Use of an Alternative Pathway for the Synthesis of Isoleucine in Escherichia coli Threonine-Producing Strains

An E. coli strain in which all known pathways of threonine catabolism were inactivated (Δtdh, ΔltaE, ΔAilvA, ΔtdcB, AyiaY) has been constructed. The possibility of an alternative pathway for the isoleucine synthesis by expressing heterologous citramalate synthase from Leptospira interrogans in an E. coli strain carrying the ΔilvA deletion was demonstrated. It was observed that the cimA overexpression has a negative effect on the threonine production. We developed a system for regulated gene expression based on the inducible promoter PLtetO and TetR repressor of the tetracycline operon. A threonine producing strain B-1201 in which the cimA gene is expressed under the control of the regulated promoter was constructed. A correlation of the threonine productivity and the expression level of the cimA gene was shown by culturing the B-1201 strain in fermenter. The optimal inductor content for the maximum threonine accumulation was also determined. Escherichia coli, strain, threonine, citramalate synthase This work was supported by the Ministry of Education and Science of the Russian Federation (project code RFMEFI61017X0011), and it was carried out using the equipment of the National Bio-Resource Center «All-Russian Collection of Industrial Microorganisms», NRC «Kurchatov Institute» - GOSNIIGENETIKA. The authors are grateful to Dr. I. V. Manukhov for providing the MG1655Z1strain and pZE21-lux plasmid, and for teaching techniques of bioluminescence measuring.