"Parallel Metabolic Pathway Engineering" for the Bioproduction of Shikimate Pathway Derivatives

Glucose and xylose are the major components of lignocellulosic biomass, and the effective use of both sugars contributes to improving the efficiency of bioproduction. Here we propose a method termed “parallel metabolic pathway engineering” (PMPE) for producing shikimate pathway derivatives from glucose–xylose co-substrate. In this method, we seek to use glucose mainly for target chemical production and xylose for supplying essential metabolites for cell growth. Glycolysis and the pentose phosphate pathway (PPP) are completely separated from the tricarboxylic acid (TCA) cycle. To recover cell growth, a xylose catabolic pathway that directly flows into the TCA cycle is introduced. We focused on the Dahms pathway which is a xylose catabolic pathway in Caulobacter crescentus, an oligotrophic bacterium. The Dahms pathway directly produces pyruvate and glyoxylate from xylose without glycolysis and PPP. To prove our concept, we produced cis,cis-muconic acid (MA) using the PMPE Escherichia coli strain. MA, a shikimate pathway derivative, is a valuable compound that is a precursor of important chemical compounds such as adipic acid and terephthalic acid, and its production has recently attracted attention. We modified the metabolic pathway of E. coli so that only glucose could be used for MA production, and we introduced the Dahms pathway to restore cell growth. As a result, we produce 4.09 g/L of MA using the PMPE E. coli strain with a high yield (0.31 g/g of glucose). The “PMPE” strategy will contribute to the development of clean processes for producing various valuable chemicals from lignocellulosic resources.