Modulating the direction of carbon flow in Escherichia coli to improve l-tryptophan production by inactivating the global regulator FruR

• FruR was inactivated in l-tryptophan production strain Escherichia coli FB-04, forming FB-04(ΔfruR).
• FB-04(ΔfruR) maintained higher vitality and growth efficiency.
• FB-04(ΔfruR) showed substantially improved l-tryptophan production.
• Knockout of fruR improved the efficiency of the carbon source utilization.
• Knockout of fruR improved the levels of critical precursors and substrates for l-tryptophan biosynthesis by modulating the direction of carbon flow.

The fructose repressor (FruR) affects carbon flux through the central metabolic pathways of Escherichia coli. In this study, l-tryptophan production in Escherichia coli FB-04 was improved by knocking out the fruR gene, thereby inactivating FruR. This fruR knockout strain, E. coli FB-04(ΔfruR), not only exhibited higher growth efficiency, it also showed substantially improved l-tryptophan production. l-tryptophan production by E. coli FB-04(ΔfruR) and l-tryptophan yield per glucose were increased by 62.5% and 52.4%, respectively, compared with the parent E. coli FB-04. Metabolomics analysis showed that the fruR knockout significantly enhances metabolic flow through glycolysis, the pentose phosphate pathway and the TCA cycle, increasing levels of critical precursors and substrates for l-tryptophan biosynthesis. These results indicate that fruR deletion should enhance l-tryptophan production and improve the efficiency of carbon source utilization independent of genetic background.