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Data indicating the important role of microorganisms in the formation of nodular monazite (NM) (kularite) of the Kular Range, Republic of Sakha (Yakutia), are presented. The NM contains microorganisms (cyanobacteria) replaced by REE-bearing phosphate (monazite) in the form of stromatolitic microedifices, as well as framboidal Fe sulfides in monazite. The Corg isotopic composition of kularite corresponds to biogenic carbon: the δ13С values vary from –22.2 to –22.3‰. [ABSTRACT FROM AUTHOR]

Although thermokarst alas lakes of Central Yakutia are of great climatic and economic importance, there is currently virtually no information on microbial communities and microbial processes in these lakes. This paper characterizes the hydrochemical features and presents a primary analysis of the diversity of planktonic microbial communities in three alas lakes of Central Yakutia—Tyungulyu, Taby, and Kharyyalakh. It was shown that in terms of the water physicochemical composition, the studied lakes were quite typical for this region; they had increased alkalinity and trophicity, but differed from each other in microbiological indicators. Chemoheterotrophic prokaryotes predominated in the studied planktonic communities, but a significant proportion of the 16S rRNA gene sequences were most similar to uncultured microorganisms whose functional potential is still unknown. [ABSTRACT FROM AUTHOR]

Depending on the season, the primary production of planktonic communities determined by radiotracer analysis varied within a broad range, from 6 to 314 µg C/(L h). Primary production in cyanobacterial mats was 4.2‒10.9 × 103 µg C/(dm3 h), and Chl a content varied from 6‒13 to 132‒140 mg Chl a/m2. For the plankton, the highest values were revealed in summer (25‒46 mg Chl a/m3), with the maximum in August (223 mg Chl a/m3). High abundance of bacterioplankton (0.3‒7.4 × 106 cells/mL) and massive growth of diatoms (0.15 × 106 cells/mL) with predominance of the genus Chaetoceros were found. Sulfate reduction rates varied from 0.037 µmol S/(dm3 h) in the upper reach to 61.87 µmol S/(dm3 h) in the river mouth. [ABSTRACT FROM AUTHOR]

The results of a long-term electron microscopic study of Kamchatka geyserites are presented showing biological remains of unique preservation and a wide variety of cyanobacteria silicification types. The data obtained made it possible to consider the geyserites of Kamchatka as a model object for bacterial-paleontological studies. [ABSTRACT FROM AUTHOR]

A basic knowledge of the features of modern microorganisms can be useful for interpreting microfossils in bacterial-paleontological studies. This article analyzes the diversity of morphological forms of prokaryotic microorganisms, provides data on their size range in comparison with eukaryotic microorganisms and viruses, and describes the principles of modern prokaryotic taxonomy. The paper also discusses some aspects of prokaryotic cytology that play a key role in the formation of biomarkers (“molecular fossils”) and mineral precipitation. [ABSTRACT FROM AUTHOR]

The diurnal dynamics of methane content in the near-bottom phototrophic biomass of the shallow soda lake Bitter 1 (Gorchina 1) with a salinity of 30 g/L during the study period was investigated. The community was dominated by filamentous cyanobacteria, although no layered mat was formed. The maximum value of methane content up to 202.4 nmol CH4/cm3 was revealed in the morning hours, which significantly exceeded the night values (28.9–42.8 nmol CH4/cm3). Comparison of data on the content of methane with the relative abundance of cyanobacteria, methanogenic archaea, and methanotrophic bacteria during the twenty-four hours indicated that active processes of the methane cycle in soda lakes occurred not only in the sediments, but also in the near-bottom cyanobacterial communities. Methane content in the biomass of such a community is the result of a balance between the processes of its release by methanogens, consumption by methanotrophic bacteria, and natural degassing. It is assumed that the morning peak of methane content is associated with the release of hydrogen by diazotrophic cyanobacteria, which stimulates the development and activity of hydrogenotrophic methanogens of the genus Methanocalculus. [ABSTRACT FROM AUTHOR]

Modern microbialites formed in soda-saline and soda lakes are of interest as model systems for studying geobiological interactions in the Precambrian, when such geochemical settings were widespread. This work describes the structure and mineral composition of microbialites from the soda-saline Laguna de Los Cisnes (Isla Grande, Tierra del Fuego, Chile), and also characterizes the biodiversity of microorganisms involved in their formation. The microbialites consist mainly of carbonate minerals, of which monohydrocalcite is of particular interest. It was shown that the formation of microbialites occurs under alkaline conditions in the presence of taxonomically and functionally diverse microorganisms and in direct contact with exopolysaccharides produced by the microbial community. [ABSTRACT FROM AUTHOR]

