An improved high cell density cultivation-iHCDC-strategy for leucine auxotrophic Escherichia coli K12 ER2507

Fed-batch processes are commonly used tools in high cell density cultivation of Escherichia coli. However, the setup of a fed-batch process can be challenging, especially when working with genetically modified strains. This work deals with the design of a specific strategy for the leucine auxotrophic E. coli strain K12 ER2507 that is of interest for arabinose-inducible gene expression systems due to its ara-14 mutation. To set up this process the optimum yield coefficient of biomass from leucine was determined by use of a design of experiments tool. Unfortunately, the yield coefficient is negatively influenced by both leucine and glucose concentrations. Furthermore, an inhibitory effect of leucine reduced the specific growth rate even at low concentration. Under consideration of these problems, an improved high cell density cultivation (iHCDC) for E. coli K12 ER2507 was established. The start medium was set up without any C-source to omit a batch phase with high glucose concentration and substrate feeding was initiated directly upon inoculation. Due to the poor solubility of leucine in feed medium, the amino acid was dissolved in the base. With the improved high cell density cultivation process a final cell density of more than 90 g/L was obtained reproducibly.