High cell density culture of baker's yeast FX‐2 based on pH‐stat coupling with respiratory quotient

Abstract

The high cell density culture of baker's yeast FX-2 was investigated in a 50 L(A) automatic bioreactor. Herein, it was found firstly that the Crabtree effect clearly existed in batch fermentation with higher glucose content, then the critical initial glucose content range (ࣘ2.00 g L −1 ) was reasonably ascertained to effectively avoid Crabtree effect. In the next fed-batch fermentations with different strategies, the second strategy (maintain ethanol concentration lower than 0.10% and pH around 4.80) was confirmed to be more beneficial to yeast growth than the first strategy (keep reducing sugar not more than 2.00 g L −1 and control steady Carbon/Nitrogen ratio 3.05:1.00). After that, one optimal control strategy (maintain pH around 4.80 and keep respiratory quotient in the range of 0.90-1.00) was constructed to further enhance cell yield. Under an optimal control strategy, four schemes with the aim of achieving pH-stat were compared, and yeast extract instead of other alkaline materials was selected as a better regulator. As a result, 148.37 g L −1 dry cell weight, 38.25 × 10 8 mL −1 living cells, and 8.24 g L −1 h −1 productivity were harvested, which respectively elevated 23.74%, 135.38%, and 24.47% compared to that obtained under the traditional scheme (regulate pH with ammonia); meanwhile, the maximum oxygen uptake rate and carbon dioxide excretion rate were both more than 250.00 mmol L −1 min −1 .

Dissolved-oxygen feedback control fermentation for enhancing β-carotene in engineered Yarrowia lipolytica

“…Excessive alcohols and acids compete with β-carotene synthesis for the substrate of acetyl-CoA. The Crabtree effect eventually leads to a reduction in the yield of the target product 20 . Fed-batch cultures provide a carbon source at a low level by feeding essential nutrients incrementally 21 .…”

“…Therefore, this culturing technique is used to overcome the Crabtree effect 22 . Fed-batch strategies include constant dissolved oxygen value feeding (DO-stat) 23 – 27 , constant specific growth rate feeding (μ-stat) 25 , 28 , constant pH feeding (pH–stat) 20 , 29 , 30 , and constant carbon source concentration feeding 31 . Besides the Crabtree effect, oxygen in short supply is another obstacle in aerobic culture.…”

“…growth rate feeding (μ-stat) 25,28 , constant pH feeding (pH-stat) 20,29,30 , and constant carbon source concentration feeding 31 . Besides the Crabtree effect, oxygen in short supply is another obstacle in aerobic culture.…”