Metabolic engineering of Klebsiella pneumoniae for the production of cis,cis-muconic acid.

cis,cis-Muconic acid (ccMA), a metabolic intermediate of Klebsiella pneumoniae, can be converted to adipic acid and terephthalic acid, which are important monomers of synthetic polymers. However, wild-type K. pneumoniae does not produce ccMA because intracellular carbon flow does not favor ccMA biosynthesis. In this study, several metabolic engineering strategies were used in an attempt to modify the wild-type strain to induce it to produce ccMA. First, by blocking the synthesis of aromatic amino acids, 343 mg/L of catechol, a precursor of ccMA, was produced. Then, the native catechol 1,2-dioxygenasegene (catA) was overexpressed, which caused the strain to convert the catechol to ccMA. The production of ccMA was further improved by deletion of the muconate cycloisomerase gene (catB) and by deleting a feedback inhibitor of the aromatic amino acid pathway. Further improvement was achieved by adjusting the pH of the culture broth. The developed strain produced 2.1 g/L of ccMA in flask cultivation. The results showed the potential of K. pneumoniae as a ccMA producer.