Synergistic strategy for high-yield 2,3-butanediol and acetoin production in Bacillus licheniformis MW03 based on metabolic engineering

Bacillus licheniformis is an efficient platform for 2,3-butanediol (2,3-BD) and acetoin production due to its rapid glucose utilization rate and adaptability to industrial fermentation conditions. Here, we isolated the B. licheniformis strain MW03 with high yield of acetoin and 2,3-BD, which carried genetic mutations in acoR and budC, respectively encoding an acetoin dehydrogenase regulator and meso-2,3-BD dehydrogenase. To further confirm the physiological effects on acetoin and 2,3 BD biosynthesis, gene editing was performed using the CRISPR-Cas9 system, followed by phenotypic screening and genotype validation. The knockout of acoR and budC increased the acetoin maximum titer by 21.2 % and 49.2 %, respectively. Moreover, the optical purity of D-(-)-2,3-BD reached 92.7 % following the knockout of budC. Heterologous expression of acoR from B. licheniformis 2709 in both the wild type and acoR knockout mutant strongly inhibited acetoin accumulation compared to native acoR, which emphasized the regulatory role of AcoR in acetoin accumulation. Conversely, complementation of budC restored the synthesis of meso-2,3-BD synthesis, emphasizing its importance in this process. Overexpression of alsD in the acoR mutant increased the 2,3-BD titer by 61.9 % to 121.97 g/L, while the productivity reached 2.03 g/L·h. Finally, co-expression of bdhA and gldA increased 2,3-BD production by 25.6 %. This study elucidated the dual regulatory roles of acoR and budC in acetoin and 2,3-BD metabolism, establishing a "knockout-overexpression" synergic strategy, which offers theoretical support and practical guidance for further strain optimization.