Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aobayama 6-6-07, Sendai, 980-8579, Japan.
Sci Rep. 2017 May 18;7(1):2122. doi: 10.1038/s41598-017-02164-7.
The physiological effects of caesium (Cs) on living cells are poorly understood. Here, we examined the physiological role of Cs on the activity of the potassium transporters in E. coli. In the absence of potassium (K), Kup-mediated Cs uptake partially supported cell growth, however, at a much lower rate than with sufficient K. In K-limited medium (0.1 mM), the presence of Cs (up to 25 mM) in the medium enhanced growth as much as control medium containing 1 mM K. This effect depended on the maintenance of basal levels of intracellular K by other K uptake transporters. Higher amounts of K (1 mM) in the medium eliminated the positive effect of Cs on growth, and revealed the inhibitory effect of high Cs on the growth of wild-type E. coli. Cells lacking Kdp, TrkG and TrkH but expressing Kup grew less well when Cs was increased in the medium. A kdp mutant contained an increased ratio of Cs/K in the presence of high Cs in the medium and consequently was strongly inhibited in growth. Taken together, under excess Cs conditions Kup-mediated Cs influx sustains cell growth, which is supported by intracellular K supplied by Kdp.
铯（Cs）对活细胞的生理影响知之甚少。在这里，我们研究了 Cs 对大肠杆菌中钾转运蛋白活性的生理作用。在没有钾（K）的情况下，Kup 介导的 Cs 摄取部分支持细胞生长，但速度比有足够 K 时慢得多。在 K 限制培养基（0.1 mM）中，培养基中 Cs（高达 25 mM）的存在与含有 1 mM K 的对照培养基一样促进生长。这种效应取决于其他 K 摄取转运蛋白维持细胞内 K 的基础水平。培养基中更高浓度的 K（1 mM）消除了 Cs 对生长的积极影响，并揭示了高 Cs 对野生型大肠杆菌生长的抑制作用。当培养基中 Cs 增加时，缺乏 Kdp、TrkG 和 TrkH 但表达 Kup 的细胞生长情况较差。在培养基中存在高 Cs 的情况下，kdp 突变体中 Cs/K 的比例增加，因此其生长受到强烈抑制。综上所述，在过量 Cs 条件下，Kup 介导的 Cs 内流维持细胞生长，这由 Kdp 提供的细胞内 K 支持。
