Genetic modifications to push <i>L</i> -tyrosine synthesis in <i>Escherichia coli</i>

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), aroGfbr 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 tyrAfbrB was enhanced by the trc and T7 promoters based on TY02 respectively. In the third set of strains (TYR05 and TYR06), the transcription of tyrAfbrB was enhanced by the trc and T7 promoters respectively, and aroGfbr 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 tyrAfbrB did not show the predicted effects, while the manifested traits of knocking out tyrR disappeared after up-regulated expression of tyrAfbrB. 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.