POLYENE ANTIBIOTICS AND GROWTH REGULATING SUBSTANCES BIOSYNTHESIS BY STREPTOMYCES NETROPSIS IMV AC-5025 UNDER THE ACTION OF EXOGENOUS Β-SITOSTEROL
Loboda M, Biliavska L.
D.K. Zabolotny Institute of Microbiology and Virology of the NAS of Ukraine,
Department of general and soil microbiology
Actinobacteria of Streptomyces genus are active producers of a wide spectrum of biologically active metabolites that determines the regulation of plant growth and induction of the resistance against stress factors, provide antagonism against phytopathogens. The strain Streptomyces netropsis IMV Ac-5025 was isolated by the researchers from the Institute of Microbiology and Virology, NAS of Ukraine. It produces a wide spectrum of biological metabolites, such as polyene antibiotics, phytohormones, lipids (phospholipids, sterols), etc. Steroid compounds play an important role in the vital activity of cells serving as structural elements of biological membranes; also they have an adaptation role. The aim of the work was to research the effect of exogenous β-sitosterol on the polyene antibiotics and abscisic acid (ABA) biosynthesis by S. netropsis IMV Ac-5025.
The strain was cultivated using in-depth method іn synthetic and organic nutrient media and stored in oaten (ISP-3) agar at +4°C. Concentrations of exogenous β-sitosterol were 0.1, 0.25, 2.5, 5.0, and 10 μg/mL. In the stationary phase of growth we measured the biomass accumulation and detected the polyene antibiotics and abcisic acid biosynthesis in it. Biomass was taken into account by the gravimetric method and expressed in grams of absolutely dry biomass (ADB) per 1 liter of nutrient medium. The content of polyene antibiotic and phytohormone was determined in culture liquid and ethanolic extracts of biomass by thin layer spectrodensitometric chromatography method. Under the action of 5 μg/mL of exogenous β-sitosterol in synthetic nutrient medium, the amount of biomass was increased in 1.96 times, in organic – in 1.4 times (the quantity was 5.2 g ADB and 10.2 g ADB, respectively). Among the metabolites of tested strain, two fractions of polyene macrolides were identified: heptaene candidine and a new tetraene compound. The biosynthesis of both compounds was increased under the action of exogenous β-sitosterol. In the synthetic nutrient medium in the culture liquid under the action of 5 μg/mL of the substance, the amount of candidine was increased in 2.2 times, tetraene – in 1.4 times, the sum of polyene antibiotics in 2 times. In the biomass extract the amount of candidine was increased in 1.5 times, tetraene in 3.1 times, the sum in 1.7 times. In an organic nutrient medium in the culture liquid under the aсtion of 5 μg/mL of exogenous β-sitosterol the amount of candidine was increased in 2 times, tetraene – in 1.2 times, the sum of polyene antibiotics – in 1.8 times. In the biomass extract, the largest amount of antibiotics was identified under the action of 10 μg/mL of exogenous substance: the amount of candidine was increased in 2.5 times, tetraene in 3 times, the sum of polyenes – in 2.7 times. The ability of the strain to accumulate in cells antistress phytohormone-abscisic acid was detected. ABA plays an important role in the adaptation of streptomycetes to adverse external factors. Being formed in the air hyphae and spores, it helps to minimize the loss of water through the membrane into the air. Under the action of exogenous substances the amount of phytohormone in the biomass was increased and reached the highest values under the action of 10 μg/mL of exogenous β-sitosterol in both nutrient media.
The results of the work are fundamental for understanding the possible interrelationships in the biosynthesis of biologically active substances by soil streptomycetes. Increasing of the biosynthesis of polyene antibiotics and ABA in streptomycetes cells may be associated with stress and adaptive survival strategy in adverse conditions.