Natalia S. Zhemchuzhina

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 wide species diversity of chitinolytic actinomycetes producing secondary metabolites and hydrolytic enzymes offers opportunities for effective soil biocontrol aimed at protecting plants from phytopathogens and preserving soil biodiversity. This study examined the chitinolytic potential of five soil actinomycete strains from the genus Streptomyces(S. flavovirens TT, S. sindenensis TK, S. baarnensis assi-23TB, S. anulatus TG, and S. xiamenensis TB) through integrated analytical and molecular biological approaches.The study demonstrated that the fundamental mechanism of Streptomycesstrain adaptation to chitin utilization is the targeted induction of functional chitinase genes.We identified distinct genome activation strategies and observed that high genetic activity leads to a robust physiological response, including active biomass accumulation and CO₂ emission. These findings confirm the high competitiveness of the investigated strains under conditions of limited access to readily available carbon and nitrogen sources. The study elucidated the interaction of the target strain Streptomyces baarnensis assi-23TB (VKPM Ac-2228) with two specific phytopathogens in both in vitro and in planta systems, using wheat seedlings (Triticum aestivum L. cv. Arkhat) and microclonal potato plants (Solanum tuberosum L. cv. Romano) as host models. A comparative analysis was performed to correlate the metabolic capabilities of S. baarnensis assi-23TB, as theoretically predicted by bioinformatic tools (antiSMASH, PATRIC), with its actual phenotypic metabolite production. The strain exhibited significant chitinolytic activity. Our analysis revealed dibutyl phthalate (DBP) to be a constitutive secondary metabolite responsible for the baseline antimicrobial activity.Notably, several predicted biosynthetic gene clusters (10-epi-HSAF, keivymicin, alkylresorcinol, desferrioxamine B, naringenin, and zeatin) remained in a "silent" state under the experimental conditions. We found that the S. baarnensis exometabolome strictly depends on the presence of the host plant and specific pathogens (Fusarium graminearum and Phytophthora infestans). The association with wheat exclusively triggers the synthesis of the phytostimulant putrescine and energy metabolism regulators, such as lactic and succinic acids. This symbiotic system also drives the production of amino acids, sugars, and myo-inositol.The study experimentally confirms the multifunctionality of the Streptomyces baarnensis assi-23TB strain, which integrates direct enzymatic lysis of pathogens with the biochemical stimulation of plant growth and adaptive responses