Department of Biology, Faculty of Art and Sciences, Dumlupinar University, Kütahya, Turkey.
Pol J Microbiol. 2009;58(4):307-17.
When exposed extreme environmental conditions such as sea water, bacteria have been shown different survival strategy for continue their life. One of this strategy known as viable but nonculturable (VBNC) state which is very important for nondifferiation bacteria. VBNC cells cause serious human health problems. Little is known, however, about the genetic mechanisms underlying the VBNC state. Under different environmental conditions, porins are important in the survival strategy of bacteria. EnvZ/OmpR work together as regulators of ompF and ompC gene expression. It is known that the EnvZ system has a role in VBNC state. In this study we tried to find out the viability of EnvZ, OmpC and OmpF mutant E. coli under stress effect of osmolarity, pH and starvation. Bacteria were suspended in filtered-autoclaved sea water microcosms and numbers determined over 25 day incubation periods by plate count (PC), direct viable count (DVC) and count of cells capable of respiration (RCC). As regard to results, alkaline pH affected E. coli more than acidic pH, which led to decline in number. On the contrary glycine betaine addition to sea water protected E. coli porin mutants and also reduced the death rate of bacteria. Under the effect of pH, osmotic stress and starvation stress, wild type E. coli and porin mutants entered a dormant state or became VBNC with the exception of MSZ31 (envZ mutant) E. coli cells which did not enter the VBNC state under the three tested stress conditions. This study is the first report to demonstrate that E. coli could not enter the VBNC state in the lack of EnvZ product under the stress of osmolarity, pH and starvation and the relationship between EnvZ and VBNC state are not affected by pH, osmolarity and starvation.
当暴露于极端环境条件下，如海水时，细菌已经表现出不同的生存策略以继续其生命。其中一种策略称为活但不可培养（VBNC）状态，这对于非分化细菌非常重要。VBNC 细胞会导致严重的人类健康问题。然而，对于 VBNC 状态的遗传机制知之甚少。在不同的环境条件下，孔蛋白在细菌的生存策略中很重要。EnvZ/OmpR 共同作为 ompF 和 ompC 基因表达的调节剂。已知 EnvZ 系统在 VBNC 状态中起作用。在这项研究中，我们试图在渗透压、pH 值和饥饿的应激作用下，找出 VBNC 状态下的 EnvZ、OmpC 和 OmpF 突变大肠杆菌的生存能力。将细菌悬浮在过滤消毒的海水微宇宙中，并通过平板计数（PC）、直接活菌计数（DVC）和能够呼吸的细胞计数（RCC）在 25 天的孵育期内确定数量。结果表明，碱性 pH 值比酸性 pH 值对大肠杆菌的影响更大，导致数量下降。相反，甘氨酸甜菜碱添加到海水中保护大肠杆菌孔蛋白突变体，也降低了细菌的死亡率。在 pH 值、渗透压和饥饿应激的影响下，野生型大肠杆菌和孔蛋白突变体进入休眠状态或成为 VBNC，除了 MSZ31（envZ 突变体）大肠杆菌细胞在三种测试的应激条件下未进入 VBNC 状态。这项研究首次表明，在渗透压、pH 值和饥饿应激下缺乏 EnvZ 产物时，大肠杆菌不能进入 VBNC 状态，并且 EnvZ 与 VBNC 状态之间的关系不受 pH 值、渗透压和饥饿的影响。
