Scheme 1
The strategy for designed B. amyloliquefaciens to manipulate the carbon flux to 2,3-BD branch. To make the 2,3-BD branch gains a competitive advantage over the end products of pyruvate-deriving pathways (such as acetic acid, lactic acid and succinic acid), several strategies were developed to manipulate the carbon flux to 2,3-BD branch in a designed B. amyloliquefaciens. Firstly, extra copies of NADH/NAD+ regeneration system were introduced into B. amyloliquefaciens by co-overproduction of glycerol dehydrogenase and acetoin reductase. Subsequently, the transcriptional regulator ALsR under the control of a moderate promoter PbdhA was introduced into B. amyloliquefaciens. Finally, a three-stage dissolved oxygen control strategy were proposed based on analysis of the characteristic of 2,3-BD fermentation, and a two-stage pH control strategy were proposed based on different pH preferences of ACR for reduction and oxidation