Renewable synthesis of n-butyraldehyde from glucose by engineered Escherichia coli

BACKGROUND: n-Butyraldehyde is a high-production volume chemical produced exclusively from hydroformylation of propylene. It is a versatile chemical used in the synthesis of diverse C4–C8 alcohols, carboxylic acids, esters, and amines. Its high demand and broad applications make it an ideal chemical to be produced from biomass. RESULTS: An Escherichia coli strain was engineered to produce n-butyraldehyde directly from glucose by expressing a modified Clostridium CoA-dependent n-butanol production pathway with mono-functional Coenzyme A-acylating aldehyde dehydrogenase (Aldh) instead of the natural bifunctional aldehyde/alcohol dehydrogenase. Aldh from Clostridium beijerinckii outperformed the other tested homologues. However, the presence of native alcohol dehydrogenase led to spontaneous conversion of n-butyraldehyde to n-butanol. This problem was addressed by knocking out native E. coli alcohol dehydrogenases, significantly improving the butyraldehyde-to-butanol ratio. This ratio was further increased reducing media complexity from Terrific broth to M9 media containing 2% yeast extract. To increase production titer, in situ liquid–liquid extraction using dodecane and oleyl alcohol was investigated. Results showed oleyl alcohol as a better extractant, increasing the titer of n-butyraldehyde produced to 630 mg/L. CONCLUSION: This study demonstrated n-butyraldehyde production from glucose. Through sequential strain and condition optimizations, butyraldehyde-to-butanol ratio was improved significantly compared to the parent strain. Results from this work may serve as a basis for further development of renewable n-butyraldehyde production. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13068-017-0978-7) contains supplementary material, which is available to authorized users.