. Particularly, several Lyngbya phycocompounds had potent antimicrobial potencies, seen through in vitro controlling of several frequently encountered multidrug-resistant (MDR) clinically belligerent strains of pathogenic bacteria isolated from clinical samples. The aqueous extracts of Lyngbya sp. were used for the synthesis of silver and copper oxide nanoparticles, which were used in pharmacological trials too. The nanoparticles biosynthesized with Lyngbya sp. had several uses such as biofuel, agro-based applications, in cosmetics, and industrial uses as biopolymers, and being potent antimicrobial and anticancer agents and in drug-delivery too, as medical applications. It could be concluded that the Lyngbya phycochemicals and the biosynthesized nanoparticles have future uses as antimicrobial namely as bacterial and fungal and anti-cancer agents, with promising medical and industrial uses.

Algae impacted drinking water: Does switching to chloramination produce safer drinking water?

Harmful algal (cyanobacterial) blooms (HABs) are increasing throughout the world. HABs can be a direct source of toxins in freshwater sources, and associated algal organic matter (AOM) can act as precursors for the formation of disinfection by-products (DBPs) in drinking water. This study investigated the impacts of algae on DBP formation using treatment with chloramine, which has become a popular disinfectant in the U.S. and in several other countries because it can significantly lower the levels of regulated DBPs formed. Controlled laboratory chloraminations were conducted using live field-collected algal biomass dominated by either Phormidium sp. or Microseira wollei (formerly known as Lyngbya wollei) collected from Lake Wateree and Lake Marion, SC. Sixty-six priority, unregulated or regulated DBPs were quantified using gas chromatography (GC)-mass spectrometry (MS). The presence of HAB-dominated microbial communities in source waters led to significant increases in more toxic nitrogen-containing DBPs (1.5-5 fold) relative to lake waters collected in HAB-free waters. Compared to chlorinated Phormidium-impacted waters, chloraminated waters yielded lower total DBP levels (up to 123 µg/L vs. 586 µg/L for low Br-/I- waters), but produced a greater number of brominated, iodinated, and mixed halogenated DBPs in high Br-/I- waters. Among the DBPs formed in Phormidium-impacted chloraminated waters, dichloroacetic acid, trichloromethane, chloroacetic acid, chloropropanone, and dichloroacetamide were dominant. For Microseira wollei-impacted chloraminated waters, total DBP concentrations ranged from 33 to 145 µg/L (approximately 3-5 times lower than chlorination), with dichloroacetic acid, dichloroacetamide, and trichloromethane dominant. Overall, chloramination significantly reduced calculated cytotoxicity and genotoxicity in low Br- and I- waters, but produced 1.3 fold higher calculated cytotoxicity (compared to chlorine) with high Br-/I- waters due to increased formation of more toxic iodo- and mixed halogenated DBPs.

Structure Elucidation of Two Intriguing Neo-Debromoaplysiatoxin Derivatives from Marine Cyanobacterium Lyngbya sp. Showing Strong Inhibition of Kv1.5 Potassium Channel and Differential Cytotoxicity.

Two aplysiatoxin derivatives, neo-debromoaplysiatoxin I (1) and neo-debromoaplysiatoxin J (2), were isolated from marine cyanobacterium Lyngbya sp. collected from the South China Sea. Their structures including absolute configurations were assigned by spectroscopic analysis, in combination with GIAO NMR shift calculation and DP4+ analysis. Structures of neo-debromoaplysiatoxin I and neo-debromoaplysiatoxin J contained a decahydro-5H-pyrano [2,3,4-de] chromen-5-one 6/6/6 ring skeleton and an intriguing peroxide bridge group, respectively, which are unprecedented structure scaffold and motif in aplysiatoxins. Two compounds displayed comparable inhibitory activities against Kv1.5 K+ channel with IC50 values of 2.59 ± 0.37 µM (1) and 1.64 ± 0.15 µM (2); however, they presented differential cytotoxic effects. It is worth noting that neo-debromoaplysiatoxin J, containing a peroxide bridge, showed remarkable cytotoxicity against four cancer cell lines including SW480, SGC7901, LoVo and PC-9 compared to the human normal cell line.

