Improvements in PHB production by wild type Cupriavidus necator using different feeding strategies

NYGAARD D; YASHCHUK O; NOSEDA D; HERMIDA E

Simposio; 5th Euro BioMAT 2019 - European Symposium and Exhibition on Biomaterials and Related Areas; 2019

Polyhydroxyalkanoates (PHA), of which polyhydroxybutyrate (PHB) is the most abundant, are polymers of bacterial origin used for various applications in the medical, industrial and agricultural fields. In this work, we report, the medium optimization study in shaken flasks and large-scale production in stirred-tank bioreactor of PHB by wild type Cupriavidus necator. Variation in fermentation conditions has been explored to increase the yield of PHB. In order to address the selection of the main factors and optimize the culture medium, an experiment was designed based on the coupled response surface methodology, with a complete factorial design. A maximum PHB production of 4,6 g/l and biomass production of 6,5 g/l was obtained under optimized conditions. Polymer production was then scaled up to 6 l batch fermentation, where a significantly higher biomass of 15 g/l with a content of 9,85 g/l of PHB and a productivity of 0,13 g/(l.h) was obtained. Afterwards fed-batch strategy was performed applying a three-stage procedure. The first stage consisted of a batch culture to allow cell growth. In the second phase a fed-batch culture was carried out by feeding with fructose (600 g/L), which was regulated according to the concentration of dissolved oxygen in the culture, with a 70% cut-off. In these two stages the NH4OH served to regulate the pH and also allowed avoiding nitrogen limitation. The third stage consisted of a fed-batch culture with nitrogen limitation; the fructose feed was regulated according to the dissolved oxygen with 30-20% cut-off and the base was replaced by NaOH. The maximum biomass production was 35 g/l with a PHB content of 17,5 g/l. Finally a fed batch process operated with an exponential feeding strategy in the second phase led to a maximum biomass production of 52,1 g/l with a PHB content of 27 g/l and a volumetric productivity of 0,40 g/(l.h).