MS/MS-Based Molecular Networking Approach for the Detection of Aplysiatoxin-Related Compounds in Environmental Marine Cyanobacteria

Certain strains of cyanobacteria produce a wide array of cyanotoxins, such as microcystins, lyngbyatoxins and aplysiatoxins, that are associated with public health issues. In this pilot study, an approach combining LC-MS/MS and molecular networking was employed as a rapid analytical method to detect aplysiatoxins present in four environmental marine cyanobacterial samples collected from intertidal areas in Singapore. Based on 16S-ITS rRNA gene sequences, these filamentous cyanobacterial samples collected from Pulau Hantu were determined as Trichodesmium erythraeum, Oscillatoria sp. PAB-2 and Okeania sp. PNG05-4. Organic extracts were prepared and analyzed on LC-HRMS/MS and Global Natural Product Social Molecular Networking (GNPS) for the presence of aplysiatoxin-related molecules. From the molecular networking, six known compounds, debromoaplysiatoxin (1), anhydrodebromoaplysiatoxin (2), 3-methoxydebromoaplysiatoxin (3), aplysiatoxin (4), oscillatoxin A (5) and 31-noroscillatoxin B (6), as well as potential new analogues, were detected in these samples. In addition, differences and similarities in molecular networking clusters related to the aplysiatoxin molecular family were observed in extracts of Trichodesmium erythraeum collected from two different locations and from different cyanobacterial species found at Pulau Hantu, respectively.

Geosmin production and polyphasic characterization of Oscillatoria limosa Agardh ex Gomont isolated from the open canal of a large drinking water system in Tianjin City, China

Taste and odor (T & O) episodes always cause strong effects on drinking water supply system. Luanhe River diversion into Tianjin City in China is an important drinking water resource. Massive growth of a benthic filamentous cyanobacterium with geosmin production in the open canal caused a strong earthy odor episode in Tianjin. On the basis of the morphological and molecular identification of this cyanobacterium as Oscillatoria limosa Agardh ex Gomont, the genetic basis for geosmin biosynthesis and factors influencing growth and geosmin production of O. limosa CHAB 7000 were studied in this work. A 2268-bp open reading frame, encoding 755 amino acids, was amplified and characterized as the geosmin synthase gene (geo), followed by a cyclic nucleotide-binding protein gene (cnb). Phylogenetic analysis implied that the evolution of the geosmin genes in O. limosa CHAB 7000 might involve a horizontal gene transfer event. Examination on the growth and geosmin production of O. limosa CHAB 7000 at different light intensities showed that the maximum geosmin production was observed at 10μmol photons m^-2s^-1, while the optimum growth was at 60μmol photons m^-2s^-1. Under three temperature conditions (15°C, 25°C, and 35°C), the maximum growth and geosmin production were observed at 25°C. Most amounts of geosmin were retained in cells during the growth phase, but high temperature and low light intensity increased the release of geosmin into the medium, implying that O. limosa CHAB 7000 had a high potential harm for the release of geosmin from its cells at these adverse conditions.

Molecular cloning and expression analysis of a new bilin lyase: the cpcT gene encoding a bilin lyase responsible for attachment of phycocyanobilin to Cys-153 on the β-subunit of phycocyanin in Arthrospira platensis FACHB314

To study the assembly of phycocyanin β subunit, the gene cpcT was first cloned from Arthrospira platensis FACHB314. To explore the function of cpcT, the DNA of phycocyanin β subunit and cpcT were transformed into Escherichia coli BL21 with the plasmid pET-hox1-pcyA, which contained the genes hemeoxygenase 1 (Hox1) and ferredoxin oxidoreductase (PcyA) needed to produce phycocyanobilin. The transformed strains showed specific phycocyanin fluorescence, and the fluorescence intensity was stronger than the strains with only phycocyanin β subunit, indicating that CpcT can promote the assembly of phycocyanin to generate fluorescence. To study the possible binding sites of apo-phycocyanin and phycocyanobilin, the Cys-82 and Cys-153 of the β subunit were individually mutated, giving two kinds of mutants. The results show that Cys-153 maybe the active site for β subunit binding to phycocyanobilins, which is catalyzed by CpcT in A. platensis FACHB314.

Characterisation of the bacterial and fungal communities associated with different lesion sizes of dark spot syndrome occurring in the coral Stephanocoenia intersepta

The number and prevalence of coral diseases/syndromes are increasing worldwide. Dark Spot Syndrome (DSS) afflicts numerous coral species and is widespread throughout the Caribbean, yet there are no known causal agents. In this study we aimed to characterise the microbial communities (bacteria and fungi) associated with DSS lesions affecting the coral Stephanocoenia intersepta using nonculture molecular techniques. Bacterial diversity of healthy tissues (H), those in advance of the lesion interface (apparently healthy AH), and three sizes of disease lesions (small, medium, and large) varied significantly (ANOSIM R  = 0.052 p<0.001), apart from the medium and large lesions, which were similar in their community profile. Four bacteria fitted into the pattern expected from potential pathogens; namely absent from H, increasing in abundance within AH, and dominant in the lesions themselves. These included ribotypes related to Corynebacterium (KC190237), Acinetobacter (KC190251), Parvularculaceae (KC19027), and Oscillatoria (KC190271). Furthermore, two Vibrio species, a genus including many proposed coral pathogens, dominated the disease lesion and were absent from H and AH tissues, making them candidates as potential pathogens for DSS. In contrast, other members of bacteria from the same genus, such as V. harveyii were present throughout all sample types, supporting previous studies where potential coral pathogens exist in healthy tissues. Fungal diversity varied significantly as well, however the main difference between diseased and healthy tissues was the dominance of one ribotype, closely related to the plant pathogen, Rhytisma acerinum, a known causal agent of tar spot on tree leaves. As the corals’ symbiotic algae have been shown to turn to a darker pigmented state in DSS (giving rise to the syndromes name), the two most likely pathogens are R. acerinum and the bacterium Oscillatoria, which has been identified as the causal agent of the colouration in Black Band Disease, another widespread coral disease.

