Modulation of ADH activity in Zymomonas mobilis provides significant flux redirection away from ethanol

Zymomonas mobilis has an extremely high specific glucose uptake rate and produces ethanol at high yields and productivities. For synthesizing products beyond ethanol in Z. mobilis, reducing ethanol yields is a major challenge. Previous efforts have sought to decrease PDC activity to minimize ethanol formation. Here, we sought to modulate ADH (encoded by adhA and adhB genes) activity to redirect flux away from ethanol. We found that deletion of adhB combined with co-expression of a heterologous NAD(P) regenerating enzyme (L-LDH) diverted more than 50 % of carbon flux away from ethanol formation. The sequential deletion of adhA in the adhB-deleted strain led to ∼90 % reduction in ADH activity. During batch growth, the strain showed ∼90 % reduction in ethanol titres (27 mM) compared to WT (209 mM) and significant flux redirection toward L-LA formation (169 mM). The results demonstrate that modulation of ADH activity by deletion of adhA and adhB genes is an effective strategy for rediverting flux toward products beyond ethanol in Z. mobilis.