Anti-Infective Secondary Metabolites of the Marine Cyanobacterium Lyngbya Morphotype between 1979 and 2022.

Cyanobacteria ascribed to the genus Lyngbya (Family Oscillatoriaceae) represent a potential therapeutic gold mine of chemically and biologically diverse natural products that exhibit a wide array of biological properties. Phylogenetic analyses have established the Lyngbya 'morpho-type' as a highly polyphyletic group and have resulted in taxonomic revision and description of an additional six new cyanobacterial genera in the same family to date. Among the most prolific marine cyanobacterial producers of biologically active compounds are the species Moorena producens (previously L. majuscula, then Moorea producens), M. bouillonii (previously L. bouillonii), and L. confervoides. Over the years, compounding evidence from in vitro and in vivo studies in support of the significant pharmaceutical potential of 'Lyngbya'-derived natural products has made the Lyngbya morphotype a significant target for biomedical research and novel drug leads development. This comprehensive review covers compounds with reported anti-infective activities through 2022 from the Lyngbya morphotype, including new genera arising from recent phylogenetic re-classification. So far, 72 anti-infective secondary metabolites have been isolated from various Dapis, Lyngbya, Moorea, and Okeania species. These compounds showed significant antibacterial, antiparasitic, antifungal, antiviral and molluscicidal effects. Herein, a comprehensive literature review covering the natural source, chemical structure, and biological/pharmacological properties will be presented.

Growth of the harmful benthic cyanobacterium Microseira wollei is driven by legacy sedimentary phosphorous.

Models for cyanobacterial harmful algae blooms (cHABs) in fresh waters are usually predicated on the relationship between cyanobacterial ecology and dissolved nutrients, particularly phosphorous. Here we show legacy sediment-associated phosphorous as the primary driver of a benthic cHAB, not phosphorous in the water column. Biogeographical surveys by teams of citizen science volunteers working with the University of South Carolina identified over 200 distinct mats of Microseira wollei in Lake Wateree, SC based on toxin characterization. In sum these were estimated to affect approximately 175 km of the lake's shoreline. This growth occurred under water quality conditions that were near or below the regulatory total maximum daily load for phosphorous and nitrogen. A series of established predictive models for cyanobacterial biomass growth were applied retroactively to match the measured growth with measured water quality parameters. The only component of the system that successfully predicted microbial biomass was sedimentary phosphorous. Concentrations of the Lyngbya wollei toxins (LWTs) 1, 4, 5, and 6 were determined at multiple sites over an 18-month period and a toxin inventory for the lake was calculated. Toxin profiles between sites differed at the 95% level of confidence, establishing each site as a unique mat. An empirical model of toxin production potential based on sedimentary phosphorous was developed.

Morpho-anatomical characters of family Oscillatoriaceae (algae) identified using primitive (LM) and advance technique (SEM) from Punjab, Pakistan.

In this study, 34 species belonging to the class Nostocophyceae order Nostocales and family Oscillatoriaceae were identified based on light microscopy (LM) and scanning electron microscopy (SEM). All species belong to nine genera of which two species belong to Arthrospira, six species to Lyngbya, ten species belongs to Oscillatoria, six species belong to Spirulina, seven species to Phormidium, three species to Microcoleus. The morpho-anatomical characters were identified among different species using LM and SEM. These studies highlighted that north-eastern area of Punjab was blessed with the diversity of algae. These outcomes also indicated that for internal examination along with LM, SEM was necessary for correct identification of algal sample up to specie level. RESEARCH HIGHLIGHTS: The different Oscillatoria species abundance in waste-water of four different areas. The sampling was carried out randomly in different seasons from the water bodies especially from waste-water. The morpho-anatomical characters were recognized using light microscopy (LM) and scanning electron microscopy (SEM). Thirty-four species belonging to the class Nostocophyceae order Nostocales and family Oscillatoriaceae were identified based on LM and SEM.

