RESUMO
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 Bacillus subtilis BZR 336 g and Bacillus subtilis BZR 517 strains at various pH and temperature levels. In the experiment for determining the optimal temperature, the maximum titer of B. subtilis BZR 336 g bacterium (1.6-1.7 × 109 CFU/ml) was recorded at a cultivation temperature of 20-25 °C. For B. subtilis 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 B. subtilis BZR 336 g strain against the test culture of Fusarium oxysporum var. orthoceras was observed at a cultivation temperature of 20-25 °C; for B. subtilis BZR 517 strain, 25-30 °C. When determining the optimal pH level, it was found that a high titer of B. subtilis BZR 336 g strain cells was determined at pH 8.0 (2.7 × 109 CFU/ml), for B. subtilis 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 Fusarium pathogens.
