Oxygen limitation is a pitfall during screening for industrial strains

Oxygen supply is a key parameter in aerobic fermentation processes like the industrial production of amino acids. Although the oxygen transfer rate (OTR; or the volumetric oxygen transfer coefficient k_La) is routinely analyzed by engineers during stirred tank fermentations, it is often not taken into account by biologists conducting screening experiments in shake flasks. To show the importance of knowing how to avoid oxygen transfer limitations during primary screenings, Corynebacterium glutamicum ATCC 13032 (wild-type strain) and DSM 12866 (lysine-producing strain) were cultivated in shake flasks with different culture liquid volumes and under different shaking conditions. With the Respiration Activity Monitoring System, the OTR was determined quasi-continuously. Optical density as well as concentrations of lysine and byproducts (lactate, acetate, succinate) were determined off-line and correlated with the OTR signal. From the results, design criteria for improved screening in shaken bioreactors that help to avoid selection of suboptimal strains during early process development steps can be derived. Finally, the suitability of DSM 12866 as a strain for industrial processes with a high space–time yield is discussed.