Methane oxidation rates and diversity of methane-oxidizing microorganisms were studied in the upper sediment layers of the Laptev Sea (methane seep area, Lena fore-delta, shelf, and upper slope not affected by seeps and river flow). The highest methane concentrations and methane oxidation rates (up to 1.16 µmol СН4 dm−3 day−1) were revealed at the seep stations. Carbon dioxide was the main product of methane oxidation at all stations. Sequencing of the 16S rRNA gene fragments revealed microorganisms of the class Gammaproteobacteria, order Methylococcales. Since the share of methanotrophs was high at the sites of constant gas seepage (up to 1.93% of the total read number), they could be detected by sequencing of the native samples. Phylogenetic diversity of methane-oxidizing bacteria was not high, and all detected microorganisms belonged to the Deep-Sea 1 cluster. On the phylogenetic tree, the sequences formed a cluster together with the genus Methyloprofundus. Members of the genera Methylomonas and Methylobacter related to methanotrophs inhabiting freshwater ecosystems were revealed in enrichments from the coastal stations sediment samples. [ABSTRACT FROM AUTHOR]

The taxonomic diversity and metabolic activity of microbial communities in the Laptev Sea water column above and outside the methane seep field were studied. The concentrations of dissolved methane in the water column at both stations were comparable until the depth of the pycnocline (25 m). At this depth, local methane maxima were recorded, with the highest concentration (116 nM CH4) found at the station outside the methane seep field. Results of the 16S rRNA gene sequencing and measurements of the rates of hydrogenotrophic methanogenesis indicated the absence of methanogenesis caused by the methanogenic archaea in the pycnocline and in other horizons of the water column. The 16S rRNA-based analysis of microbial phylogenetic diversity, as well as radiotracer analysis of the rates of primary production (PP), dark CO2 assimilation (DCA), and methane oxidation (MO), indicated the functioning of a diverse community of pelagic microorganisms capable of transforming a wide range of organic compounds under oligotrophic conditions of the Arctic basin. Hydrochemical prerequisites and possible microbial agents of aerobic methane production via demethylation of methylphosphonate and decomposition of dimethylsulfoniopropionate using dissolved organic matter synthesized in the PP, DCA, and MO processes are discussed. [ABSTRACT FROM AUTHOR]

The use of X-ray microtomography, neutron tomography, scanning electron microscopy and X‑ray microanalysis in the study of stromatolites is discussed, and the advantages of each of these methods are summarized. Scanning electron microscopy allows study of the morphology of the object surface. Information about the composition and ratio of chemical elements of surface structures can be obtained using X‑ray microanalysis. X-ray microtomography will be useful for detecting internal structures and their localization in the sample. Neutron tomography can be used to search for organic matter and other hydrogen-containing compounds. [ABSTRACT FROM AUTHOR]

Soda lakes are relic ecosystems inhabited by unique microorganisms, which are doubly extremophilic: both haloalkaliphilic and natronophilic. Two morphologically and physiologically similar monocultures of filamentous anoxygenic phototrophic bacteria (FAPB) were isolated from the water samples and biofilms on plants of the coastal zones of the steppe soda lakes Tanatar 6 and Gorchina 1 (Kulunda, Altai krai) during the season of their desalination. In their natural environments, FAPB coexisted with anoxygenic purple sulfur bacteria of the genera Chromatium,Thiocapsa, Ectothiorhodospira, and Thiorhodospira, as well as with oxygenic phototrophs (alkaliphilic cyanobacteria, euglenophytes, and diatoms). FAPB formed filaments surrounded by thin sheaths; their cells contained antenna structures (chlorosomes). Apart from small amounts of bacteriochlorophyll (BChl) a in the reaction center, both isolates contained also antenna BChl c and BChl d. Alpha- and beta-carotenes and their derivatives were also detected. FAPB grew well in the medium containing Na2S ∙ 9H2O (500 mg/L) at total mineralization of 15−30 g/L and pH 8−9.5. Identification of both cultures based on amino acid composition of the PufLM complex revealed that they belonged to the phylum Chloroflexi and were almost 100% identical both to each other and to the halo-alkaliphilic isolate "Candidatus Viridilinea mediisalina" Kir15-3F revealed previously in the Kiran soda lake (Eastern Siberia, Russia). It may be concluded that "Cand. Viridilinea mediisalina" is a typical component of Siberian soda lakes with moderate salinity. [ABSTRACT FROM AUTHOR]

