Fig. 2
Pathways used to produce muconic acid from glucose and xylose. Glucose and xylose are converted after uptake into phosphoenolpyruvate (PEP) and erythrose-4-phosphate (E4P) by the glycolytic and pentose-phosphate pathways. The two compounds are combined to enter the shikimate pathway and produce 3-dihydroshikimate (DHS), which is then converted using the bacterial heterologous pathway for muconic acid biosynthesis (MApw) into protocatechuic acid (PCA), catechol and muconic acid. The MApw consists of a DHS dehydratase from Podospora anserina (aroZPan), PCA decarboxylase (PCAD) from K. pneumoniae (aroY-Ciso) and catechol dioxygenase (CDO) from C. albicans (HQD2Ca). Feedback inhibition of aromatic amino acids acting on Aro3 and Aro4, has been relieved by deletion of Aro3 and site-specific mutagenesis of Aro4 (ARO4K229L). Overexpression of PAD1 stimulates production of prenylated flavine mononucleotide (prFMN), a co-factor of the protocatechuic acid decarboxylase (PCAD) enzyme encoded by aroY-Ciso. To further enhance muconic acid production, the synthesis of ethanol was abolished by deletion of the pyruvase decarboxylase (PDC) genes (pdcΔ). Muconic acid is exported from the cells by one or more unknown carriers