Fig. 6

Impact of heterologous 2,3-BDO metabolic pathway engineering and oxygen levels on native central carbon metabolism in Z. mobilis. This figure shows native central carbon metabolism in Z. mobilis which includes ED (Entner–Doudoroff), PPP (pentose phosphate pathway), and fermentation pathways leading to the production of ethanol and other minor metabolites of glycerol, lactate, and acetate from carbon source of glucose and xylose. The heterologous 2,3-BDO biosynthesis pathway was integrated into Z. mobilis metabolic pathway, which contains three enzymes of acetolactate synthase (Als), acetolactate decarboxylase (AldC), and butanediol dehydrogenase (Bdh) for 2,3-BDO biosynthesis from pyruvate. Depending on the source of Bdh enzyme from different microorganisms, three 2,3-BOD stereoisomers of R,R-2,3-BDO, S,S-2,3-BDO, and meso-2,3-BDO could be produced. Reactions involved in redox cofactor (NADH/NAD+) regeneration were shown as well as the respiration chain enzymes and electron transfer in Z. mobilis. The interactions among these pathways can help understand the impact of host carbon and energetic metabolism as well as oxygen levels on heterologous 2,3-BDO metabolic pathway engineering in Z. mobilis