A study on the effects of increment and decrement repeated fed-batch feeding of glucose on the production of poly(3-hydroxybutyrate) [P(3HB)] by a newly engineered Cupriavidus necator NSDG-GG mutant in batch fill-and-draw fermentation

This study investigates the effect of strategies on poly(3-hydroxybutyrate) [P(3HB)] production in bioreactor. In the production of P(3HB), urea and glucose feeding streams were developed to characterize the fed-batch culture conditions for new Cupriavidus necator NSDG-GG mutant. Feeding urea in repeated fed-batch stage (RFB-I) at 6, and 12 h in cultivation led to insignificant kinetic effect on the cell dry mass (CDM) and P(3HB) accumulation. Feeding glucose in repeated fed-batch stage (RFB-II) demonstrated that the incremental feeding approach of glucose after urea in fill-and-draw (F/D) mode at 24, 30, 36, 42, and 48 h in fermentation increased CDM and P (3HB) concentration. In the 1st cycle in RFB-II, the cumulative CDM reached the value of 26.22 g/L and then it increased with the successive repeated fed-batches to attain biomass of 145 g/L at the end of 5th cycle of RFB-II. The final cumulative P(3HB) concentration at the end of 5th cycle of RFB-II reached 111 g/L with the overall yield of 0.50 g P(3HB) g gluc(-1); the CDM productivity from the RFB-II cycles was in the range of 0.84-1.3 g/(L.h). The RFB-II of glucose in an increment mode produced nearly 2.2 times more increase in CDM and P(3HB) productivities compared to the decrement RFB-II mode. Repeated cultivation had also the advantage of avoiding extra time required for innoculum preparation, and sterilization of bioreactor during batch, thereby it increased the overall industrial importance of the process.