n-Butanol and ethanol production from cellulose by Clostridium cellulovorans overexpressing heterologous aldehyde/alcohol dehydrogenases.

• Different aldehyde/alcohol dehydrogenases were expressed in C. cellulovorans. • Strain overexpressing adh E2 produced 4 g/L n -butanol with a high yield of 0.22 g/g. • Co-expressing bdh B with adh E2 decreased overall butanol production. • Co-expressing adh E1 and bdh B had the highest selectivity for butanol over ethanol. With high cellulolytic and acetic/butyric acids production abilities, Clostridium cellulovorans is promising for use to produce cellulosic n -butanol. Here, we introduced three different aldehyde/alcohol dehydrogenases encoded by bdh B, adh E1, and adh E2 from Clostridium acetobutylicum into C. cellulovorans and studied their effects on ethanol and n -butanol production. Compared to AdhE2, AdhE1 was more specific for n -butanol biosynthesis over ethanol. Co-expressing adh E1 with bdh B produced a comparable amount of butanol but significantly less ethanol, leading to a high butanol/ethanol ratio of 7.0 and 5.6 (g/g) in glucose and cellulose fermentation, respectively. Co-expressing adh E1 or adh E2 with bdh B did not increase butanol production because the activity of BdhB was limited by the NADPH availability in C. cellulovorans. Overall, the strain overexpressing adh E2 alone produced the most n -butanol (4.0 g/L, yield: 0.22 ± 0.01 g/g). Based on the insights from this study, further metabolic engineering of C. cellulovorans for cellulosic n -butanol production is suggested. [ABSTRACT FROM AUTHOR]