Regarding the stirred-tank bioreactors used in that study (based on the same working principle as those used during the experiments described in our paper) the maximal level of 1,3-PD, 56 g/L, was observed in the 30 L bioreactor. However, Günzel et al. [24] did not use crude but pure glycerol as a carbon source. Papanikolaou et al. [36] studied 1,3-PD synthesis from glycerol by C. butyricum F2b in batch fermentation and received a final 1,3-PD concentration of 47.1 g/L from 65 percent pure glycerol. The yield of the process was 0.53 g/g, equal to that achieved in the present work. Anand and Saxena [37] while testing Citrobacter

freundii obtained a yield level of 0.51 g/g for 1,3-PD synthesis from crude glycerol and a final 1,3-PD concentration of 25.6 g/L. Fed-batch fermentation The batch fermentations were carried out CDK activation to check whether the optimization of the cultivation medium and the

fermentation buy Ivacaftor tests were properly conducted on a laboratory scale [38]. The purpose of the fed-batch fermentations was to achieve an increased production of 1,3-PD. This method enables the use of high glycerol amounts and allows for the reduction of stresses resulting from the high osmolality of production media [30]. The kinetics of 1,3-PD production in fed-batch fermentation was compared between the 6.6 L and the 150 L bioreactors (Figure 1 and Figure 2). The concentration of glycerol at the start of fermentation was 50 g/L. The highest concentration of 1,3-PD, 71 g/L, was obtained in the 6.6 L bioreactor from 132 g/L glycerol (Figure 1a). In the 150 L bioreactor Unoprostone the final product concentration did not exceed 60 g/L (Figure 2a). Figure 1 Kinetics of glycerol consumption (filled circles) and 1,3-propanediol production (filled squares) (a); butyric acid (open circles), lactic acid (open squares), acetic acid (open triangles), ethanol (cross), production and biomass growth (stars) (b) during growth of C. butyricum DSP1 in fed-batch in 6.6 L bioreactor experiments. Figure 2 Kinetics

of glycerol consumption (filled circles) and 1,3-propanodiol production (filled squares) (a); butyric acid (open circles), lactic acid (open squares), acetic acid (open triangles), ethanol (cross), production and biomass growth (stars) (b) during growth of C. butyricum DSP1 in fed-batch in 150 L bioreactor experiments. In the beginning the basic kinetic parameters of batch and fed-batch fermentations were comparable, with the only difference in the length of the adaptive phase of bacteria growth. As a result, the stationary phase started as early as 5 hours after inoculation of the fermentation medium. However, the rate of 1,3-PD production significantly decreased after adding the second portion of glycerol and biomass growth was no longer observed. It has been reported that biological processes occurring on a large scale are limited by environmental stresses [22].