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As producers of biomass, cyanobacteria are a major part of the phytoplankton in a large number of water basins. Due to the cyanobacterial blooms and cyanotoxins produced, these organisms are recognized as a threat and ecological risk for water bodies. Released cyanotoxins may cause death of many organisms including birds and fish. Vaya Lake is the largest natural lake in Bulgaria. It is located on the Via Pontica migration route of birds between Europe and Africa. Since 2003, the lake has been declared as a "Wetland of international importance" under the Ramsar Convention. According to the literature data from 2002-2006, the Lake is defined as highly eutrophied due to strong anthropogenic pressure, but regular monitoring of the cyanobacterial blooms and presence of cyanotoxins after this period is missing. Taking into account the importance of this unique, protected ecosystem, our aim was to make a complete ecological assessment of the present state of Lake Vaya by using the phytoplankton, with an emphasis on cyanobacterial blooms and the presence of cyanotoxins. As results of the study, we 1) characterized the phytoplankton composition qualitatively and quantitatively; 2) evaluated the ecological status of the western and eastern part of the Lake; 3) identified the potential producers of cyanotoxins; 4) observed cyanobacterial blooms and discussed the influence of macrophytes on their spread; 5) measured the concentrations of the cyanotoxins MCs, CYL and STXs in water samples from both parts of the Lake. Our results indicated the need for continued observation of cyanobacterial composition, blooming and the presence of cyanotoxins in Lake Vaya. [ABSTRACT FROM AUTHOR]

Cyanobacteria are photosynthetic prokaryotes with cosmopolitan distribution. They are major producers of primary biomass and free oxygen in most of the freshwater and marine biomes on the planet. Under certain conditions of the environment, these organisms can evolve massively and cause the so-called "water blooms". Very often these blooms are toxic due to the ability of some cyanobacteria to produce dangerous toxins (cyanotoxins) with hepatotoxic, neurotoxic or dermatotoxic effects. This determines the cyanobacteria as an ecological risk for the aquatic ecosystems as well as a threat for the health of animals and humans. Climate changes also lead to an increase in the percentage of cyanobacterial blooms. Therefore, the investigation of the species composition of this group in the Bulgarian reservoirs, the tracking of the blooms frequencies as well as the assessment of their toxic potential is of great importance. Unfortunately, such data at this stage are scarce. This study presents data on the species composition and toxic potential of Cyanobacteria during the summer months of 2017 in five reservoirs (Batak, Dospat, Shiroka polyana, Golyam Beglik and Krichim dams) in the Western Rhodope Mountain. During the investigation period, except the representatives of Cyanobacteria, seven algal phyla (Chlorophyta, Bacillariophyta, Euglenophyta, Dinoflagellata, Cryptophyta, Chrysophyta and Xantophyta) were also found in the dams. The frequency and percentage of cyanobacteria were reported. A taxonomic list of the determined cyanobacterial species is given for each water body. In addition, a quantitative characteristic for each species (density and biomass) was performed. By using ELISA tests for cyanotoxins we have analyzed the presence of microcystins/nodularins (MCs/Nod) and saxitoxins (STXs). Cyanotoxins were found in four of the studied water basins - Dospat Dam, Batak Dam, Shiroka polyana Dam and Krichim Dam. [ABSTRACT FROM AUTHOR]

Cyanobacteria are prokaryotic organisms characterized by their ability to produce secondary metabolites with different biological activities. The aim of this work was to evaluate the in vitro and in vivo toxicity of the cosmopolitan freshwater cyanobacterium H. kuetzingii. An extract from H. kuetzingii and cyanobacterial growth media were assessed for presence of intracellular and extracellular toxins by in vitro tests using primary cell cultures from mouse kidney and fibroblasts, cell lines A549 and 3T3, a fish cell line RTgill-W1 as well as by a traditional in vivo mouse bioassay. The presence of toxicity was compared with the ELISA and HPLC data for corresponding cyanotoxins. In vitro tests showed pronounced cytotoxicity of the cyanobacterium extract and growth medium in which H. kuetzingii released potential extracellular toxic compounds as the mammalian cells were significantly more sensitive to exposure compared to the fish cells. Histopathological analyses of the liver and kidneys of treated mice showed pathological changes such as leukocyte infiltration and necrosis, changes in the proximal and distal convoluted tubules, lack of differentiation of Bowman's space, enlarged Bowman's capsules and massive hemorrhages. ELISA and HPLC analyses confirmed the presence of saxitoxins and microcystins at low concentrations. In addition, the histological analyses suggest that H. kuetzingii produces other, yet unknown toxic metabolites. Monitoring efforts are therefore required to evaluate the potential hazard for the freshwater aquatic systems and possible public health implications associated with this cyanobacterium. [ABSTRACT FROM AUTHOR]