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The cyanobacterial species Raphidiopsis raciborskii (Wołoszyńska) Aguilera et al. has a high invasiveness potential, which in less than a century leads to its cosmopolitan spread. In the temperate climate of Europe, R. raciborskii has been reported in many countries, but there is still a lack of detailed information about the current status of its distribution in lakes of Bulgaria, as a part of the southeastern range of its spread in Europe. We investigated the distribution of the species using data on the phytoplankton of 122 lakes surveyed during 13-years period (2009-2022). The species was found in 33 lakes (up to 324 m asl), and 14 new localities were registered during the studied period. The results reveal that the number of lakes with the presence of R. raciborskii (27 % of all research lakes) and its contribution to the total phytoplankton biomass, has increased significantly over the last decade. The species has successfully adapted and dominated the phytoplankton in 9 lakes, forming a bloom in 8 of them. The dominant position of R. raciborskii causes loss of species and functional diversity of phytoplankton and displaces the native bloom-forming cyanobacteria. Lakes with and without the species were compared based on the available data on bioclimatic and local environmental variables. Statistically significant differences were established with respect to water transparency, conductivity, maximum depth and maximum air temperature in the warmest month. Species distribution models (SDMs) were used to identify lakes in high risk of future invasion by R. raciborskii. The results of the SDMs implementation confirmed the high maximum air temperature and low water transparency to be important predictors of the occurrence of R. raciborskii in freshwater lakes in Bulgaria. In the areas with high summer temperatures the most suitable for R. raciborskii development were found to be shallow polymictic or medium deep lakes with small surface area and low water transparency. In areas with a suitable climate, the large, deep reservoirs with high transparency as well as macrophyte dominated lakes have a low probability of occurrence of R. raciborskii. Future colonization of lakes above 500 m asl (but most likely below 700 m asl) is also possible, especially in the conditions of global warming. SDMs account for climatic and biogeographic differences of lakes and could help in elucidating the underlying factors that control the occurrence and adaptation of R. raciborskii in a given area., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

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 unique prokaryotes, which are capable to perform oxygenic photosynthesis. Within these organisms, phycobilisomes (PBS) act as an antenna of the photosynthetic pigment apparatus. Phycobilisomes contain several phycobiliproteins (PBP): phycoerythrin (PE), phycocyanin (PC), allophycocyanin (APC) and phycoerythrocyanin (PEC). The application of phycobiliproteins in the biotechnology, food industry and medicine during the last years is rapidly increasing. The aim of our study was to assess the qualitative and quantitative content of phycoerythrin, phycocyanin, allophycocyanin and phycoerythrocyanin in 14 cyanobacterial strains kept in Plovdiv Algal Culture Collection (PACC) and 4 strains purchased from the Culture Collection of Autotrophic Organisms (CCALA). Our data demonstrated that three strains of Microcoleus autumnalis (PACC 5505, PACC 5522 and PACC 5527) have high potential to produce phycoerythrins (0.132, 0.201 and 0.136 mg/mL, respectively). Similarly, one Microcoleus autumnalis strain (PACC 5522) and one strain of Leptolyngbya boryana (CCALA 084) are suitable for biotechnological production of phycocyanins (0.051 and 0.264 mg/mL, respectively) as well as allophycocyanins (0.102 and 0.171 mg/mL, respectively). In addition, the data about the pigment content could be used as a biochemical marker for taxonomic purposes within the group. [ABSTRACT FROM AUTHOR]

Cyanoprokaryotes are widespread organisms, which dominate in different water basins. In the present study, we have investigated the diversity of this group and related physicochemical parameters in 35 standing water basins in Bulgaria. We found 29 cyanoprokaryotic species, which belong to 13 genera from the orders Synechococcales, Spirulinales and Oscillatoriales. The frequency quotient of each species was calculated. Information about the distribution of the identified species and typology of the water basins is also provided. [ABSTRACT FROM AUTHOR]

This article presents a summary of the research related to the taxonomic composition, algal blooms and toxic potential of representatives from Cyanoprokaryota (Cyanobacteria, Cyanophyta) in the coastal waters of the Bulgarian Black Sea area. Main strands of the algal research, including Cyanoprokaryota, are presented in a chronological order. The taxonomic composition of cyanoprokaryotic microorganisms, their importance as a part from the algal flora of the Bulgarian Black Sea coast and the main problems caused by this group organisms are discussed. This information could be used as a basis for future investigations related to the taxonomy, diversity, distribution and evaluation of the biological activity of cyanoprokaryotic species in the Black Sea and particularly in the Bulgarian coast area. [ABSTRACT FROM AUTHOR]

The polyphasic approach is the most progressive system that has been suggested for distinguishing and phylogenetically classifying Cyanoprokaryota (Cyanobacteria/Cyanophyta). Several oscillatorialean genera (Lyngbya, Phormidium, Plectonema, and Leptolyngbya) have problematic phylogenetic position and taxonomic state because of their heterogeneity and polyphyletic nature. To accurately resolve the phylogenetic relationship of some filamentous species (Nodosilinea bijugata, Phormidium molle, Phormidium papyraceum), we have performed phylogenetic analyses based on 16S rRNA gene and the phycocyanin operon (PC-IGS) by using maximum-likelihood (ML) tree inference methods. These analyses were combined with morphologi-cal re-evaluation. Our phylogenetic analyses support the taxonomic separation of genus Nodosilinea from the polyphyletic genus Leptolyngbya. Investigated Nodosilinea strains always formed a coherent genetic cluster supported with a high bootstrap value. The molecular phylogeny confirmed also the monophyly of the Wilmottia group. In addition, data reveal that although P. papyraceum is morphologically similar to Wilmottia murrayi, this species is genetically distinct. Strains from the newly formed genus Phormidesmis and some Phormidium priestleyi strains were clustered in a separate clade different from the typical Phormidium species, but without strong bootstrap support. [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]