## 3 Results and Discussion
### Antibacterial and Antifungal Activity of Bacillus amyloliquefaciens \(\mathrm{M}\)
Due to its high maximum specific growth rate, the time to reach the maximum productivity of vegetative cells was short \(\tau_{ex}=16.2\) h.  
Figure 5: Changes in the concentration of vegetative cells and spores during batch cultivation of _Bacillus amyloliquefaciens_ M in a laboratory bioreactor with stirring. Most likely, after this time, the sporulation process began, since at the 24 th h, the amount of spores was of the magnitude order of \(10^{7}\) cfu/cm\({}^{3}\). The monitoring of the total active cell concentration was therefore stopped and determination of the number of spores only began. An important parameter for biopreparation production is the sporulation rate because it determines the process duration. The sporulation rate for the studied strain was high \(\mu_{m5}\) = 0.451 h\({}^{-1}\), resulting in a high spore concentration at the end of the process--around \(10^{12}\) spores/cm\({}^{3}\). The percentage of sporulation was calculated according to a modified equation [42]:  
\[\%\ of\ sporulation=\frac{number\ of\ spores}{total\ number\ of\ cells}\times 100\]  
A high sporulation rate of 86% was observed as early as the 48 th h from the start of the cultivation process of _Bacillus amyloliquefaciens_ M, confirming the high concentration of spores at the end of the cultivation. For practice, the time to reach this percentage of sporulation is of great interest, and it is calculated by the equation for \(\tau_{\mathrm{es}}\) (Equation (2)). An 86% sporulation percentage in this strain would be reached at the 24 th h of cultivation, after initiation of sporulation. A comparison of the experimental data with those obtained from the models was made (Figure 6). The mathematical models agreed well with the experimental data (Figure 6). Both models describe the experimental data very well, as a result of which they can be used to control and predict the fermentation process carried out with _Bacillus amyloliquefaciens_ M, which has also been found for other _Bacillus amyloliquefaciens_ strains [41]. The results obtained for spore formation in _Bacillus amyloliquefaciens_ M were better compared to those obtained by [PERSON], 2008 [42] for _Bacillus amyloliquefaciens_ strain B 128 (5.93 \(\times\) 10\({}^{8}\) spores/cm\({}^{3}\), after the 48 th h) and [PERSON], 2015 [43], which achieved 88.7% sporulation at the 66 th h. Figure 7 shows the changes in the redox potential during cultivation. Figure 6: Comparison of experimental data with the logistic curve model and the exponential spore formation model (1). During intensive growth, the redox potential decreased until the culture entered into the stationary growth phase, when its value was retained (Figure 7). The redox potential started to increase when the sporulation of the strain began, which was explained by the lower intensity of respiration by the population. A similar trend was observed in the concentration of dissolved oxygen. During the exponential phase, the dissolved oxygen concentration dropped to 0, indicating a large rate of oxygen consumption and very high respiratory activity. At the start of sporulation, the concentration of dissolved oxygen increased and remained relatively constant--between 8% and 10% until the end of the process. This was due to the reduction in the number of vegetative cells, which reduced the respiratory activity of the population as a whole. The pH slightly decreased during the lag phase, after which it started to steadily increase (Figure 8). A relatively constant pH value between 8.43 and 8.33 was established when the sporulation process began. Thus, a concentrate (10\({}^{12}\) spores/cm\({}^{3}\)) of _Bacillus amyloliquefaciens_ M with high antibacterial and antifungal activity was obtained. Figure 8: Dynamics of pH change during batch cultivation of _Bacillus amyloliquefaciens_ M in a laboratory bioreactor with stirring. Figure 7: Dynamics of changes in the redox potential at dissolved oxygen concentration of 45%.