Osmoadaptation in rhizobia: ectoine-induced salt tolerance-猫眼课题宝

根瘤菌的渗透适应：四氢嘧啶诱导的耐盐性

DOI：

10.1128/jb.176.17.5210-5217.1994

发表时间：

1994

期刊：

Journal of Bacteriology

影响因子：

3.2

通讯作者：

中科院分区：

生物学3区

文献类型：

作者：

R. Talibart;Mohamed Jebbar;G. Gouesbet;S. Himdi;H. Wróblewski;Carlos Blanco;T. Bernard

在证明了异托碱（一种四氢嘧啶）对大肠杆菌具有渗透保护特性后（M. Jebbar， R. Talibart， K. Gloux， T. Bernard, and Blanco， J. Bacteriol. 174:5027-5035, 1992），我们研究了该分子在根瘤菌渗透适应中的作用。在不利渗透条件下（0.5 M NaCl），异托碱与甘氨酸甜菜碱的促生长效果几乎相同。此外，对甜菜碱不敏感的根瘤菌的生长也有所改善。外托碱的转运被证明是可诱导的，依赖于周围质蛋白，并且，如竞争实验所示，与甘氨酸甜菜碱的转运不同。当NaCl浓度从0提高到0.3或0.5 M时，介质渗透压对蛋白质-1的吸收特性影响不大，因为当运输常数为80微米时，蛋白质-1的内流速率从12增加到仅20 nmol min-1 mg。天然丰度的13c核磁共振和放射性标记试验表明，与甘氨酸甜菜碱不同，异托因不会在细胞内积累，因此不会抑制内源性相容溶质（谷氨酸、n -乙酰谷氨酰胺酰谷氨酰胺和海藻糖）的合成。此外，在存在外托因的渗透应激细胞中，谷氨酸含量的强烈上升表明，外托因不参与渗透平衡的恢复，而是在触发内源性渗透产物的合成中发挥关键作用。因此，我们认为至少有两种不同的渗透保护剂：如甘氨酸甜菜碱或谷氨酸，它们是真正的渗透剂，而如异托因，它们是化学介质。

After having shown that ectoine (a tetrahydropyrimidine) displays osmoprotective properties towards Escherichia coli (M. Jebbar, R. Talibart, K. Gloux, T. Bernard, and Blanco, J. Bacteriol. 174:5027-5035, 1992), we have investigated the involvement of this molecule in the osmotic adaptation of Rhizobium meliloti. Ectoine appeared almost as effective as glycine betaine in improving the growth of R. meliloti under adverse osmotic conditions (0.5 M NaCl). Moreover, improvement of growth of rhizobial strains insensitive to glycine betaine was also observed. Ectoine transport proved inducible, periplasmic protein dependent, and, as shown by competition experiments, distinct from the transport of glycine betaine. Medium osmolarity had little effect on the uptake characteristics, since the rate of influx increased from 12 to only 20 nmol min-1 mg of protein-1 when NaCl concentrations were raised from 0 to 0.3 or 0.5 M, with a constant of transport of 80 microM. Natural-abundance 13C-nuclear magnetic resonance and radiolabelling assays showed that ectoine, unlike glycine betaine, is not intracellularly accumulated and, as a consequence, does not repress the synthesis of endogenous compatible solutes (glutamate, N-acetylglutaminylglutamine amide, and trehalose). Furthermore, the strong rise in glutamate content in cells osmotically stressed in the presence of ectoine suggests that, instead of being involved in osmotic balance restoration, ectoine should play a key role in triggering the synthesis of endogenous osmolytes. Hence, we believe that there are at least two distinct classes of osmoprotectants: those such as glycine betaine or glutamate, which act as genuine osmolytes, and those such as ectoine, which act as chemical mediators.

In vitro reconstitution of osmoregulated expression of proU of Escherichia coli.