Alexey Lvovich Stepanov

One hundred and fifty strains of streptomycetes were isolated from grey and dark grey forest soils, as well as from typical chernozem. The isolated strains were analyzed in Vitro for antimicrobial activity on nutrient media and in grey forest soil against twenty-three collection pathogenic test cultures of fungi and bacteria. Four biologically active isolates with a wide spectrum of action were identified and deposited in the All-Russian Collection of industrial microorganisms of the National Research Centre Kurchatov Institute. They were identified and deposited under the following numbers: Streptomyces xiamenensis TB ВКПМ Ас-2204, Streptomyces anulatus TG ВКПМ Ас-2203, Streptomyces sindenensis TK ВКПМ Ас-2205, Streptomyces flavovirens TT ВКПМ АС-2202. A study of the effect of pre-sowing treatment of wheat seeds by the 15-day cultural liquids of the strains S. xiamenensis TB ВКПМ Ac-2204, S. anulatus TG ВКПМ Ac-2203, S. sindenensis TK ВКПМ Ac-2205 on germination rates and infection with F. graminearum revealed that they inhibited the growth of a pathogenic fungus. Besides, they improved seed vigour and germination of wheat. The resulting strains of soil actinomycetes can be used in biotechnology with an aim to create the new bioinoculants when dealing with phytopathogenic bacteria and fungi. The strains can also be used for stimulating the plant growth, as well as for soil bioremediation in organic farming. Through the application of the HPLC method, specialized antimicrobial metabolites of monosporic strain suspensions were identified. The identified antibiotics are N-Butylbenzenesulfonamide, 1-(1H-Benzo[d]imidazol-2-yl)ethan-1-ol, 2-[(3S)-1-(Cyclohexylmethyl)-3-pyrrolidinyl]-1H-benzimidazole-5-carbonitrile, Cyclo(leucylprolyl), Cyclo(phenylalanyl-prolyl). The identified antiseptics are Cetrimonium and Carvone. The identified phytohormone is auxin indole-3-acetic acid (IAA). Observation of the dynamics of development of introduced actinobacteria under study in soil samples showed high activity of streptomycetes that use chitin. Analysis of the diversity of the prokaryotic complex of the studied soil samples with the application of the high-throughput sequencing of the conserved region of the 16S rRNA gene method revealed during the introduction of S. xiamenensis TB ВКПМ Ac-2204 that its controlling role in the microbial community is due to its antibiotic-forming activity.

The paper presents the results of assessing the eff ect of the degree of soil erodibility on the abundance and diversity of cultivated fungi and actinomycetes in diff erent seasons of the annual cycle. The objects of the study are sod—podzolic soils (Umbric Retisols (Abruptic)) of diff erent degrees of washout, located on the slope of the southeastern exposure (Moscow region, Solnechnogorsk district), used for a long time for the cultivation of agricultural crops. The indicators of microbial abundance were determined by the cup method, identifi cation was carried out on the basis of phenotypic characters. It is shown that the decline in physical and agrochemical parameters of the soil, which is a result of erosion processes, leads to a change in microbiological parameters. A decrease in the abundance and species diversity of fungi and actinomycetes was found with an increase in the degree of soil erosion. Significant diff erences were found in the taxonomic composition of microbial communities of non-eroded and washed away soils (the Sorensen species similarity coeffi cient does not exceed 0.42 for fungi and 0.30 for actinomycetes). Taxonomic units of mycelial microorganisms have been identifi ed. Among the fungi are representatives of the species Aspergillus, Cladosporium and Scopulariopsis, among the actinomycetes are Streptomyces malachitospinus, S. candidus and Micromonospora aurantiaca.