Microseira wollei and Phormidium algae more than doubles DBP concentrations and calculated toxicity in drinking water.

Warm weather and excess nutrients from agricultural runoff trigger harmful algal blooms, which can affect drinking water safety due to the presence of algal toxins and the formation of disinfection by-products (DBPs) during drinking water treatment. In this study, 66 priority, unregulated and regulated DBPs were quantified in chlorinated controlled laboratory reactions of harmful algae Microseira wollei (formerly known as Lyngbya wollei) and Phormidium using gas chromatography (GC)-mass spectrometry (MS). Live algae samples collected from algae-impacted lakes in South Carolina were chlorinated in both ultrapure water and real source waters containing natural organic matter. DBPs were also measured in finished water from a real drinking water plant impacted by a Microseira bloom. Results show that the presence of Microseira and Phormidium more than doubles total concentrations of DBPs formed by chlorination, with levels up to 586 µg/L formed in natural lake waters. Toxic nitrogen-containing DBPs also more than doubled in concentration, with levels up to 36.1, 3.6, and 37.9 µg/L for haloacetamides, halonitromethanes, and haloacetonitriles, respectively. In ultrapure water, DBPs also formed up to 314 µg/L when algae was chlorinated, demonstrating their ability to serve as direct precursors for these DBPs. When environmentally relevant levels of bromide and iodide were added to chlorination reactions, total DBPs increased 144, 51, and 24% for drinking water reservoir, Lake Marion and Lake Wateree Microseira respectively and 29% for Phormidium. Iodo-DBPs, bromochloroiodomethane, chloroiodoacetic acid, bromoiodoacetic acid, and diiodoacetic acid were observed in finished water from a drinking water plant impacted by Microseira, and bromochloroiodomethane and dibromoiodomethane were observed in chlorinated ultrapure water containing algae, bromide, and iodide. Notably, total calculated cytotoxicity tripled in Microseira-impacted waters and doubled for Phormidium-impacted waters. Calculated genotoxicity doubled for Microseira-impacted waters and more than doubled in Phormidium-impacted waters. Haloacetonitriles were major drivers of calculated cytotoxicity in algae-impacted waters, while haloacetic acids were major drivers of calculated genotoxicity in algae-impacted waters. These results provide the most extensive assessment of DBPs formed from chlorination of algae-impacted waters and highlight potential impacts to drinking water and human health. Results from this study are particularly applicable to drinking water treatment plants that employ pre-chlorination, which can cause the release of algal organic matter (AOM) precursors to form DBPs.

Metagenomics Analysis to Investigate the Microbial Communities and Their Functional Profile During Cyanobacterial Blooms in Lake Varese.

Toxic cyanobacterial blooms represent a natural phenomenon caused by a mass proliferation of photosynthetic prokaryotic microorganisms in water environments. Bloom events have been increasingly reported worldwide and their occurrence can pose serious threats to aquatic organisms and human health. In this study, we assessed the microbial composition, with a focus on Cyanobacteria, in Lake Varese, a eutrophic lake located in northern Italy. Water samples were collected and used for obtaining a 16S-based taxonomic profile and performing a shotgun sequencing analysis. The phyla found to exhibit the greatest relative abundance in the lake included Proteobacteria, Cyanobacteria, Actinobacteriota and Bacteroidota. In the epilimnion and at 2.5 × Secchi depth, Cyanobacteria were found to be more abundant compared to the low levels detected at greater depths. The blooms appear to be dominated mainly by the species Lyngbya robusta, and a specific functional profile was identified, suggesting that distinct metabolic processes characterized the bacterial population along the water column. Finally, analysis of the shotgun data also indicated the presence of a large and diverse phage population.