Analysis of the taxonomic structure of prokaryotic microbial complexes of the saline soils in the Lake Elton area and their comparative characteristics were carried out for a soil catena along the Khara River flowing into the hypersaline Lake Elton. High-throughput pyrosequencing detected 11 bacterial and 2 archaeal phyla. Comparative analysis of community structure revealed the differences between Solonchaks located at the river flood land and Kastanozems at the slope and top of the river terrace. The patterns of occurrence were described for six predominant phyla (Euryarchaeota, Thaumarchaeota, Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria). For the floodplain soils, the relations between the distribution of Euryarchaeota, Thaumarchaeota, Firmicutes, Actinobacteria, Proteobacteria and soil salinity as well as soil pH were described. Occurrence of members of the phyla Euryarchaeota, Thaumarchaeota, Firmicutes, Actinobacteria, and Proteobacteria in flood land soils was shown to depend on the soil salinity and pH. Members of the phyla Actinobacteria and Firmicutes were shown to predominate in Gleyic Kastanozems. Cloning of the 16S rRNA gene revealed high diversity within the genus Streptomyces (Actinobacteria). A number of the isolated streptomycete clones were homologous to the known antibiotic producers, which indicates that soils of this area are promising for further biotechnological screening. [ABSTRACT FROM AUTHOR]

Abstract: Microstructures of silicic rocks shaped by the activity of thermophilic bacterial communities in active volcanism areas of Kamchatka are described in the present article. The role of microorganisms as a special matrix that accelerates the formation of microlayered rocks of mixed chemogenic and biogenic origin is demonstrated. The authors suggest the term "biosilicites" for such rocks. [ABSTRACT FROM AUTHOR]

Abstract: The modern soda lakes as relict biotopes, the analogs of which could be widespread in the Precambrian Era, are considered in the context of two hypotheses: "soda ocean" and "soda continent." The diversity of modern halophilic and alkaliphilic cyanobacteria has been analyzed in order to reveal the morphological forms which have paleo-analogs that could be used as indicators of soda conditions in the Precambrian. [ABSTRACT FROM AUTHOR]

Abstract—: The structure of microbial mats from the Mramornaya Bay (Crimea) was investigated. Light microscopy in combination with transmission and scanning electron microscopy revealed the base of bacterial mats to be interwoven thin filaments (100 to 500 nm in diameter) consisting mainly of sulfur. Numerous bean-shaped single microbial cells (~1.6 × 0.7 µm), some of which were attached to sulfur filaments, were also revealed. High-throughput sequencing of the 16S rRNA genes revealed predominance of bacteria of the genera Arcobacter (27%), Alcaligenes (17%), and Desulfuromonas (8.5%) as well as of uncultured members of the family Lachnospiraceae (4.9%). No clearly predominant microbial taxa were revealed in the detritus sample below the mats. Similar to the bacterial mat, bacteria of the genera Arcobacter and Desulfuromonas were predominant in the detritus, but their relative abundance was significantly lower (4.1 and 6%, respectively). Analysis of the 16S rRNA gene sequences specific for the genus Arcobacter revealed considerable phylogenetic diversity of this group in the samples from both the upper bacterial mats and the detritus sediment. Most of obtained sequences formed common clusters with the sequences of various uncultured members of the genus Arcobacter, while an insignificant share of them was related to the recently described sulfide-oxidizing bacterium “Candidatus Arcobacter sulfidicus.” Thus, members of the phylogenetically heterogeneous group of epsilonproteobacteria of the genus Arcobacter were the dominant component of the Mramornaya Bay microbial communities. [ABSTRACT FROM AUTHOR]

Clone libraries and morphological analysis were used to investigate cyanobacterial diversity in the cyanobacterial mat and dry crust at the bottom of the shallow, saline, alkaline Lake Khilganta (Southern Siberia, Russia). Filamentous cyanobacteria belonging to Phormidium genus and Coleofasciculus chthonoplastes were found to predominate during the dry period (2006) and the wet periods (1995 and 2012), respectively. Community composition during the dry and wet periods differed significantly. While 11 operational taxonomic units of cyanobacteria were revealed, only 3 occurred during both dry and wet periods. Occurrence of cosmopolitan C. chthonoplastes, which is common in neutral saline environments, is not typical of a continental alkaline lake and may be explained by the similarity of the dominant ions composition in lake water and in seawater. [ABSTRACT FROM AUTHOR]

Laboratory simulation of fossilization of cyanobacterial cells in the high-carbonate medium in the presence of calcium was carried out for the haloalkaliphilic natronophilic cyanobacterium 'Euhalothece natronophila' Z-M001. This organism was isolated from the Magadi soda lake, where the bioherms consisting of mineralized coccoid cyanobacteria were found in the Quaternary sediments. The structural and chemical heterogeneity of the minerals produced during this process was established, with calcium carbonate and trona being the main products. The differences in the process of cyanobacterial cell carbonatization in soda lakes and marine or freshwater systems were determined. Initial precipitation of calcium carbonate was shown to occur due to a chemical reaction not involving cyanobacteria. At the subsequent stages, amorphous CaCO is sorbed and crystallized on the surface of some of the cells within a cyanobacterial population, resulting in formation of a shell-like mineral layer. The cells embedded in trona in the same system were shown to undergo deformation and destruction. In both cases the mineralized cells were shown to lose their photosynthetic activity. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S0026261721110011 [ABSTRACT FROM AUTHOR]