Salinity-induced succession of phototrophic communities in a southwestern Siberian soda lake during the solar activity cycle.

A variety of lakes located in the dry steppe area of southwestern Siberia are exposed to rapid climatic changes, including intra-century cycles with alternating dry and wet phases driven by solar activity. As a result, the salt lakes of that region experience significant fluctuations in water level and salinity, which have an essential impact on the indigenous microbial communities. But there are few microbiological studies that have analyzed this impact, despite its importance for understanding the functioning of regional water ecosystems. This work is a retrospective study aimed at analyzing how solar activity-related changes in hydrological regime affect phototrophic microbial communities using the example of the shallow soda lake Tanatar VI, located in the Kulunda steppe (Altai Region, Russia, southwestern Siberia). The main approach used in this study was the comparison of hydrochemical and microscopic data obtained during annual field work with satellite and solar activity data for the 12-year observation period (2011-2022). The occurrence of 33 morphotypes of cyanobacteria, two key morphotypes of chlorophytes, and four morphotypes of anoxygenic phototrophic bacteria was analyzed due to their easily recognizable morphology. During the study period, the lake surface changed threefold and the salinity changed by more than an order of magnitude, which strongly correlated with the phases of the solar activity cycles. The periods of high (2011-2014; 100-250 g/L), medium (2015-2016; 60 g/L), extremely low (2017-2020; 13-16 g/L), and low (2021-2022; 23-34 g/L) salinity with unique biodiversity of phototrophic communities were distinguished. This study shows that solar activity cycles determine the dynamics of the total salinity of a southwestern Siberian soda lake, which in turn determines the communities and microorganisms that will occur in the lake, ultimately leading to cyclical changes in alternative states of the ecosystem (dynamic stability).

A novel bacteriobiont of the Arctic lichen Flavocetraria nivalis, Lichenifustis flavocetrariae gen. nov, sp. nov. demonstrating hydrolytic properties and containing a full set of the Calvin-Benson-Bassham cycle genes.

A Gram-negative, strictly aerobic, chemoorganotrophic, bacteriochlorophyll a-containing, slow-growing bacterium was isolated from the lichen Flavocetraria nivalis and designated strain BP6-180914 T. Cells of this strain were large nonmotile rods, which reproduced by binary fission. Cells grew under oxic conditions and were able to utilize sugars and several polysaccharides, including starch and pectin. Strain BP6-180914 T was psychrotolerant and moderately acidophilic growing at 4-35 °C (optimum 20-28 °C) and between pH 4.0 and 7.5 (optimum 4.5-5.5). The major fatty acids were C18:1ω7c, C19:0 cyclo, C16:0 and C18:0. The polar lipids were diphosphatidylglycerols, phosphatidylglycerols, phosphatidylethanolamines, phosphatidylcholines, unidentified aminolipids, and a number of glycolipids, the major one being an unidentified glycolipid. The quinone was Q-10. The DNA G + C content was 63.65%. Comparative 16S rRNA gene sequence analysis revealed that strain BP6-180914 T was a member of the order Hyphomicrobiales and belonged to the family Lichenihabitantaceae defined by the lichen-dwelling facultative aerobic chemo-organotroph Lichenihabitans psoromatis (92.7% sequence similarity). The results of phylogenomic and genomic relatedness analyses showed that strain BP6-180914 T could clearly be distinguished from other species in the order Hyphomicrobiales with average nucleotide identity values of < 74.05% and genome-to-genome distance values of < 21.1%. The AAI value of 65.9% between strain BP6-180914 T and L. psoromatis allowed us to assign this strain to the novel genus of the family Lichenihabitantaceae. Therefore, it is proposed that strain BP6-180914 T represents a novel species in a new genus, Lichenifustis flavocetrariae gen. nov., sp. nov.; strain BP6-180914 T (= KCTC 92872 T = VKM B-3641 T = UQM 41506 T) is the type strain.

Biogeochemical Activity of Methane-Related Microbial Communities in Bottom Sediments of Cold Seeps of the Laptev Sea.

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.

History of the Study of the Genus Thiothrix: From the First Enrichment Cultures to Pangenomic Analysis.

Representatives of the genus Thiothrix are filamentous, sulfur-oxidizing bacteria found in flowing waters with counter-oriented sulfide and oxygen gradients. They were first described at the end of the 19th century, but the first pure cultures of this species only became available 100 years later. An increase in the number of described Thiothrix species at the beginning of the 21st century shows that the classical phylogenetic marker, 16S rRNA gene, is not informative for species differentiation, which is possible based on genome analysis. Pangenome analysis of the genus Thiothrix showed that the core genome includes genes for dissimilatory sulfur metabolism and central metabolic pathways, namely the Krebs cycle, Embden-Meyerhof-Parnas pathway, glyoxylate cycle, Calvin-Benson-Bassham cycle, and genes for phosphorus metabolism and amination. The shell part of the pangenome includes genes for dissimilatory nitrogen metabolism and nitrogen fixation, for respiration with thiosulfate. The dispensable genome comprises genes predicted to encode mainly hypothetical proteins, transporters, transcription regulators, methyltransferases, transposases, and toxin-antitoxin systems.

Biogeochemical Factors of Cs, Sr, U, Pu Immobilization in Bottom Sediments of the Upa River, Located in the Zone of Chernobyl Accident.

