Background: Heterologous production of natural products in Escherichia coli has emerged as an attractive strategy\nto obtain molecules of interest. Although technically feasible most of them are still constrained to laboratory scale\nproduction. Therefore, it is necessary to develop reasonable scale-up strategies for bioprocesses aiming at the overproduction\nof targeted natural products under industrial scale conditions. To this end, we used the production of the\nantibiotic valinomycin in E. coli as a model system for scalable bioprocess development based on consistent fed-batch\ncultivations.\nResults: In this work, the glucose limited fed-batch strategy based on pure mineral salt medium was used throughout\nall scales for valinomycin production. The optimal glucose feed rate was initially detected by the use of a bio catalytically\ncontrolled glucose release (EnBaseÃ?® technology) in parallel cultivations in 24-well plates with continuous\nmonitoring of pH and dissolved oxygen. These results were confirmed in shake flasks, where the accumulation of\nvalinomycin was highest when the specific growth rate decreased below 0.1 hâË?â??1. This correlation was also observed\nfor high cell density fed-batch cultivations in a lab-scale bioreactor. The bioreactor fermentation produced valinomycin\nwith titers of more than 2 mg LâË?â??1 based on the feeding of a concentrated glucose solution. Valinomycin production\nwas not affected by oscillating conditions (i.e. glucose and oxygen) in a scale-down two-compartment reactor,\nwhich could mimic similar situations in industrial bioreactors, suggesting that the process is very robust and a scaling\nof the process to a larger industrial scale appears a realistic scenario.\nConclusions: Valinomycin production was scaled up from mL volumes to 10 L with consistent use of the fed-batch\ntechnology. This work presents a robust and reliable approach for scalable bioprocess development and represents\nan example for the consistent development of a process for a heterologously expressed natural product towards the\nindustrial scale.
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