2.3.1.190 synthesis engineering a budC acoABCD double mutant, which has lost 2,3-butanediol dehydrogenase activity and the acetoin dehydrogenase system for R-acetoin production. Optimized conditions include aerobic batch culture and mildly acidic conditions. 62.3 g per l R-acetoin can be produced by budC and acoABCD double mutants in 57 h culture, with an optical purity of 98.0%, and a substrate conversion ratio of 28.7% -, 736592