We describe the actinomycete strain IMV-70 isolated from the soils of Kazakhstan, which produces potent antibiotics with high levels of antibacterial activity. After the research of its morphological, chemotaxonomic, and cultural characteristics, the strain with potential to be developed further as a novel class of antibiotics with chemotherapeutics potential was identified asStreptomycessp. IMV-70. In the process of fermentation, the strainStreptomycesspp. IMV-70 produces the antibiotic no. 70, which was isolated from the culture broth by extraction with organic solvents. Antibiotic compound no. 70 was purified and separated into individual components by HPLC, TLC, and column chromatography methods. The main component of the compound is the antibiotic 70-A, which was found to be identical to the peptolide etamycin A. Two other antibiotics 70-B and 70-C have never been described and therefore are new antibiotics. The physical-chemical and biological characteristics of these preparations were described and further researched. Determination of the optimal growth conditions to cultivate actinomycete-producer strain IMV-70 and development of methods to isolate, purify, and accumulate preparations of the new antibiotic no. 70 enable us to research further the potential of this new class of antibiotics.

A b s t r a c tThe general requirement for biologicals is that they must be insensitive to climate change and soil conditions, including soil physicochemical composition, fertility levels, and pH values. Actinomycetes isolated from extreme habitats are able to produce biologically active substances not only under neutral conditions but also in saline, alkaline and acidic environments, which determines their importance in the biopreparations, being developed for plant protection. This study is the first to report the Streptomyces sp. strain K-541 antibiosis against the causative agents of several cereal fungal infections under various environmental conditions and the identification of the antibiotic produced. Streptomyces sp. strain K-541 isolated from extreme ecosystems of Kazakhstan was cultured under neutral (pH 7.0) and alternative growth conditions at 25.0 g/l NaCl (pH 7.2) or 2.5 g/l Na 2 CO 3 (pH 8.0). Antifungal activity was determined in agar block diffusion experiments and under paired coincubation with phytopathogenic fungi Fusarium solani (Mart.) Sacc., F. oxysporum Schlecht., F. heterosporum Nees, F. sporotrichiella Sherb., Piricularia oryzae Cavara, Alternaria triticina Prasada & Prabhu, A. alternate (Fr.) Keissl., Bipolaris sorokiniana (Sacc.) Shoemaker, and Aspergillus niger van Tieghem. For antibiotic A-541 production, the strain was cultured on an orbital shaker (180-200 rpm) for 120 hours at 28 С. The antibiotic was extracted with organic solvents and analyzed using thin layer chromatography and spectrophotometry. The studies have shown high antifungal activity of K-541 against all the phytopathogens examined. After 72 hour incubation at 25 С the growth inhibition zones were 20-56 mm in diameter depending on growth conditions which simulated different ecological niches. In co-culturing the strain K-541 and the phytopathogenic fungi, the fungal colonies decreased 1.8-2.7 times in diameter indicating the possibility of K-541 introduction into soil biocenoses for biocontrol of cereal fungal pathogens. High inhibition of growth was also observed under saline (2 % NaCl) and alkaline (0.2 % Na 2 CO 3 ) conditions. The antibiotic produced by strain K-541 was classified as a member of polyene group, a subgroup of the hexaenes. So strain K-541 is recognized as promising for the development of a new biopreparation with fungicidal activity against causal agents of cereal fungal infections under different environmental conditions.

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