초록
<P>L-threonine is an essential amino acid used widely in food, cosmetics, animal feed and medicine. The <I>thrABC</I> operon plays an important role in regulating the biosynthesis of L-theronine. In this work, we systematically analyzed the effects of separating <I>thrAB</I> and <I>thrC</I> in different proportions on strain growth and L-threonine production in <I>Escherichia coli</I> firstly. The results showed that higher expression of <I>thrC</I> than <I>thrAB</I> enhanced cell growth and L-threonine production; however, L-threonine production decreased when the <I>thrC</I> proportion was too high. The highest L-threonine production was achieved when the expression intensity ratio of <I>thrAB</I> to <I>thrC</I> was 3:5. Secondly, a stationary phase promoter was also used to dynamically regulate the expression of engineered <I>thrABC</I>. This strategy improved cell growth and shortened the fermentation period from 36 h to 24 h. Finally, the acetate metabolic overflow was reduced by deleting the <I>ptsG</I> gene, leading to a further increase in L-threonine production. With these efforts, the final strain P<I>2.1</I>-2901Δ<I>ptsG</I> reached 40.06 g/L at 60 h fermentation, which was 96.85% higher than the initial control strain TH and the highest reported titer in shake flasks. The maximum L-threonine yield and productivity was obtained in reported fed-batch fermentation, and L-threonine production is close to the highest titer (127.30 g/L). In this work, the expression ratio of genes in the <I>thrABC</I> operon in <I>E. coli</I> was studied systematically, which provided a new approach to improve L-threonine production and its downstream products.</P>