Cultivation was performed using the optimized chemically defined media formulation. During the exponential growth phase of the B. subtilis batch cultivation performed at 2-L bioreaction scale the agitation rate increased from 100 to approximately 1200 rpm to compensate for the oxygen consumption rate (Figure 3(a)). The results depicted in Figure 3(b) and Figure 3(c) show that the maximum vegetative cell concentration (1.3 × 1010 cells/mL) was obtained at the end of the exponential growth phase but after that a high cell lysis was observed and only 48% of the vegetative cells gave rise to heat resistant spores, the final spore concentration being 6.3 ×
109 spores/mL.