Identification of apparently neurotoxic metabolites from assemblages of marine filamentous cyanobacteria associated with the intoxication of captive bottlenose dolphins (Tursiops truncatus) in the Florida Keys.

Intoxications of captive bottlenose dolphins (Tursiops truncatus) in the Florida Keys have been linked to observed interactions with marine macrophytic algal and cyanobacterial communities within enclosures. Taxonomic characterization of these communities coupled, in turn, to available observational data collected during intoxication events point to a contribution of filamentous cyanobacterial assemblages comprised of members of the polyphyletic genus, Lyngbya sensu lato. To identify toxic metabolites possibly relevant to these intoxications, chemical screening for known neurotoxins from cyanobacteria, as well as other regionally relevant harmful algal bloom (HAB) taxa, was combined with toxicity testing, and subsequent bioassay-guided fractionation, employing early life stages (i.e., embryos and larvae) of zebrafish (Danio rerio) as a well-established aquatic vertebrate toxicological model. Chemical analyses did not detect (within analytical limits) any of the known algal or cyanobacterial neurotoxins. Toxicity testing, alongside bioassay-guided fractionation, however, identified several chemical fractions with a range of potentially relevant bioactivities in both zebrafish embryos and post-hatch larvae including, in particular, behavioral (e.g., aberrant swimming) and physiological (e.g., altered heart rate) endpoints indicative of possible neurotoxicity, and subsequent chemical characterization of fractions suggested a contribution of the previously identified bioactive metabolite, eudesmacarbonate, in the observed toxicity. Comparative toxicological assessment with PbTx-2, as a positive control for neurotoxicity in the zebrafish model, further supported neurotoxic activity of cyanobacterial metabolites potentially relevant, in turn, to a contribution of these metabolites to dolphin intoxications. These findings suggest, in general, that marine zoological facilities may be affected by regional HABs, and assessments of potentially toxigenic algae and cyanobacteria should be included in management strategies in these facilities.

Photochemical changes during rehydration of an intertidal cyanobacterial mat exposed to variations in salinity and light intensity.

This study focuses on a Lyngbya cf. aestuarii dominated mat community from the intertidal zone of the Laguna Ojo de Liebre, Baja California Sur. In this environment, the mat is desiccated for several days between spring tides. While the mats were desiccated, photosynthetic activity was absent but recovered rapidly (~3 h) upon rehydration. It has been shown previously that the rate of photosynthetic recovery is dependent on both light intensity and salinity. In the current study, photosynthetic recovery was measured based on chlorophyll a fluorescence using pulse amplitude modulated (PAM) fluorometry. Upon the addition of water, photosystem II (PSII) complexes recovered the capacity for reaction centre excitation. However, these functional centres were initially closed. Respiratory activity early in recovery probably reduced the plastoquinone pool through the shared use of part of the photosynthetic transport chain, thus temporarily blocking electron transport downstream of PSII. The time that PSII complexes remained closed increased with light intensities above saturation. This condition is potentially damaging to the cyanobacteria since the exposure of closed PSII centres to high light intensities can lead to the production of singlet oxygen. After this initial lag period, PSII centres opened rapidly indicating an increase in the flow of electrons from PSII to PSI. The rate of photosynthetic recovery appeared to be limited primarily by the relatively slow return of functional PSII. Photosynthetic recovery rates were slower in salinities greater than those that naturally occur in the intertidal zone.

Effects of a non-native cyanobacterium on bay scallops (Argopecten irradians) in a New England seagrass ecosystem.

