Effect of ultraviolet radiation on the metabolomic profiles of potentially toxic cyanobacteria

A rapid LC-MS/MS method for multi-class identification and quantification of cyanotoxins

Cyanobacteria can form harmful blooms in specific environmental conditions due to certain species producing toxic metabolites known as cyanotoxins. These toxins pose significant risks to public health and the environment, making it critical to identify and quantify them in food and water sources to avoid contamination. However, current screening methods only focus on a single class of cyanotoxins, limiting their effectiveness. Thus, fast and sensitive liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed to analyze eighteen cyanotoxins simultaneously. A simplified extraction procedure using lyophilized samples of cyanobacterial biomass was also used, eliminating the need for traditional solid-phase extraction methods. This method uses multiple reaction monitoring and allows accurate determination and quantification of eighteen cyanotoxins, including anatoxin-a, homoanatoxin-a, cylindrospermopsin, deoxy-cylindrospermopsin, nodularin, guanitoxin, seven microcystins (RR, [D-Asp3] RR, LA, LR, LY, LW, and YR), and five saxitoxins (gonyautoxins - GTX-1&4, GTX-2&3, GTX-5), decarbamoylgonyautoxin (dcGTX-2&3), and N-Sulfocarbamoylgonyautoxin (C1&C2), all in a short acquisition time of 8 min. Therefore, this method provides a simple and efficient approach to identify and quantify harmful compounds produced by cyanobacteria. Hence, this represents the first method to detecting guanitoxin among cyanotoxins. By expanding the range of toxins analyzed, this method can help ensure high-quality food and drinking water and protect recreational users from exposure to cyanotoxins.

Toxicological effects of cyanobacterial metabolites on zebrafish larval development

Freshwater cyanobacteria are known worldwide for their potential to produce toxins. However, these organisms are also found in marine, terrestrial and extreme environments and produce unique compounds, other than toxins. Nevertheless, their effects on biological systems are still barely known. This work tested extracts of different cyanobacterial strains against zebrafish (Danio rerio) larvae and analyzed their metabolomic profiles using liquid chromatography combined with mass spectrometry. Strains Desertifilum tharense, Anagnostidinema amphibium, and Nostoc sp. promoted morphological abnormalities such as pericardial edema, edema in the digestive system region, curvature of the tail and spine in zebrafish larvae in vivo. In contrast, Microcystis aeruginosa and Chlorogloeopsis sp. did not promote such changes. Metabolomics revealed unique compounds belonging to the classes of terpenoids, peptides, and linear lipopeptides/microginins in the nontoxic strains. The toxic strains were shown to contain unique compounds belonging to the classes of cyclic peptides, amino acids and other peptides, anabaenopeptins, lipopeptides, terpenoids, and alkaloids and derivatives. Other unknown compounds were also detected, highlighting the rich structural diversity of secondary metabolites produced by cyanobacteria. The effects of cyanobacterial metabolites on living organisms, mainly those related to potential human and ecotoxicological risks, are still poorly known. This work highlights the diverse, complex, and unique metabolomic profiles of cyanobacteria and the biotechnological potential and associated risks of exposure to their metabolites.

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

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

Metabolomics Applied to Cyanobacterial Toxins and Natural Products

The biological and chemical diversity of Cyanobacteria is remarkable. These ancient prokaryotes are widespread in nature and can be found in virtually every habitat on Earth where there is light and water. They are producers of an array of secondary metabolites with important ecological roles, toxic effects, and biotechnological applications. The investigation of cyanobacterial metabolites has benefited from advances in analytical tools and bioinformatics that are employed in metabolomic analyses. In this chapter, we review selected articles highlighting the use of targeted and untargeted metabolomics in the analyses of secondary metabolites produced by cyanobacteria. Here, cyanobacterial secondary metabolites have been didactically divided into toxins and natural products according to their relevance to toxicological studies and drug discovery, respectively. This review illustrates how metabolomics has improved the chemical analysis of cyanobacteria in terms of speed, sensitivity, selectivity, and/or coverage, allowing for broader and more complex scientific questions.

Metabolomic Insights of the Effects of Bacterial Algicide IRI-160AA on Dinoflagellate Karlodinium veneficum

Shewanella sp. IRI-160 is an algicidal bacterium that secretes an algicide, IRI-160AA. This algicide specifically targets dinoflagellates, while having no adverse effects on other algal species tested. Dinoflagellates exposed to IRI-160AA exhibited increased production of reactive oxygen species (ROS), DNA damage, and cell cycle arrest, implying a programmed pathway leading to cell death (PCD). Here, a metabolomic analysis was conducted on dinoflagellate Karlodinium veneficum and a control cryptophyte species Rhodomonas exposed to IRI-160AA to investigate the cellular mechanisms behind the physiological effects and the specificity of this algicide. Results of this research supported previous observations about physiological responses to the algicide. A suite of metabolites was identified that increased in the cell pellets of K. veneficum but not in Rhodomonas, including oxidative stress biomarkers, antioxidants, and compounds involved in DNA damage and PCD. Overall, the results of this study illustrated the metabolomic mechanisms underlying the algicidal effects of IRI-160AA on dinoflagellates. This research also provided insights and future directions for studies on the cellular response of dinoflagellates exposed to antagonistic bacteria in the environment.