大肠杆菌TdcC、SstT和LIV-1系统缺失对胞外L-苏氨酸积累的影响

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

摘要:

【目的】比较分析苏氨酸吸收系统TdcC、SstT和LIV-1缺失对大肠杆菌吸收和积累胞外苏氨酸的影响。【方法】从菌株E. coli W3110出发，敲除tdcC、sstT和livJ基因，构建TdcC、SstT和LIV-1系统单缺失和多缺失菌株，将过量表达苏氨酸操纵子基因的重组质粒pKKthrAC1034TBC分别转入原始菌和重组菌，考察各菌株吸收和积累胞外苏氨酸的能力。【结果】敲除tdcC和sstT基因的重组菌T04的苏氨酸吸收能力比原始菌W3110降低了43.28%，T04 (pKKthrAC1034TBC)胞外苏氨酸积累量最高达到1.09 g/L，比对照菌W3110(pKKthrAC1034TBC)高出172.5%。敲除tdcC、sstT和livJ基因的重组菌T07的苏氨酸吸收能力比T04降低了12.97%，然而T07(pKKthrAC1034TBC)胞外苏氨酸积累量最大为0.63 g/L，与T04(pKKthrAC1034TBC)相比降低了42.2%。【结论】阻断TdcC和SstT系统，能有效降低大肠杆菌吸收苏氨酸的能力，提高苏氨酸的胞外积累量。阻断LIV-1系统，虽然能减少大肠杆菌对苏氨酸的吸收，却不利于菌株积累胞外苏氨酸。

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.