Pathway engineering for the production of aromatic compounds in Escherichia coli

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Abstract
Glucose is the preferred substrate for certain fermentation processes. During its internalization and concomitant formation of glucose-6-phosphate through the glucose phosphotransferase system (PTS), one molecule of phosphoenolpyruvate (PEP) is consumed. Together with erythrose 4-phosphate (E4P), PEP is condensed to form 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP), the first intermediate of the common segment of the aromatic pathway. From this metabolic route, several commercially important aromatic compounds can be obtained. We have selected Escherichia coli mutants that can transport glucose efficiently by a non-PTS uptake system. In theory, this process should increase the availability of PEP for other biosynthetic reactions. Using these mutants, in a background where the DAHP synthase (the enzyme that catalyzes the condensation of PEP and E4P into DAHP) was amplified, we were able to show that at least some of the PEP saved during glucose transport, can be redirected into the aromatic pathway. This increased carbon commitment to the aromatic pathway was enhanced still further upon amplification of the E. coli tktA gene that encodes for a transketolase involved in the biosynthesis of E4P.