Fig. 6

Metabolic pathways for the production of 2,3-butanediol (2,3-BDO). Different stereoisomers of 2,3-BDO can be produced from glucose by four metabolic pathways via acetolactate. Meso-2,3-BDO can be synthesized from acetolactate by acetolactate decarboxylase and S-specific 2,3-BDO dehydrogenase (route ①, illustrated by green colors) or from diacetyl by diacetyl reductase and S-specific 2,3-BDO dehydrogenase (route ②, illustrated by yellow colors). (2R,3R)-BDO can be synthesized from acetolactate by acetolactate decarboxylase and R-specific 2,3-BDO dehydrogenase (route ③, illustrated by orange colors). (2S,3S)-BDO can be synthesized from diacetyl by diacetyl reductase and S-specific 2,3-BDO dehydrogenase (route ④, illustrated by blue colors). ackA acetate kinase, adhE acetaldehyde/alcohol dehydrogenase, budA acetolactate decarboxylase, budB acetolactate synthase, budC S-specific 2,3-BDO dehydrogenase, dhaD glycerol dehydrogenase, ldhA lactate dehydrogenase, pfl pyruvate formate lyase, pta phosphate acetyltransferase