Nº 6 (2023)

The analysis of sanitary-bacteriological assessment of water quality in the littoral and pelagic zones of Lake Baikal for the whole period of microbiological studies of the ecosystem was carried out. It was established that such studies were single in the last century and only from the end of the century they began to be carried out all over the lake, and now they are carried out annually in the spring, summer and autumn periods over the whole water area of Lake Baikal and in the estuaries of large tributaries. The water quality of the lake was assessed and unfavourable areas in the littoral zone were identified for exceeding SanPiN standards. In 2021-2023, wastewater samples were taken after the treatment facilities in the Slyudyanka and Severobaikalsk towns, low efficiency of disinfection and inflow of opportunistic and pathogenic bacteria into Lake Baikal (bacterial pollution) were revealed. The scheme and periodicity of sanitary-bacteriological monitoring of the Lake Baikal ecosystem is proposed.

Phytoplankton has higher species richness in summer, when water temperatures are higher than in other seasons in aquatic ecosystems. Here, we characterized phytoplankton communities using microscopy and environmental parameters (temperature, pH, transparency) in the southern basin of Lake Baikal and Irkutsk Reservoir, which is directly connected with the lake as it is the upper part of Angara River, the Lake Baikal outlet. Surface water temperature was 10.1-18.4 °С in the southern basin of Lake Baikal and 14.9-20.0 °С was in Irkutsk Reservoir, pH values were similar both in the lake and the reservoir (8.09-8.44 and 7.96-8.28, respectively), and Secchi disc water transparency was 4.5-9.0 m in the lake and 2.5-4.5 m in the reservoir. The phytoplankton community included 104 species from 7 high-rank taxa such as Chrysophyta (36), Chlorophyta (30), Bacillariophyta (22), Cyanobacteria (11), Cryptophyta (2), Dinophyta (2), and Haptophyta (1). Species composition of summer phytoplankton communities of the Irkutsk Reservoir and the southern basin of Lake Baikal were different, however the community composition in terms of high-level phylotypes was very similar. At the same time, a large number of small-cell cyanobacteria were identified in the lake. A high species richness of Chrysophyta, genus Dinobryon (11 species) and silica-scaled chrysophytes (22) was founded. The composition of dominant species of the southern basin of Lake Baikal and Irkutsk Reservoir became wider compared to data published earlier, and included Cyanodictyon planctonicum, Cyanodictyon sp., Microcystis sp., Dinobryon sociale, Dinobryon sociale var. americanum, Chlorella vulgaris and Mychonastes homosphaera.

We performed high-throughput sequencing of microbial community with cyanobacterium Tychonema sp. BBK16 and heterotrophic bacteria in vitro. Representatives of the phylum Pseudomonadota/Proteobacteria, the bacteria Hydrogenophaga, Sphingomonas, Paucibacter, Aminobacter, Devosia, Tahibacter, and Bosea dominate and coexist with the cyanobacterium for a long period of cultivation. It was found that this cyanobacterium is an edificator of this community providing the microbiome with organic matter. Metabolic features of heterotrophic bacteria based on reconstructed genomes are presented. The main processes of carbon and nitrogen metabolism in the biofilm are carbohydrate and amino acid metabolism, as well as processes regulating the relationships between members of this consortium. Hydrogenophaga sp. and Tychonema sp. BBK16 show carbon autotrophy due to the Calvin–Benson–Bassham (СВВ) cycle, while Sphingomonas sp. due to the glyoxylate pathway of metabolism. The biofilm also contains the anoxygenic photoheterotroph Bosea sp. using light energy to transform organic matter. Aminobacter sp. is an active degrader of complex organics, which possesses methylotrophy and supplies hydrogen for oxidation by Hydrogenophaga sp., Paucibacter sp., also supplies hydrogen for this community. Sphingomonas, Tychonema and Paucibacter release phosphate from organic compounds providing phosphorus to this consortium.

Effects of plastic nanoparticles on the Baikal siliceous sponge Lubomirskia baicalensis (Pallas, 1773), including the whole organism and primmorphs, were studied. A vital fluorescence dye was applied to visualize the spicules formed during the experiment. Polystyrene, polyvinyl chloride, and poly(methyl methacrylate) nanoparticles were found to be able to penetrate into the sponge body and cause toxic effects (decreased spicule production) starting from concentrations of 0.005-0.01 mg/L. This is a relatively high concentration, unthinkable in normal water bodies. On the other hand, the duration of the experiment (three months) is negligible compared to the life span of the sponge. Further experiments should aim to elucidate the fate of nanoplastics within sponges, the balance between plastic consumption, excretion and degradation, possibly involving sponge symbionts.