Holland I B, Jones H E, Campbell A K, Jacq A
Institut de Génétique et Microbiologie, UMR CNRS 8621, Université Paris-Sud, Bâtiment 409,0, 91405 Orsay Cedex, France.
Biochimie. 1999 Aug-Sep;81(8-9):901-7. doi: 10.1016/s0300-9084(99)00205-9.
We have previously proposed that fluctuations in Ca(2+) levels should play an important role in bacteria as in eukaryotes in regulating cell cycle events (Norris et al., J. Theor. Biol. 134 (1998) 341-350). This proposal implied the presence of Ca(2+) uptake systems in bacteria, cell cycle mutants simultaneously defective in Ca(2+)-homeostasis, and perturbation of cell cycle processes when cellular Ca(2+) levels are depleted. We review the properties of new cell cycle mutants in E. coli and B. subtilis resistant to inhibitors of calmodulin, PKC or Ca(2+)-channels; the evidence for Ca(2+)-binding proteins including Acp and FtsZ; and Ca(2+)-transporters. In addition, the effects of EGTA and verapamil (a Ca(2+) channel inhibitor) on growth, protein synthesis and cell cycle events in E. coli are described. We also describe new measurements of free Ca(2+)-levels, using aequorin, in E. coli. Several new cell cycle mutants were obtained using this approach, affecting either initiation of DNA replication or in particular cell division at non-permissive temperature. Several of the mutants were also hypersensitive to EGTA and or Ca(2+). However, none of the mutants apparently involved direct alteration of a drug target and surprisingly in some cases involved specific tRNAs or a tRNA synthetase. The results also indicate that the expression of several genes in E. coli may be regulated by Ca(2+). Cell division in particular appears very sensitive to the level of cell Ca(2+), with the frequency of division clearly reduced by EGTA and by verapamil. However, whilst the effect of EGTA was clearly correlated with depletion of cellular Ca(2+) including free Ca(2+), this was not the case with verapamil which appears to change membrane fluidity and the consequent activity of membrane proteins. Measurement of free Ca(2+) in living cells indicated levels of 200-300 nM, tightly regulated in wild type cells in exponential phase, somewhat less so in stationary phase, with apparently La(2+)-sensitive PHB-polyphosphate complexes involved in Ca(2+) influx. The evidence reviewed increasingly supports a role for Ca(2+) in cellular processes in bacteria, however, any direct link to the control of cell cycle events remains to be established.
我们之前曾提出，正如在真核生物中一样，Ca(2+)水平的波动在细菌调节细胞周期事件中应发挥重要作用（Norris等人，《理论生物学杂志》134 (1998) 341 - 350）。这一观点意味着细菌中存在Ca(2+)摄取系统、Ca(2+)稳态同时存在缺陷的细胞周期突变体，以及细胞内Ca(2+)水平耗尽时细胞周期进程的扰动。我们综述了大肠杆菌和枯草芽孢杆菌中对钙调蛋白、蛋白激酶C或Ca(2+)通道抑制剂有抗性的新细胞周期突变体的特性；包括Acp和FtsZ在内的Ca(2+)结合蛋白的证据；以及Ca(2+)转运蛋白。此外，还描述了EGTA和维拉帕米（一种Ca(2+)通道抑制剂）对大肠杆菌生长、蛋白质合成和细胞周期事件的影响。我们还描述了使用水母发光蛋白对大肠杆菌中游离Ca(2+)水平进行的新测量。使用这种方法获得了几个新的细胞周期突变体，它们在非允许温度下影响DNA复制的起始或特别是细胞分裂。其中一些突变体对EGTA和/或Ca(2+)也高度敏感。然而，这些突变体似乎都没有直接改变药物靶点，令人惊讶的是，在某些情况下涉及特定的tRNA或一种tRNA合成酶。结果还表明，大肠杆菌中几个基因的表达可能受Ca(2+)调控。特别是细胞分裂似乎对细胞内Ca(2+)水平非常敏感，EGTA和维拉帕米明显降低了分裂频率。然而，虽然EGTA的作用与包括游离Ca(2+)在内的细胞内Ca(2+)耗尽明显相关，但维拉帕米并非如此，它似乎改变了膜流动性以及膜蛋白的后续活性。对活细胞中游离Ca(2+)的测量表明其水平为200 - 300 nM，在指数生长期的野生型细胞中受到严格调控，在稳定期则稍弱，显然La(2+)敏感的聚-β-羟基丁酸-多磷酸盐复合物参与了Ca(2+)内流。综述的证据越来越支持Ca(2+)在细菌细胞过程中的作用，然而，与细胞周期事件控制的任何直接联系仍有待确定。
