An area of discolored water 50 m wide and 30 m long was found in September 2017 close to the dam of the Irkutsk hydroelectric power station. Water from this spot was sampled for investigation in the present study. Microscopic analysis revealed that the suspended matter in the sample was composed of clumps of filaments, vegetative cells, akinetes and heterocysts that formed short filaments and solitary cells. This matter was found to consist of partially degraded cells of the cyanobacterium Dolichospermum lemmermannii. Nucleotide sequencing of DNA isolated from the biomass revealed the presence of the sxtA gene which is involved in the synthesis of saxitoxin. Water from the polluted area contained 600 ± 100 μg L⁻¹ saxitoxin as measured by HPLC-MS with pre-column modification of the toxin with 2,4-dinitrophenylhydrazine. Immunoassay analysis (ELISA) showed a concentration of saxitoxins in the water of 2900 ± 900 μg L⁻¹. Hydrochemical and microbiological analyses suggested the contaminated area appeared as a result of a D. lemmermannii bloom, followed by its decay and release of saxitoxin and nutrients. The present paper describes the results of a case study. Better understanding of the phenomenon will depend on the possibility to perform implementation of a large-scale monitoring program.

For the first time, microcystin-producing cyanobacteria have been detected in Khubsugul, which is ancient, pristine and one of the world’s largest lakes. The microcystin synthetase genes belonged to the genera Nostoc, Microcystis and possibly Snowella spp. No microcystins were found in the water of the lake. Using the HPLC-HRMS/TOF, five microcystin congeners were identified in biofilms from stony substrates sampled in the coastal zone. The concentration of microcystins in biofilms was low: 41.95 µg g⁻¹ d. wt. by ELISA and 55.8 µg g⁻¹ d. wt. using HPLC. The taxonomic composition of planktonic and benthic cyanobacterial communities was determined by means of microscopy and high-throughput sequencing of 16S rDNA amplicons. Nostocales cyanobacteria dominated benthos of Lake Khubsugul and Synechococcales—plankton. The abundance of cyanobacteria was low both in plankton and benthos; there was no mass development of cyanobacteria. Hydrochemical and microbiological analyses showed that the water in the lake was clean; the number of faecal microorganisms was significantly below the acceptable guideline values. Hydrochemical and hydrophysical parameters, and the concentration of chlorophyll a, were low and within the range of values recorded in the 1970s to 1990s, and corresponded to the oligotrophic state of the lake. There were no signs of anthropogenic eutrophication of the lake and no conditions for the cyanobacterial blooms.

В планктоне водоёмов Байкальского региона и в прибрежной зоне оз. Байкал, начиная с 2005 г., обнаруживаются цианобактерии, содержащие гены синтеза токсинов и способные продуцировать токсины. Генетический анализ показал, что последовательности генов синтеза микроцистинов принадлежат видам родов Microcystis и Dolichospermum; генов паралитических токсинов моллюсков - представителям родов Anabaena/Dolichospermum/Aphanizomenon. Концентрация микроцистинов в воде превышала нормативы для питьевой воды в оз. Котокельское и в Усть-Илимском водохранилище, сакситоксина - в Иркутском водохранилище и в заливе Куркут оз. Байкал. В 2015 г. впервые выявлена продукция токсинов бентосными цианобактериями оз. Байкал, концентрация варьировала в диапазоне 29,8-3050 мкг/кг сухого веса (микроцистины) и 21-29390 мкг/г сухого веса (сакситоксин и его производные). Для оценки реальной угрозы здоровью человека необходима разработка гигиенических нормативов содержания цианотоксинов в...

Microcystis, a potentially toxigenic cyanobacterium known to form extensive blooms in eutrophic lakes globally, was investigated in the cold oligotrophic Lake Baikal. We report the isolation of two Microcystis strains, Microcystis aeruginosa and M. novacekii, and document the presence of the latter species in Lake Baikal for the first time. In M. aeruginosa strain BN23, we detected the microcystin synthetase gene mcyE. Liquid chromatography-mass spectrometry revealed the presence of two microcystin variants in BN23, with microcystin-LR, a highly potent toxin, being the dominant form. The concentration of MC-LR reached 540 µg/g dry weight. In contrast, M. novacekii strain BT23 lacked both microcystin synthesis genes and detectable toxins. The habitat waters were characterized as oligotrophic with minor elements of mesotrophy, exhibiting low phytoplankton biomass dominated by the chrysophyte Dinobryon cylindricum (76–77% of biomass), with cyanobacteria contributing 8–10%. The contribution of Microcystis spp. to the total phytoplankton biomass could not be quantified as they were exclusively found in net samples. The water temperature at both sampling stations was ~19 °C, which is considerably lower than optimal for Microcystis spp. and potentially conducive to enhanced microcystin production in toxigenic genotypes.

Cyanobacteria of the genus Tychonema are common inhabitants of freshwater bodies in a temperate zones. In Lake Baikal, Tychonema sp. was first reported in 2014. It grows excessively on the bottom on almost all substrates types, forming epiphytic and epizoic biofilms, and its role in the mass mortality events affecting of endemic Baikal sponges is discussed. The cyanobacterial strain BBK16 (=IPPAS B-2063^T), isolated from a biofilm on a log pier in the Bolshiye Koty settlement in 2016, was used for further taxonomic characterization. Key morphological features of strain BBK16 include its growth as a creeping mat, highly motile trichomes that are sometimes narrowed and hooked at the ends, and the presence of rounded-conical apical cells with a calyptra. Strain ultrastructure (fascicular parietal thylakoids and type D cell division) differs from Tychonema species with radial thylakoids but aligns with other genera in the Microcoleaceae family. A comprehensive analysis, including 16S rRNA gene phylogeny, conserved protein phylogeny, and whole-genome comparisons, confirmed its placement within the genus Tychonema. The average nucleotide identity, average amino acid identity and digital DNA–DNA hybridization values between strain BBK16 and T. bourrellyi FEM GT703 were 90.7%, 91.1% and 43.3%, respectively, indicating values below the standard thresholds for species delineation. Based on combined morphological, genomic, and ecological evidence, we propose the name Tychonema litorale sp. nov. for strain BBK16, a novel species described in accordance with the International Code of Nomenclature for Algae, Fungi, and Plants.