Fig. 1

Schematic diagram of the assembled modules to convert galactose to n-butanol. In galactose utilization module, β-d-galactose is converted into α-d-glucose-6-phosphate through the Leloir pathway, which is a more complicated enzymatic pathway than that required for glucose. Acetoacetyl-CoA from α-d-glucose-6-phosphate is transformed into n-butanol by the n-butanol production module. Four moles of NADH generated from one mole of galactose are used in the n-butanol biosynthesis. In NADH supplementation module, additional NADH is produced by converting formate to carbon dioxide. The red arrows indicate the homologous and heterologous overexpression of genes. The blue arrow represents controllable expression of fdh1 for optimal n-butanol production