Lyudmila Vyacheslavovna Lysak

Complexes of cultured saprotrophic bacteria and yeasts from different components of soil constructions (humus soil horizon and peat) were studied simultaneously with the assessment of auxin-producing activity (synthesis of 3-indolylacetic acid, IAA), of some bacteria and yeast strains isolated. The study was conducted at the stage of laying two variants of constructions in Syktyvkar, formed from components of local origin (variant 1) and imported (humus soil horizon, Moscow, peat "Seliger-agro", Tver region) (variant 2).

The taxonomic structure of microbial complexes isolated from the studied substrates had significant features of similarity. At the same time, components of variant 1 revealed a greater diversity of cultivated saprotrophic bacteria (Bacillus species) species resistant to adverse environmental conditions as well as the presence of psychrophilic basidiomycete yeast Leucosporidium scottii, which was not found in the components of variant 2.

The average IAA production by the yeast strains studied was 647.6 µg/L and by saprotrophic bacteria - 741.3 µg/L. The highest values of IAA concentration were found in the culture liquid of the yeast Tausonia pullulans (strain Y-6) - 3362.6 µg/l, isolated from the humus soil layer of variant 1, and of the two saprotrophic bacteria Flavobacterium рsychrophilum (strain B-7 - 2616.8 µg/L and B-5 - 1056.3 µg/L), isolated from the humus soil horizon in variant 1 and from peat of variant 2. For strains of the yeast Leucosporidium scottii and the cultured saprotrophic bacteria Flavobacterium psychrophilum the ability to synthesize IAA was found for the first time. 

A comprehensive study of prokaryotic communities (microbiomes) of bacterial mats and snottites from the karst cave Sheki-Kh’ekh was carried out for the first time, with comparison to cave soil-like bodies (SLBs) from the Muhammed-Kh’ekh cave and adjacent brown forest soil. The total abundance of bacterial cells in mats and snottites varied within a relatively narrow range, from 0.26 to 0.35 billion cells per mL, reaching maximum values in floating bacterial mats and minimum values in snottites. In soil-like bodies, the total bacterial abundance was 0.28 billion cells per g. Actinomycete mycelium was detected in all cave samples, with the highest values observed in floating bacterial mats and the lowest in shoreline bacterial mats.
Metabarcoding analysis (16S rRNA gene sequencing) revealed high taxonomic diversity of prokaryotic communities across the studied substrates. The greatest diversity was recorded in floating bacterial mats (25 phyla and 74 genera). In all cave substrates, the dominant phyla were Pseudomonadota and Bacillota, while Bacteroidota also dominated in floating bacterial mats. Lower relative abundances were observed for Actinomycetota, Verrucomicrobiota, Chloroflexota, Chlorobiota, and Thermodesulfobacteriota. Eleven bacterial phyla were shared between soil and floating bacterial mats: Pseudomonadota,Bacillota,Bacteroidota,Verrucomicrobiota,Chlorobiota,Chloroflexota,Actinomycetota,Acidobacteriota,Cyanobacteriota,Planctomycetota, and Armatimonadota, along with two candidate phyla, Sumerlaeota and Hydrogenedentes. Two archaeal phyla, Woesearchaeota and Nanoarchaeota, were detected in bacterial mats.
A total of 191 bacterial genera were identified across all studied substrates. Only 12 genera were common to bacterial mats and soil: Brevundimonas,Devosia, Flavobacterium,Luteolibacter, Paenibacillus,Paenisporosarcina,Pseudarthrobacter, Pseudomonas,Rhodanobacter,Sphingomonas, Sumerlaea, and Thermomonas. A distinctive feature of floating bacterial mat communities was the high representation of genera involved in sulfur cycling processes. Functional profiling revealed the predominance of sulfur- and iron-cycle-related functions in bacterial mats, whereas nitrogen-cycle-related functions and chemoheterotrophy prevailed in soil communities.
This study significantly expands current knowledge of the taxonomic composition of prokaryotic communities inhabiting bacterial mats and snottites of sulfidic caves in the Chechen Republic. The presence of bacterial genera involved in sulfur and iron transformation processes highlights their ecological significance. The results obtained on the diversity of prokaryotic communities in mats, snottites, and soil-like bodies are of interest for understanding ecosystem functioning and for the targeted search of strains with valuable biotechnological properties.

For the first time, a comprehensive study of the biological activity of microbial communities in protected tropical ecosystems of Vietnam has been conducted using the example of four types of substrates: mineral soils and associated plant litter, rhizospheric soil, and specific soil-like formations —“suspended” soils in baskets of epiphytic ferns. It is shown that suspended soils and plant litter are characterized by 3‒5 times higher microbial biomass (up to 1.44 mg•g⁻1), as well as significantly more intensive processes of carbon dioxide emission, nitrogen fixation and denitrification compared with mineral soil horizons. The revealed high biological activity of these substrates correlates with an extremely high content of organic carbon (up to 51.4%) and less acidic pH values. For the first time, methane emissions were quantified for this territory, showing maximum values in the upper soil layer (up to 173 ng CH4•g‒1•day–1) and a negative correlation with altitude (p=0.0001). The data obtained make it possible to identify plant litter and epiphytic “suspended” soils as key loci of biogeochemical cycles of nitrogen and carbon in the tropical forests of Vietnam.

Abstract.This study presents the findings of an investigation into the abundance and morphological diversity of bacteriophages in samples of urban soils (Urbanozem and Replantozem) and atmospheric dustfall (ADF) collected across Moscow from sites with varying degrees of anthropogenic impact. Using direct epifluorescence microscopy with the SYBR Gold stain, it was demonstrated that bacteriophage abundance (virus-like particles, VLPs) was higher in soils (1.12–2.1010⁹ VLPg‒1) than in ADF (0.42–0.6410⁹ VLPg‒1), correlating with total bacterial counts. Through enrichment culture techniques followed by biological purification, a collection of bacteriophages (coliphages) infecting Escherichia coli strains with different cell surface compositions (different O-antigen types) was obtained. Transmission electron microscopy revealed that some of the isolated coliphages belong to the class Caudoviricetes (tailed phages) and are characterized by Siphoviridae (possessing long, non-contractile tails) and Podoviridae (possessing short tails) morphotypes. The obtained data underscore the significant role of bacteriophages in the functioning of microbial communities within urban ecosystems and their potential for use in the bioremediation of urban soils.