Abstract:Phosphoenolpyruvate, the precursor of L-threonine synthesis, is consumed by the nitrogen phosphotransferase system (PTSNtr) of Escherichia coli, so the deletion of genes related to PTSNtr may affect the synthesis of L-threonine. In this study, ptsP, ptsO and ptsN genes encoding the component proteins of PTSNtr in E.coli MG1655 were deleted using CRISPR-Cas9 system, and the corresponding mutants MZ001, MZ002 and MZ003 were constructed. The results showed that the single deletion of ptsP、ptsO or ptsN led to slower growth in the early stage and longer lag period. The mutant strains grew fast in the later stable stage and their biomass accumulation was greater than that of the original strain. Then, the expression plasmid pFW01-thrA*BC-rhtC, which contained thrA*、thrB and thrC encoding threonine synthesis as well as rhtC encoding threonine transporter, was introduced into the original and mutant strains. In comparison with MG1655/pFW01-thrA*BC-rhtC, the L-threonine titer of MZ001/pFW01-thrA*BC-rhtC, MZ002/pFW01-thrA*BC-rhtC and MZ003/pFW01-thrA*BC-rhtC significantly increased by 3.805 g/L, 1.722 g/L and 3.091 g/L, respectively. The results showed that the deletion of genes related to PTSNtr of E. coli promoted the synthesis of L-threonine
