Co-production of acetoin and succinic acid by metabolically engineered Enterobacter cloacae

Background Renewable chemicals have attracted attention due to increasing interest in environmental concerns and resource utilization. Biobased production of industrial compounds from nonfood biomass has become increasingly important as a sustainable replacement for traditional petroleum-based production processes depending on fossil resources. Therefore, we engineered an Enterobacter cloacae budC and ldhA double-deletion strain (namely, EC increment budC increment ldhA) to redirect carbon fluxes and optimized the culture conditions to co-produce succinic acid and acetoin. Results In this work, E. cloacae was metabolically engineered to enhance its combined succinic acid and acetoin production during fermentation. Strain EC increment budC increment ldhA was constructed by deleting 2,3-butanediol dehydrogenase (budC), which is involved in 2,3-butanediol production, and lactate dehydrogenase (ldhA), which is involved in lactic acid production, from the E. cloacae genome. After redirecting and fine-tuning the E. cloacae metabolic flux, succinic acid and acetoin production was enhanced, and the combined production titers of acetoin and succinic acid from glucose were 17.75 and 2.75 g L-1, respectively. Moreover, to further improve acetoin and succinic acid production, glucose and NaHCO3 modes and times of feeding were optimized during fermentation of the EC increment budC increment ldhA strain. The maximum titers of acetoin and succinic acid were 39.5 and 20.3 g L-1 at 72 h, respectively. Conclusions The engineered strain EC increment budC increment ldhA is useful for the co-production of acetoin and succinic acid and for reducing microbial fermentation costs by combining processes into a single step.

Automated summary

This study engineered E. cloacae to enhance the co-production of succinic acid and acetoin through metabolic flux redirection. By optimizing the culture conditions, the production of acetoin and succinic acid was further increased.