Bay scallops (Argopecten irradians) are an economically valuable species whose populations have declined in recent decades due in part to harmful algal and cyanobacterial blooms. Nantucket, Massachusetts hosts one of the last remaining bay scallop fisheries in the U.S., but recently documented the occurrence of a non-native cyanobacterium (Hydrocoleum sp.). Hydrocoleum can form dense mats in seagrass beds, the primary habitat of scallops, but is also diazotrophic, potentially augmenting bioavailable nitrogen to primary producers and fueling secondary production. We conducted surveys to explore the relationships between Hydrocoleum and scallop condition, reproductive potential, and density in eelgrass beds in Nantucket Harbor as well as effects of other habitat characteristics (e.g., eelgrass cover) on these same scallop traits. We found low Hydrocoleum cover during our sampling, but found fewer large scallops in plots with Hydrocoleum, suggesting that this size class may be especially vulnerable to negative effects of Hydrocoleum. Contrary to expectation, we found a positive correlation between Hydrocoleum cover and scallop condition. These patterns suggest that Hydrocoleum may enhance scallop condition, but also affect habitat use, highlighting the need for manipulative experiments to clarify mechanisms driving these relationships. Understanding how non-native species such as Hydrocoleum impact fishery species will help advance conservation and resource management efforts.

Sea lice Lepeophtheirus spinifer, Tuxophorus sp. and Caligus sp. infections on wild-caught queenfish Scomberoides commersonnianus from northern Australia.

Studies of ectoparasites of wild-caught queenfish Scomberoides commersonnianus from several areas in northern Australia were reviewed to investigate relationships between parasite burdens, environmental conditions and external lesions. A sample of 27 queenfish captured near a dredge spoil disposal site in Gladstone Harbour, Queensland, Australia, in January 2012 was anomalous, with a high percentage of fish (66.6%) exhibiting grossly visible skin lesions including foci of erythema and petechial haemorrhages, particularly on the pectoral girdle and ventrolateral surfaces. Microscopically, lesions comprised acute epidermal erosion, ulceration and/or perivascular dermatitis with dermal oedema and depigmentation. Skin lesions were associated with high prevalence (100%) and intensity (mean = 21.2 copepods fish-1, range 4-46) of infection by sea lice Lepeophtheirus spinifer. Only queenfish infected with >10 L. spinifer presented with skin lesions. This is the first record of L. spinifer from Australia. In contrast, grossly visible skin lesions were not reported from queenfish (n = 152) sampled from other sites in the Northern Territory and Queensland, where the sampled fish had a much lower prevalence (51.3%) and intensity (mean = 3.54, range 0-26) of copepod (L. spinifer, Caligus spp. and Tuxophorus sp.) infections. Copepods from queenfish in studies undertaken outside Gladstone Harbour exhibited an over-dispersed pattern of infection, with the vast majority (n = 137, or 90.1%) of fish infected with <5 copepods. These data demonstrate that heavy L. spinifer infections, combined with poor water quality and/or direct exposure to contaminated dredge spoil and blooms of the cyanobacterium Lyngbya majuscula, can be associated with cutaneous disease in wild-caught queenfish.

The occurrence of Affixifilum gen. nov. and Neolyngbya (Oscillatoriaceae) in South Florida (USA), with the description of A. floridanum sp. nov. and N. biscaynensis sp. nov.

South Florida (USA) has a subtropical to tropical climate with an extensive and diverse coastline that supports the growth of benthic cyanobacterial mats (BCMs). These BCMs are widespread and potentially house numerous bioactive compounds; however, the extent of the cyanobacterial diversity within these mats remains largely unknown. To elucidate this diversity, BCMs from select locations in South Florida were sampled and isolated into unicyanobacterial cultures for morphological and molecular studies. Phylogenetic relationships of isolated taxa were assessed using the markers 16S rRNA and 16S-23S rRNA ITS by both maximum likelihood and Bayesian inference. We propose Affixifilum gen. nov. based on morphological characteristics and the 16S rRNA phylogeny. Two species are included: Affixifilum granulosum comb nov. (=Neolyngbya granulosa) found in Brazil and Florida (USA) and A. floridanum sp. nov. Several other features, including pair-wise distance of 16S rRNA and 16S-23S rRNA ITS, 16S-23S rRNA ITS secondary structure, morphology, and ecology, provide support for Affixifilum. We also propose the transfer of Lyngbya regalis to Neolyngbya as N. regalis comb. nov. and include the description of one novel species, N. biscaynensis sp. nov.

