Effects of TdcC、SstT and LIV-1 systems deletion of Escherichia coli on extracellular L-threonine accumulation

Abstract:

[Objective] The effects of the threonine absorption system deletion, containing TdcC, SstT and LIV-1, on the extracellular accumulation of threonine were investigated in Escherichia coli. [Methods] In this paper, the TdcC, SstT and LIV-1 systems single- and muti-deletion of E. coli W3110 were constructed by deleting the corresponding genes (tdcC, sstT, livJ). Subsequently, the plasmid harboring the operon gene cluster of threonine, pKKthrAC1034TBC, was transformed into both the wild type and recombinant strains. The ability of absorption and extracellular accumulation of threonine was then detected. [Results] Compared with W3110, the threonine absorption ability of T04 with tdcC and sstT deletion was decreased by 43.28%. Meanwhile, T04 with plasmid pKKthrAC1034TBC accumulated 1.09 g/L threonine in vitro, which was 2.7 folds of that of strain W3110 with pKKthrAC1034TBC. Further deletion of livJ gene in T04 generated T07, which resulted in 12.97% decrease of threonine absorption. However, the maximum extracellular threonine concentration of strain T07 with pKKthrAC1034TBC was only 0.63 g/L, which was decreased by 42.2% when compared with that of strain T04 with pKKthrAC1034TBC. [Conclusion] Deletion of both TdcC and SstT systems of E. coli significantly decreased threonine absorption and improved extracellular threonine accumulation. Though inactivation of LIV-1 system reduced threonine absorption, it would impair the accumulation of threonine in vitro.

Key words:L-threonine, Escherichia coli, Absorption system, Gene knockout