Genetic modifications to push L-tyrosine synthesis in Escherichia coli

Abstract

L-tyrosine, an aromatic amino acid, has attracted increasing attention owing to its wide application in industrial settings. Nonetheless, to obtain strains with high efficiency in producing L-tyrosine still faces challenges. In this study, a recombinant bacteria with the ability to accumulate L-tyrosine efficiently was identified after analysis of constructed strains obtained by different genetic modifications. For the first strain (TYR02), aroG fbr was up-regulated and tyrR was knocked out to relieve the repression of multiple genes in the L-tyrosine synthesis pathway by TyrR (encoded by tyrR). For the second set of strains (TYR03 and TYR04), the transcription of tyrA fbr B was enhanced by the trc and T7 promoters based on TY02 respectively. In the third set of strains (TYR05 and TYR06), the transcription of tyrA fbr B was enhanced by the trc and T7 promoters respectively, and aroG fbr was up-regulated. TYR02 exhibited relatively efficient on L-tyrosine accumulation in shake flask cultures after 24 h. Notably, up-regulation of the transcript level of tyrA fbr B did not show the predicted effects, while the manifested traits of knocking out tyrR disappeared after up-regulated expression of tyrA fbr B. After 25 h of fed-batch fermentation in a 30 L fermentor, TYR02 accumulated L-tyrosine about 50.2 g/L, representing the highest concentration in such a short fermentation time.