Browsing by Person "Off, Manuel"

Now showing 1 - 2 of 2

The influence of growth rate-controlling feeding strategy on the surfactin production in Bacillus subtilis bioreactor processes
(2024) Hiller, Eric; Off, Manuel; Hermann, Alexander; Vahidinasab, Maliheh; Benatto Perino, Elvio Henrique; Lilge, Lars; Hausmann, Rudolf
Background The production of surfactin, an extracellular accumulating lipopeptide produced by various Bacillus species, is a well-known representative of microbial biosurfactant. However, only limited information is available on the correlation between the growth rate of the production strain, such as B. subtilis BMV9, and surfactin production. To understand the correlation between biomass formation over time and surfactin production, the availability of glucose as carbon source was considered as main point. In fed-batch bioreactor processes, the B. subtilis BMV9 was used, a strain well-suited for high cell density fermentation. By adjusting the exponential feeding rates, the growth rate of the surfactin-producing strain, was controlled. Results Using different growth rates in the range of 0.075 and 0.4 h-1, highest surfactin titres of 36 g/L were reached at 0.25 h-1 with production yields YP/S of 0.21 g/g and YP/X of 0.7 g/g, while growth rates lower than 0.2 h-1 resulted in insufficient and slowed biomass formation as well as surfactin production (YP/S of 0.11 g/g and YP/X of 0.47 g/g for 0.075 h-1). In contrast, feeding rates higher than 0.25 h-1 led to a stimulation of overflow metabolism, resulting in increased acetate formation of up to 3 g/L and an accumulation of glucose due to insufficient conversion, leading to production yields YP/S of 0.15 g/g and YP/X of 0.46 g/g for 0.4 h-1. Conclusions Overall, the parameter of adjusting exponential feeding rates have an important impact on the B. subtilis productivity in terms of surfactin production in fed-batch bioreactor processes. A growth rate of 0.25 h-1 allowed the highest surfactin production yield, while the total conversion of substrate to biomass remained constant at the different growth rates.
Model-based process design for surfactin production with Bacillus subtilis
(2025) Hiller, Eric; Off, Manuel; Dittmann, Holger; Perino, Elvio Henrique Benatto; Lilge, Lars; Hausmann, Rudolf; Hiller, Eric; Department of Bioprocess Engineering, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany; Off, Manuel; Department of Bioprocess Engineering, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany; Dittmann, Holger; Department of Bioprocess Engineering, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany; Perino, Elvio Henrique Benatto; Department of Bioprocess Engineering, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany; Lilge, Lars; Department of Bioprocess Engineering, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany; Hausmann, Rudolf; Department of Bioprocess Engineering, Institute of Food Science and Biotechnology, University of Hohenheim, Stuttgart, Germany
Bacillus subtilis is one of the most important production organisms in industrial biotechnology. However, there is still limited knowledge about the kinetics of fed-batch processes in bioreactors, as well as a lack of biological performance indicators, such as production yields, particularly regarding their variation over time. Understanding these kinetics and changes is crucial for optimizing the productivity in fed-batch processes. Fed-batch bioreactor cultures of Bacillus subtilis BMV9 in high cell density processes for surfactin production have been characterized with a kinetic model composed of first-order ordinary differential equations, describing the time course of biomass, substrate, surfactin and acetate. This model contributes to understanding critical restrictions and the knowledge gained was used to design and implement a model-based process. The model integrates biomass growth based on Monod kinetics, substrate consumption, surfactin synthesis and formation of the by-product acetate. After the model was parameterized for B. subtilis BMV9 using 12 different fed-batch bioreactor experiments, the kinetic model was able to accurately describe biomass accumulation, substrate consumption, product formation rates and, to some extent, the overflow metabolism involving acetate. Based on this, the kinetic model was used for a process design, in which the batch was omitted, which led to a product titre of 46.33 g/L and a space–time-yield of 2.11 g/(L*h) was achieved. The kinetic model developed in this study enables the description of the time course of biomass growth, substrate consumption and product formation and thus significantly improves process understanding. The computation of process parameters, which are not analytically accessible at any time, could be realized. A sensitivity analysis identified the maximum specific growth rate, substrate-related maintenance and the maximum acetate formation rate as key parameters influencing model outputs.