Toxic potential of microcystin-containing cyanobacterial extracts from three Romanian freshwaters

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

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

Cyanotoxins: characteristics, production and degradation routes in drinking water treatment with reference to the situation in Serbia

Cyanobacteria are members of phytoplankton of the surface freshwaters. The accelerated eutrophication of freshwaters, especially reservoirs for drinking water, by human activity has increased the occurrence and intensity of cyanobacterial blooms. They are of concern due to their ability to produce taste and odors compounds, a wide range of toxins, which have a hepatotoxic, neurotoxic, cytotoxic and dermatotoxic behavior, being dangerous to animal and human health. Therefore, the removal of cyanobacteria, without cell lysis, and releasing of intracellular metabolites, would significantly reduce the concentration of these metabolites in the finished drinking water, as a specific aim of the water treatment processes. This review summarizes the existing data on characteristics of the cyanotoxins, their productions in environment and effective treatment processes to remove these toxins from drinking water.

Detection of microcystin-producing Microcystis in Guanqiao Lake using a sandwich hybridization assay

Based on sequence analyses of the mcyJ gene from Microcystis strains, a probe pair TJF and TJR was designed and a sandwich hybridization assay (SHA) was established to quantitatively detect microcystin-producing Microcystis. Through BLAST and cyanobacterial culture tests, TJF and TJR were demonstrated to be specific for microcystin-producing Microcystis. A calibration curve for the SHA was established, and the lowest detected concentration was 100 cells·mL(-1). Laboratory cultures and field samples from Guanqiao Lake were analyzed with both the SHA and microscopy. The cell number of microcystin-producing Microcystis and that of total Microcystis were compared. The biotic and abiotic components of the samples were of little disturbance to the SHA. In this study, a SHA was established to detect Microcystis, providing an alternative to PCR-ELISA and real-time PCR technology.

Impact of microcystin containing diets on physiological performance of Nile tilapia (Oreochromis niloticus) concerning stress and growth

Diets containing Microcystis with considerable amounts of the cyanotoxin microcystin-LR (MC-LR) were fed to determine their impact on the physiological performance of the omnivorous Nile tilapia (Oreochromis niloticus) with regard to stress and growth performance. Four different diets were prepared based on a commercial diet (control, MC-5% [containing 5% dried Microcystis biomass], MC-20% [containing 20% dried Microcystis biomass], and Arthrospira-20% [containing 20% dried Arthrospira sp. biomass without toxin]) and fed to female Nile tilapia. Blood and tissue samples were taken after 1, 7, and 28 d, and MC-LR was quantified in gills, muscle, and liver by using high-performance liquid chromatography (HPLC). Only in the liver were moderate concentrations of MC-LR detected. The stress hormone cortisol and glucose were analyzed from plasma, suggesting that all modified diets caused only minor to moderate stress, which was confirmed by analyses of hepatic glycogen. In addition, the effects of the different diets on growth performance were investigated by determining gene expression of hypophyseal growth hormone (GH) and hepatic insulin-like growth factor-I (IGF-I). For all diets, quantitative reverse transcription-polymerase chain reaction (RT-qPCR) demonstrated no significant effect on gene expression of the major endocrine hormones of the growth axis, whereas classical growth data, including growth and feed conversion ratio, displayed slight inhibitory effects of all modified diets independent of their MC-LR content. However, no significant change was found in condition or hepatosomatic index among the various diets, so it seems feasible that dried cyanobacterial biomass might be even used as a component in fish diet for Nile tilapia, which requires further research in more detail.

Oral administration of cyanobacterial bloom extract induced the altered expression of the PP2A, Bax, and Bcl-2 in mice

The frequent occurrences of the toxic cyanobacterial (specifically Microcystis aeruginosa) bloom are becoming a global environmental issue. Lots of researches have been focused on the pure cyanobacterial toxins, but little on the natural cyanobacterial bloom. This study was undertaken to investigate the effect of the natural cyanobacterial bloom extract on the expression of proteins, which have been shown to be affected by pure microcystins. In current study, the cyanobacterial bloom extract has been administered orally to ICR mice for 7 days with different dosages. The expression level of PP2A, Bcl-2, and Bax was measured via western blotting. The results showed that after 7 days of exposure to cyanobacteria extract, in mice liver tissue, the expression level of PP2A and Bax was increased significantly between the control and treatment groups, but there is no significant change on the Bcl-2 expression. This is the first report to describe the altered expression of PP2A in vivo when mice exposure to natural water blooms extract that means many cellular pathways would be interfered via the change of PP2A activity.