The paper evaluates the effect of erosion processes on the agrochemical and microbiological properties of the soil in different seasons of the annual cycle. The objects of the study are agro-gray soil of varying degrees of water erosion (uneroded, slightly and moderately eroded) and gray soil under woody forest plantations (south of the Moscow region). It was found that the content of alkaline hydrolyzable nitrogen, exchangeable potassium and mobile forms of phosphorus in the soil depended both on the degree of soil erosion and on seasonal fluctuations. Analysis of the chemical composition of soil organic matter showed that in the summer there was an increase in carboxylic, carbonyl and aromatic components, and in other periods – carbohydrate fractions. In the agro-gray soil, bacterial biomass stocks ranged from 27 to 96 kgha‒1, fungal biomass – from 10 to 357 kgha‒1, their dynamics were determined to a greater extent by the degree of washout and to a lesser extent by the season. With an increase in the degree of washing, both fungal and bacterial biomass decreased in the series unwashed>slightly washed>medium washed. Washed-away soils lost an average of 50% of bacterial and 59% of fungal biomass relative to non-washed soils. In the gray soil, bacterial biomass stocks varied seasonally from 43 to 107 kgha‒1, and fungal biomass from 171 to 621 kgha‒1. The gray soil under forest was superior in microbial pool to all variants of agro-gray soil, and was also characterized by a high content of mycelium, both actinomycete and fungal. In the studied soils, the level of potential respiration (SIR) exceeded the level of actual respiration (BR) by 2‒33 times. Microbial biomass reacted most actively to the introduction of glucose in the average washed soil in the spring and summer periods.

The article presents the results of the research of the prokaryotic complex associated with plants in blackalder-meadowsweeteutrophic swamp (Zapadnodvinskiy District, Tver Region). The phylloplane (leaves, stems), rhizoplane (roots), and rhizosphere soil of six plants, namely Calla palūstris L., Filipendula ulmaria (L.) Maxim., Carex cespitosa L., Urtica dioica L., Athyrium filix-femina (L.) Roth ex Mert.and Scirpus sylvaticus L., were analyzed. The abundance of unicellular and mycelial bacteria in plant and soil substrates was determined by luminescent microscopy and culture method. The taxonomic composition of cultured bacteria was assessed on the basis of phenotypic characteristics and the results of 16S rRNA nucleotide sequence analysis. It was found that the dimensionless universal characteristic of prokaryotic communities — the K index (the ratio of bacteria counts based on microscopy and culture data) —and the alpha diversity index (the Shannon index)— increase in the order phylloplan<rhizoplan< rhizosphere soil. Representatives of 4 phyla, 23 genera, and 63 species of cultivated bacteria, 27 of which are mycelial. were isolated and diagnosed from the analyzed substrates. It was determined that Carexmicroloci were characterized by maximum abundance and diversity of bacteria. Filipendulamicroloci are promising targets for the isolation of streptomycetes with antagonistic potential against phytopathogenic fungi that cause various diseases in agricultural plants. It was shown that rhizosphere soil under plants in blackalder-meadowsweeteutrophic swamps is a substrate for the isolation of bacteria of the genus Stenotrophomonas, which are used as effective bioinoculants to stimulate plant growth and as microbiological agents for biocontrol.

Actinomycetes are key functional group of soil microorganisms that play a critical role in organic matter decomposition and the regulation of biogeochemical cycles in tropical ecosystems. This study provides a comprehensive analysis of actinomycete community structure and the physiological traits of cultivable strains in soils and litter from two protected areas in Southern Vietnam: Bidoup and Cat Tien Nature Reserves. We combined culture-based and molecular approaches, including quantification of cultivable actinomycetes, assessment of strain tolerance to abiotic stresses, evaluation of enzymatic activities, and high-throughput 16S rRNA gene sequencing to determine the taxonomic composition of prokaryotic communities. Actinobacteria were found to be dominant across soils, with clear differences between soils and litter. Litter communities were relatively uniform across elevations, whereas soil communities displayed pronounced variation. Cultured Streptomyces strains exhibited broad stress tolerance and high enzymatic activity, underscoring their ecological significance in tropical soil functioning.