The composition and macroscopic structure of the floating oxygenic phototrophic communities from Kulunda steppe soda lakes (Cock Soda Lake, Tanatar VI, and Bitter Lake 3) was described based on the data of the 2011 and 2012 expeditions (Winogradsky Institute of Microbiology). The algo-bacterial community with a green alga Ctenocladus circinnatus as an edificator was the typical one. Filamentous Geitlerinema sp. and Nodosilinea sp. were the dominant cyanobacteria. Apart from C. circinnatus, the algological component of the community contained unicellular green algae Dunaliella viridis and cf. Chlorella minutissima, as well as diatoms (Anomoeoneis sphaerophora, Brachysira brebissonii, Brachysira zellensis, Mastogloia pusilla var. subcapitata, Nitzschia amphibia, Nitzschia communis, and Nitzschia sp.1). The latter have not been previously identified in the lakes under study. In all lakes, a considerable increase in salinity was found to result in changes in the composition and macroscopic structure of algo-bacterial communities.

Bottom sediments at methane discharge sites of the Laptev Sea shelf were investigated. The rates of microbial methanogenesis and methane oxidation were measured, and the communities responsible for these processes were analyzed. Methane content in the sediments varied from 0.9 to 37 µmol CH₄ dm⁻³. Methane carbon isotopic composition (δ¹³C-CH₄) varied from −98.9 to −77.6‰, indicating its biogenic origin. The rates of hydrogenotrophic methanogenesis were low (0.4–5.0 nmol dm⁻³ day⁻¹). Methane oxidation rates varied from 0.4 to 1.2 µmol dm⁻³ day⁻¹ at the seep stations. Four lineages of anaerobic methanotrophic archaea (ANME) (1, 2a–2b, 2c, and 3) were found in the deeper sediments at the seep stations along with sulfate-reducing Desulfobacteriota. The ANME-2a-2b clade was predominant among ANME. Aerobic ammonium-oxidizing Crenarchaeota (family Nitrosopumilaceae) predominated in the upper sediments along with heterotrophic Actinobacteriota and Bacteroidota, and mehtanotrophs of the classes Alphaproteobacteria (Methyloceanibacter) and Gammaproteobacteria (families Methylophilaceae and Methylomonadaceae). Members of the genera Sulfurovum and Sulfurimonas occurred in the sediments of the seep stations. Mehtanotrophs of the classes Alphaproteobacteria (Methyloceanibacter) and Gammaproteobacteria (families Methylophilaceae and Methylomonadaceae) occurred in the sediments of all stations. The microbial community composition was similar to that of methane seep sediments from geographically remote areas of the global ocean.

Filamentous cyanobacteria belonging to the ‘marine Geitlerinema’ cluster are spread worldwide in saline environments and considered to play an important ecological role. However, the taxonomy of this group remains unclear. Here, we analyzed the phylogeny, ecology and biogeography of the ‘marine Geitlerinema’ cluster representatives and revealed two subclusters: (1) an ‘oceanic’ subcluster containing PCC7105 clade and black band disease (BBD) clade with free-living and pathogenic strains distributed in Atlantic, Indian and Pacific Ocean-related localities, and (2) a Sodalinema subcluster containing free-living strains from marine, hypersaline, saline-alkaline and soda lake habitats from the Eurasian and African continents. Polyphasic analysis using genetic and phenotypic criteria demonstrated that these two groups represent separate genera. Representatives of Sodalinema subcluster were phylogenetically attributed to the genus Sodalinema. Our data expand the ecological and geographical distribution of this genus. We emended the description of the genus Sodalinema and proposed three new species differing in phylogenetic, geographic and ecological criteria: Sodalinema orleanskyi sp. nov., Sodalinema gerasimenkoae sp. nov. and Sodalinema stali sp. nov. Additionally, a new genus and species Baaleninema simplex gen. et sp. nov. was discribed within the PCC7105 clade. By this, we put in order the current confusion of the ‘marine Geitlerinema’ group and highlight its ecological diversity.

Cyanobacteria are a group of oxygenic phototrophs that have existed for at least 3.5 Ga. Photosynthetic CO2assimilation by cyanobacteria occurs via the Calvin cycle, with RuBisCO, its key enzyme,...

Microbialites occur in a number of modern soda lakes, but the formation of dolomite stromatolites in these environments is rare. Microbial metabolic activities are considered to influence precipitation of carbonate minerals (including dolomite) in marine, hypersaline and slightly alkaline environments due to their capacity to buffer pH of the local environmental settings. Hydrochemical features of hypersaline alkaline Petukhovskoe Soda Lake are already favourable for the precipitation of carbonate minerals, and the metabolic activities of microorganisms may not be significant in this type of environment. Stromatolites from this lake provide an excellent opportunity for the study of recent natural dolomite formation in the highly saturated soda environment. To understand the genesis of these stromatolites and to provide insight into environmental aspects of its formation, we have made a detailed structural and mineralogical description with the use of light and scanning electron microscopy, infrared spectroscopy and X‐ray analysis. Due to the special fluctuating conditions of sedimentation in the lake, stromatolites contain both layers with chemogenic precipitation of minerals and layers with fossilized algal, cyanobacterial and coccoid bacterial forms. The presence of dolomite, calcite and Mg calcites with different content of magnesium is detected. The primary independent binding of Mg and Si with the following binding of Ca in the pericellular and released exopolysaccharides is shown. Extracellular polymeric substances (EPS) and fluctuating hydrological regimen of the Petukhovskoe Soda Lake are considered to play the key role in the precipitation of Ca–Mg carbonates including dolomite.