Optimization of laboratory cultivation conditions for the synthesis of antifungal metabolites by bacillus subtilis strains

In order to achieve the optimal number of colony forming units and a high level of antifungal metabolites synthesis, we carried out the periodic cultivation of the <i>Bacillus subtilis</i> BZR 336 g and <i>Bacillus subtilis</i> BZR 517 strains at various pH and temperature levels. In the experiment for determining the optimal temperature, the maximum titer of <i>B. subtilis</i> BZR 336 g bacterium (1.6-1.7 × 10⁹ CFU/ml) was recorded at a cultivation temperature of 20-25 °C. For <i>B. subtilis</i> BZR 517 strain, the temperature turned out to be optimal at 30 °C: the titer was 8.9 × 10⁸ CFU/ml. The maximum antifungal activity of <i>B. subtilis</i> BZR 336 g strain against the test culture of <i>Fusarium oxysporum</i> var. <i>orthoceras</i> was observed at a cultivation temperature of 20-25 °C; for <i>B. subtilis</i> BZR 517 strain, 25-30 °C. When determining the optimal pH level, it was found that a high titer of <i>B. subtilis</i> BZR 336 g strain cells was determined at pH 8.0 (2.7 × 10⁹ CFU/ml), for <i>B. subtilis</i> BZR 517 strain it was at pH 6.0-8.0 (1.0 × 10⁹ CFU/ml). The maximum antifungal activity was noted with the same indicators. Chromatographic and bioautographic analyses suggest that the synthesized antifungal metabolites belong to surfactin and iturin A. The data obtained in this research can be used in the development of the technology for the production of effective biofungicides to protect crops against <i>Fusarium</i> pathogens.