Phylogeny-guided isolation of ethyl tumonoate A from the marine cyanobacterium cf. Oscillatoria margaritifera

The evolutionary relationships of cyanobacteria, as inferred by their SSU (16S) rRNA genes, were used as predictors of their potential to produce varied secondary metabolites. The evolutionary relatedness in geographically distant cyanobacterial specimens was then used as a guide for the detection and isolation of new variations of predicted molecules. This phylogeny-guided isolation approach for new secondary metabolites was tested in its capacity to direct the search for specific classes of new natural products from Curaçao marine cyanobacteria. As a result, we discovered ethyl tumonoate A (1), a new tumonoic acid derivative with anti-inflammatory activity and inhibitory activity of calcium oscillations in neocortical neurons.

A putative gene cluster from a Lyngbya wollei bloom that encodes paralytic shellfish toxin biosynthesis

Saxitoxin and its analogs cause the paralytic shellfish-poisoning syndrome, adversely affecting human health and coastal shellfish industries worldwide. Here we report the isolation, sequencing, annotation, and predicted pathway of the saxitoxin biosynthetic gene cluster in the cyanobacterium Lyngbya wollei. The gene cluster spans 36 kb and encodes enzymes for the biosynthesis and export of the toxins. The Lyngbya wollei saxitoxin gene cluster differs from previously identified saxitoxin clusters as it contains genes that are unique to this cluster, whereby the carbamoyltransferase is truncated and replaced by an acyltransferase, explaining the unique toxin profile presented by Lyngbya wollei. These findings will enable the creation of toxin probes, for water monitoring purposes, as well as proof-of-concept for the combinatorial biosynthesis of these natural occurring alkaloids for the production of novel, biologically active compounds.

Biosynthesis of cylindrospermopsin and 7-epicylindrospermopsin in Oscillatoria sp. strain PCC 6506: identification of the cyr gene cluster and toxin analysis

Cylindrospermopsin is a cytotoxin produced by Cylindrospermopsis raciborskii and other cyanobacteria that has been implicated in human intoxications. We report here the complete sequence of the gene cluster responsible for the biosynthesis of this toxin in Oscillatoria sp. strain PCC 6506. This cluster of genes was found to be homologous with that of C. raciborskii but with a different gene organization. Using an enzyme-linked immunosorbent assay and an optimized liquid chromatography analytical method coupled to tandem mass spectrometry, we detected 7-epicylindrospermopsin, cylindrospermopsin, and 7-deoxycylindrospermopsin in the culture medium of axenic Oscillatoria PCC 6506 at the following relative concentrations: 68.6%, 30.2%, and 1.2%, respectively. We measured the intracellular and extracellular concentrations, per mg of dried cells of Oscillatoria PCC 6506, of 7-epicylindrospermopsin (0.18 microg/mg and 0.29 microg/mg, respectively) and cylindrospermopsin (0.10 microg/mg and 0.11 microg/mg, respectively). We showed that these two toxins accumulated in the culture medium of Oscillatoria PCC 6506 but that the ratio (2.5 +/- 0.3) was constant with 7-epicylindrospermopsin being the major metabolite. We also determined the concentrations of these toxins in culture media of other Oscillatoria strains, PCC 6407, PCC 6602, PCC 7926, and PCC 10702, and found that, except for PCC 6602, they all produced 7-epicylindrospermopsin and cylindrospermopsin, with the former being the major toxin, except for PCC 7926, which produced very little 7-epicylindrospermopsin. All the cylindrospermopsin producers studied gave a PCR product using specific primers for the amplification of the cyrJ gene from genomic DNA.

Seasonal occurrence and toxicity of Microcystis spp. and Oscillatoria tenuis in the Lebna Dam, Tunisia

Physicochemical and biological water quality, including the total microcystin concentrations, was investigated for the first time from January to December 2005 in the Lebna Dam, Tunisia. Microcystin levels and characterization of the different microcystin variants present were measured by protein phosphatase (PP2A) inhibition assays and by LC/MS/MS, respectively. Nutrient values were high, with total inorganic nitrogen and phosphorus concentrations ranging from 0.05 to 8.4 mg L(-1) and from 0.03 to 1.37 mg L(-1), respectively. However, the chlorophyll-a concentrations were very low with a peak (5.32 microg L(-1)) on 20 September 2005 at 9 m depth water samples. Microscopic examination of the phytoplankton samples showed the dominance in the autumn of three morphospecies of the genus Microcystis and the species Oscillatoria tenuis. The total (particulate and dissolved) microcystin concentrations at the surface and at 9 m depth water samples ranged between 0.008 and 1.73, and 0.005 and 5.57 microg microcystin (MC)-LR equivalent L(-1), respectively, with a peak on 20 September. The presence of the microcystin synthetase genes (mcyA, -B, and -C) in the lysates of the three morphospecies of the genus Microcystis and the species O. tenuis indicated that these species were responsible for the microcystin production in this system. The analysis of the field cyanobacterial sample extract containing these species by LC/MS/MS revealed the presence of two microcystin variants: microcystin-LR (MC-LR) and microcystin-YR (MC-YR).