Production of 1,4-butanediol through <i>Clostridia</i> C4 pathways

1,4-butanediol (1,4-BDO) is an important building block in the chemical industry that has been mainly produced from fossil fuels, but now biosynthesis of 1,4-BDO has received more and more attention due to environmental issues. The Clostridia C4 pathway produces an intermediate crotonyl-CoA which could be diverted to 1,4-BDO by 4-hydroxybutyryl-CoA dehydratase (4HBD). Here, we compared this pathway with other 1,4-BDO biosynthesis pathways and illustrated its potential advantages regarding cellular energy conservation and theoretical yield. Then, the feasibility of 1,4-BDO production in this way was tested by introducing a single 4HBD in Clostridium acetobutylicum that natively produced the C4 intermediate and a variety of aldehyde/alcohol dehydrogenases (AdhE). Five different 4HBD genes were screened and the Cbei-2100 gene from Clostridium beijerinckii was the most effective, producing 0.066 mg/mL of 1,4-BDO. To block the metabolic flux towards the main product butanol, disruption of butyryl-CoA dehydrogenase (Bcd) was tried but failed, while inactivation of its homologue (FAD/FMN-containing dehydrogenase, Fcd) obtained little effect. Alternatively, the electron-transferring flavoprotein EtfA coupled with Bcd was inactivated, and 1,4-BDO production was greatly increased to 0.182 mg/mL. In conclusion, this study demonstrated the feasibility of 1,4-BDO production through the Clostridia C4 pathway. Further blocking of the competing flux towards butanol would be effective to improve the production of in the future.