pH fluctuations imperil the robustness of C. glutamicum to short term oxygen limitation.

The presence of complex gradients for, e.g., nutrients, oxygen or pH in industrial scale fed batch processes are a major challenge for process performance. To consider such impact of scale-up during laboratory scale process development, scale-down bioreactor simulation, i.e. mimicking inhomogeneous conditions, became the method of choice. However, most scale-down studies simulate combined inhomogeneities of more than one parameter, so that the impact of the individual parameters remains unclear. The presented scale down study addresses this challenge by separating the influence of glucose, pH and oxygen fluctuations in terms of their specific impact in a well-established two compartment scale down device. This was carried out for an 1,5-diaminopentane production process using the industrial production host Corynebacterium glutamicum. Strikingly, oxygen depletion alone showed no effect on the process performance while changes of only one pH unit in acidic as well as alkaline direction reduced the biomass and product formation. Even more pronounced phenotypes up to -13% of μ and -39% of YX/S were observed, when an oscillatory acidic pH shift was combined with dissolved oxygen fluctuations. These losses are accompanied by a missing regulation of fermentative pathways. In conclusion, large-scale C. glutamicum processes seem to be most sensitive to pH variation.