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The diversity of aerobic anoxygenic phototrophs (AAPs) and rhodopsin-containing bacteria in the surface microlayer, water column, and epilithic biofilms of Lake Baikal was studied for the first time, employing pufM and rhodopsin genes, and compared to 16S rRNA diversity. We detected pufM-containing Alphaproteobacteria (orders Rhodobacterales, Rhizobiales, Rhodospirillales, and Sphingomonadales), Betaproteobacteria (order Burkholderiales), Gemmatimonadetes, and Planctomycetes. Rhodobacterales dominated all the studied biotopes. The diversity of rhodopsin-containing bacteria in neuston and plankton of Lake Baikal was comparable to other studied water bodies. Bacteroidetes along with Proteobacteria were the prevailing phyla, and Verrucomicrobia and Planctomycetes were also detected. The number of rhodopsin sequences unclassified to the phylum level was rather high: 29% in the water microbiomes and 22% in the epilithon. Diversity of rhodopsin-containing bacteria in epilithic biofilms was comparable with that in neuston and plankton at the phyla level. Unweighted pair group method with arithmetic mean (UPGMA) and non-metric multidimensional scaling (NMDS) analysis indicated a distinct discrepancy between epilithon and microbial communities of water (including neuston and plankton) in the 16S rRNA, pufM and rhodopsin genes.

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Biological aggregations, in particular photogranules, can be found in different environments as one of the forms of existence of microorganisms, algae and small invertebrates. As far as they are systems, in which multiple ecological functions are performed by different elements simultaneously, they are considered a promising means for use in wastewater treatment. This paper provides description and composition of photogranules for the first time discovered in mass, 2,5 m away from the water edge in Listvennichnyi Bay of Lake Baikal in October 2015. The photogranules were maroon, free-floating, with a diameter of 0,5 to 1,5 cm, and were not hollow. Their main component was radially divergent filaments of oscillatorian cyanobacteria dominated by the members of the genus Symplocastrum. Photogranules with a diameter of less than 1 cm contained a large number of filaments of Spirogyra sp. ster., which in recent years have become widespread in the littoral of Lake Baikal and in the Angara River. In addition, there were fragments of numerous filamentous green algae, as well as diatom cells with Didymosphenia spp. dominance. The identified taxa are typical for the stony littoral zone of the lake at the depths from 0 to 3 m. Photogranulation in Baikal may be the result of overproduction of bottom communities of algae and cyanobacteria under conditions of increased anthropogenic load in the shallow water zone. Probably, photogranules can act as one of the mechanisms that perform the functions of natural self-purification in Baikal.

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Abstract. Mass development of the cyanobacteria Dolichospermum (D. lemmermannii as the dominant species) was reported in the coastal zone of Bol shye Koty Bay (western coast of the southern basin), towards the end of July to the beginning of August in 2019. Blooms were observed as 1 1.5-m wide bands adjoining the shoreline and stretched uninterrupted over 2 km. Abundance of cyanobacteria in blooms varied within 7.2 71.9 thousand cell mL-1, with 0.73 7.20 g m-3 biomass attained. Maximal concentration was observed opposite the biological station of Irkutsk State University, a frequently visited place that was hosting participants of several conferences at that time. Hydrochemical analysis of samples collected four days after continuous heavy rains showed much higher concentrations of nutrients in contrast with the data obtained a week before (24 July), which is normal for that season. Nutrient concentrations were elevated relative to long term averages by 3 to 30 fold: with phosphate concentrations up to 0.200 mg L-1, ammonium ions 0.29 mg L-1, and nitrates 0.31 mg L-1. Possible reasons for the harmful freshwater cyanobacterial bloom that is unusual for this part of the lake are discussed. Excessive proliferation of common cyanobacteria D. lemmermannii in the open lake areas was affected by several factors: long-lasting heavy rains, zero wind, high air (from 13 15 at night to 29 in daytime) and water temperatures (from 15 to 19.2 ); and absence of isolated septic tanks in the nearshore zone.

Using the metagenomics approach and high throughput sequencing of the 16S rRNA gene amplicons, we studied the taxonomic diversity of nitrifying bacteria in microbial communities from epilithic biofilms and plankton of the littoral zone of Lake Baikal. The family Nitrosomonadaceae represents the diversity of ammonia-oxidizing bacteria; the genera Nitrospira (Nitrospirae) and Candidatus Nitrotoga (Gammaproteobacteria)-nitrite-oxidizing bacteria; and the phyla Nitrospinaeunidentified bacteria. Microbial communities from epilithic biofilms and the near-bottom water layer showed the highest diversity and those from the surface water layer-the lowest one. Among ammonia oxidizers, bacteria of the uncultured genus Ellin6067 (27 phylotypes) dominated and were ubiquitous, and among nitrite oxidizers-bacteria of the genus Nitrospira (7 phylotypes).