Fig. 1

Metabolic map of the two investigated iBuOH producer strains RL3000Δferm-pIBA4 (top) and SB001-pIBA4 (bottom) for anaerobic conditions. The (green) gene names indicate the heterologous genes that were introduced via plasmid pIBA4 [alsS_Bsu encodes the acetolactate synthase (ALS), ilvC _Eco* encodes the ketol-acid reductoisomerase (KARI), ilvD _Eco encodes the dihydroxy-acid dehydratase (DHAD), kivd_Lla encodes the 2-ketoacid decarboxylase (KDC), and adhA _Lla* encodes the alcohol dehydrogenase (ADH)]. Red crosses and the corresponding red gene names indicate the deleted pathways. Green arrows indicate the redox-balanced pathway from glucose to iBuOH. Blue arrows indicate the pathway from acetate to ethanol, oxidizing 2 molecules of NADH and consuming 1 molecule of ATP per molecule of acetate. The purple cross indicates the redox-imbalance and thus infeasibility of cell growth in strain RL3000Δferm-pIBA4. 2-AL 2-acetolactate, AKG α-ketoglutarate, DHIV 2,3-dihydroxyisovalerate, G6P glucose 6-phosphate, IBAL isobutyraldehyde, iBuOH isobutanol, KIV 2-ketoisovalerate, MQH₂ menaquinol, PEP phosphoenolpyruvate