Design-of-Experiment-Guided Establishment of a Fermentative Bioprocess for Biomass-Bound Astaxanthin with Corynebacterium glutamicum

Abstract

Corynebacterium glutamicum is prominent in the industrial production of secreted amino acids. Notably, it naturally accumulates the carotenoid pigment decaprenoxanthin in its membranes. Metabolic engineering enabled the production of astaxanthin. Here, a bioprocess for astaxanthin production in lab-scale stirred bioreactors was established by a DoE-guided approach to optimize the basic process parameters pH, rDOS, aeration rate as well as inoculation cell density. The DoE-guided approach to characterize 2 L scale cultivation revealed that the pH showed the strongest effect on the product formation. Subsequently, an optimum at pH 8, an aeration rate of 0.25 vvm, 30% rDOS and an initial optical density of 1 was established that allowed production of 7.6 ± 0.6 mg L−1 astaxanthin in batch mode. These process conditions were successfully transferred to a fed-batch process resulting in a high cell density cultivation with up to 60 g CDW L−1 biomass and 64 mg L−1 astaxanthin and thus demonstrating an about 9-fold improvement compared to optimal batch conditions. Moreover, pH-shift experiments indicate that the cells can quickly adapt to a change from pH 6 to 8 and start producing astaxanthin, showing the possibility of biphasic bioprocesses for astaxanthin production.