2. DO-stat fed-batch fermentation
We conducted DO-stat fed-batch fermentation to increase the yield of β-carotene (Figure 2). Glucose (1350 g) was used to maintain DO value at 10%-20%. The medium for the fed-batch phase contained 8 g/L glucose, which was depleted completely after 20 h. DO-stat fed-batch fermentation was implemented at this time until the end of fermentation. The increase of biomass tended to be stable after 96 h fermentation, which demonstrates the cell growth entered the stationary period. 94 g/L biomass and 0.4 g/L β-carotene concentration were harvested at the end of DO-stat fed-batch fermentation, separately. 8 g ammonium sulfate was fed at 24th, 48th, and 72th h to avoid pH rise.
Application of DO-stat fed-batch fermentation resulted in a 1.3-fold higher production of biomass and β-carotene content when compared to fed-batch fermentation. More glucose were consumed in DO-stat fed-batch fermentation.
3.More ATP and NADP+/NADPH were produced in DO-stat fed-batch fermentation
The intracellular levels of ATP content and NADP+/NADPH were determined to explore the effect of feeding strategy on the generation of energy ATPs and NADP+/NADPH.
ATP was gradually diminished during fed-batch fermentation. The highest level of ATP appeared at 24th h (Figure 3). At the 48th h, the ATP content was dropped to 0.81 nM/mg protein. The ATP content was only 0.43 nM/mg protein at the 72nd h.
More ATP were generated in the DO-stat strategy when compared to the fed-batch strategy. The ATP content was 6.80 nM/mg protein at 24th h during DO-stat fed-batch fermentation. ATP content gradually decreased as the fermentation progresses and dropped to 2.33 nM/mg protein at the 72nd h.
More NADP+/NADPH was generated during the fed-batch fermentation (Figure 4). NADP+/NADPH content was the least at 24th h in fed-batch fermentation. At 48th h, the NADP+/NADPH content reached 15.29 nM/mg protein. The NADP+/NADPH content was 17.49 nM/mg protein at 72nd of fed-batch fermentation.
More NADP+/NADPH were generated in DO-stat fermentation when compared to fed-batch fermentation. NADP+/NADPH content was least at 24th h. NADP+/NADPH content was increased to 52.86 nM/mg protein at the 48th h. NADP+/NADPH content reached 101.36 nM/mg protein at the the 72nd h during DO-stat fed-batch fermentation.