Chemical and Biological Study of Novel Aplysiatoxin Derivatives from the Marine Cyanobacterium Lyngbya sp.

Since 1970s, aplysiatoxins (ATXs), a class of biologically active dermatoxins, were identified from the marine mollusk Stylocheilus longicauda, whilst further research indicated that ATXs were originally metabolized by cyanobacteria. So far, there have been 45 aplysiatoxin derivatives discovered from marine cyanobacteria with various geographies. Recently, we isolated two neo-debromoaplysiatoxins, neo-debromoaplysiatoxin G (1) and neo-debromoaplysiatoxin H (2) from the cyanobacterium Lyngbya sp. collected from the South China Sea. The freeze-dried cyanobacterium was extracted with liquid-liquid extraction of organic solvents, and then was subjected to multiple chromatographies to yield neo-debromoaplysiatoxin G (1) (3.6 mg) and neo-debromoaplysiatoxin H (2) (4.3 mg). They were elucidated with spectroscopic methods. Moreover, the brine shrimp toxicity of the aplysiatoxin derivatives representing differential structural classifications indicated that the debromoaplysiatoxin was the most toxic compound (half inhibitory concentration (IC50) value = 0.34 ± 0.036 µM). While neo-aplysiatoxins (neo-ATXs) did not exhibit apparent brine shrimp toxicity, but showed potent blocking action against potassium channel Kv1.5, likewise, compounds 1 and 2 with IC50 values of 1.79 ± 0.22 µM and 1.46 ± 0.14 µM, respectively. Therefore, much of the current knowledge suggests the ATXs with different structure modifications may modulate multiple cellular signaling processes in animal systems leading to the harmful effects on public health.

Cyanotoxin release from the benthic, mat-forming cyanobacterium Microseira (Lyngbya) wollei in the St. Lawrence River, Canada.

Benthic cyanobacterial mats occurring in the St. Lawrence River fluvial lakes Saint-Louis and Saint-Pierre are dominated by Microseira (Lyngbya) wollei which produce several cyanotoxins including LWTX-1 that is characteristic of Microseira wollei. This cyanotoxin is not only present in the filaments forming benthic mats, but was also measured in the water overlying the mats. LWTX-1 was found in all cyanobacterial filament samples (75.29-103.26 ng mg-1) and all overlying water samples (3.01-11.03 ng L-1). Toxin concentrations measured in overlying water and dry biomass were strongly correlated (r = 0.94). Furthermore, LWTX-1 concentration in water was positively correlated with the dissolved organic carbon in water (r = 0.74) and % nitrogen content in cyanobacterial filaments (r = 0.52). A preliminary study was conducted to determine the release and degradation rates of LWTX-1 from a M. wollei mat kept under laboratory conditions over a 3-month period. Toxin measurements revealed an early, massive toxin release followed by a typical decaying function, with a half-life in the order of 17 days. Our results raise concerns about the occurrence and downstream advection of dissolved cyanotoxins from Microseira mats in the aquatic environment. Graphical abstract.

Neo-debromoaplysiatoxin C, with new structural rearrangement, derived from debromoaplysiatoxin.

Neo-debromoaplysiatoxin C (1), a new member of the aplysiatoxin family, was isolated from the marine cyanobacterium Lyngbya sp. The structure of 1 was elucidated based on spectroscopic data, and its stereochemistry was determined from NOESY spectrum and biosynthetic considerations. This new compound presents an intriguing 10-membered lactone ring skeleton derived from debromoaplysiatoxin by structural rearrangement, which is the first example in the aplysiatoxin family. Its biological properties were evaluated for cytotoxicity, PKCδ activation and inhibitory effects on potassium channel.