A DIRECT COMPARISON OF APPROACHES FOR INCREASING CARBON FLOW TO AROMATIC BIOSYNTHESIS IN ESCHERICHIA-COLI

Different approaches to increasing carbon commitment to aromatic amino acid biosynthesis were compared in isogenic strains of Escherichia co li. In a strain having a wild-type PEP:glucose phosphotransferase (PTS ) system, inactivation of the genes encoding pyruvate kinase (pykA and pykF) resulted in a 3.4-fold increase in carbon flow to aromatic bios ynthesis. In a strain already having increased carbon flow to aromatic s by virtue of overexpression of the tktA gene (encoding transketolase ), the pykA and/or pykF mutations had no effect. A PTS- glucose(+) mut ant showed a 1.6-fold increase in carbon flow to aromatics compared to the PTS+ control strain. In the PTS- glucose(+) host background, over expression of tktA caused a further 3.7-fold increase in carbon flow, while inactivation of pykA and pykF caused a 5.8-fold increase. When a ll of the variables tested (PTS- glucose(+), pykA, pykF, and overexpre ssed tktA) were combined in a single strain, a 19.9-fold increase in c arbon commitment to aromatic biosynthesis was achieved.