Laboratory modeling of Cs, Sr, U, Pu immobilization by phytoplankton of the river Upa, affected after the Chernobyl accident, has been carried out. Certain conditions are selected for strong fixation of radionuclides in bottom sediments due to biogeochemical processes. The process of radionuclide removal from the water phase via precipitation was based on their accumulation by phytoplankton, stimulated by nitrogen and phosphorus sources. After eight days of stimulation, planktonic phototrophic biomass, dominated by cyanobacteria of the genus Planktothrix, appears in the water sample. The effectiveness of U, Pu and Sr purification via their transfer to bottom sediment was observed within one month. The addition of ammonium sulfate and phosphate (Ammophos) led to the activation of sulfate- and iron-reducing bacteria of the genera Desulfobacterota, Desulfotomaculum, Desulfosporomusa, Desulfosporosinus, Thermodesulfobium, Thiomonas, Thiobacillus, Sulfuritallea, Pseudomonas, which form sulphide ferrous precipitates such as pyrite, wurtzite, hydrotroillite, etc., in anaerobic bottom sediments. The biogenic mineral composition of the sediments obtained under laboratory conditions was verified via thermodynamic modeling.

Ecology and biogeography of the 'marine Geitlerinema' cluster and a description of Sodalinema orleanskyi sp. nov., Sodalinema gerasimenkoae sp. nov., Sodalinema stali sp. nov. and Baaleninema simplex gen. et sp. nov. (Oscillatoriales, Cyanobacteria).

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.

Methanogenesis in the Lake Elton saline aquatic system.

Cultivation and molecular approaches were used to study methanogenesis in saline aquatic system of the Lake Elton (southern Russia), the largest hypersaline lake in Europe. The potential rates of hydrogenotrophic, acetoclastic, methylotrophic and methyl-reducing methanogenesis and diversity of the growth-enriched for by adding electron donors methanogenic communities were studied in the sediment slurry incubations at salinity range from 7 to 275 g/L. The most active pathway detected at all salinities was methylotrophic with a dominance of Methanohalobium and Methanohalophilus genera, at salt saturation and moderately halophilic Methanolobus and Methanococcoides at lower salinity. The absence of methane production from acetate, formate and H2/CO2 under hypersaline conditions was most probably associated with the energy constraints. The contribution of hydrogenotrophic, acetoclastic, and methyl-reducing methanogens to the community increases with a decrease in salinity. Temperature might play an important regulatory function in hypersaline habitats; i.e. methylotrophic methanogens and hydrogenotrophic sulfate-reducing bacteria (SRB) outcompeting methyl-reducing methanogens under mesophilic conditions, and vice versa under thermophilic conditions. An active methane production together with negligible methane oxidation makes hypersaline environments a potential source of methane emission.

The patterns of nitrogen fixation in haloalkaliphilic phototrophic communities of Kulunda Steppe soda lakes (Altai, Russia).

Nitrogen fixation (NF) of phototrophic communities was studied in a number of soda lakes with a wide range of salinity (25-400 g/l) located in Kulunda Steppe (Altai, Russia) during several summer seasons (2011-2016). The phototrophic communities were represented by the algal-bacterial Ctenocladus communities or cyanobacterial biofilms dominated by heterocystous and non-heterocystous cyanobacteria and purple sulfur bacteria Ectothiorhodospira sp. (up to 210 g/l) and endoevaporitic Euhalothece communities dominated by the extremely salt-tolerant unicellular cyanobacterium Euhalothece sp. and Ectothiorhodospira sp. (above 350 g/l). Salinity was the major factor influencing the composition and NF potential of the phototrophic communities. The communities dominated by vegetative heterocystous cyanobacteria exhibited light-independent NF at total salinity up to 60 g/l. The communities dominated by non-heterocystous cyanobacteria exhibited light-dependent NF in a range of 55-100 g/l, but it was significantly suppressed at 100 g/l. At 160-200 g/l the dark heterotrophic NF was a prevailing process if communities didn't contain Euhalothece sp. At salt-saturating ranges above 350 g/l, light-dependent NF associated with the Euhalothece communities was detected. A statistically significant positive correlation between the NF and diurnal light intensity was found in all samples of communities dominated by non-heterocystous cyanobacteria in contrast to communities dominated by heterocystous cyanobacteria with insignificant correlation coefficients.

Effect of salinity on diazotrophic activity and microbial composition of phototrophic communities from Bitter-1 soda lake (Kulunda Steppe, Russia).

Bitter-1 is a shallow hypersaline soda lake in Kulunda Steppe (Altai region, Russia). During a study period between 2005 and 2016, the salinity in the littoral area of the lake fluctuated within the range from 85 to 400 g/L (in July of each year). Light-dependent nitrogen fixation occurred in this lake up to the salt-saturating conditions. The rates increased with a decrease in salinity, both under environmental conditions and in laboratory simulations. The salinities below 100 g/L were favorable for light-dependent nitrogen fixation, while the process was dramatically inhibited above 200 g/L salts. The analysis of nifH genes in environmental samples and in enrichment cultures of diazotrophic phototrophs suggested that anaerobic fermenting and sulfate-reducing bacteria could participate in the dark nitrogen fixation process up to soda-saturating conditions. However, we cannot exclude the possibility that haloalkaliphilic nonheterocystous cyanobacteria (Euhalothece sp. and Geitlerinema sp.) and anoxygenic purple sulfur bacteria (Ectothiorhodospira sp.) might also play a role in the process at light conditions. The heterocystous cyanobacterium Nodularia sp. develops at low salinity (below 80 g/L) that is not characteristic for Bitter-1 Lake and thus does not make a significant contribution to the nitrogen fixation in this lake.