A Study of the Influence of L-Lysine and its Transporter LysP on the Characteristics of the L-Threonine Producer Strain

In this work, it was shown for the first time that inactivation of the L-lysine uptake transport system from the external environment leads to an increase in the level of L-threonine synthesis by the Escherichia coli strain that produces it, while the addition of lysine to the culture medium reduces the productivity of the unmodified strain, which indicates the influence of the intracellular pool of lysine on the efficiency of threonine biosynthesis. A study of the possible mechanisms of this influence showed that neither the previously known inhibition of aspartate kinase III (LysC) activity, nor the repression of the synthesis of aspartate semialdehyde dehydrogenase (Asd) and glutamate dehydrogenase (GdhA) individually are reasons for the decrease in culture productivity. The results we obtained may indicate both the presence of a previously unknown mechanism for the regulation of threonine metabolism by lysine and the fact that several enzymes in the threonine biosynthesis pathway are simultaneously affected by this amino acid. At the same time, changing the permeability of the membrane to lysine, or reducing its intracellular concentration as a result of changing the efficiency of its biosynthesis, is a promising approach for improving threonine-producing strains.