School of Biosciences, University of Birmingham, Birmingham, UK.
FEMS Microbiol Rev. 2014 Nov;38(6):1091-125. doi: 10.1111/1574-6976.12076. Epub 2014 Jul 2.
As part of their life cycle, neutralophilic bacteria are often exposed to varying environmental stresses, among which fluctuations in pH are the most frequent. In particular, acid environments can be encountered in many situations from fermented food to the gastric compartment of the animal host. Herein, we review the current knowledge of the molecular mechanisms adopted by a range of Gram-positive and Gram-negative bacteria, mostly those affecting human health, for coping with acid stress. Because organic and inorganic acids have deleterious effects on the activity of the biological macromolecules to the point of significantly reducing growth and even threatening their viability, it is not unexpected that neutralophilic bacteria have evolved a number of different protective mechanisms, which provide them with an advantage in otherwise life-threatening conditions. The overall logic of these is to protect the cell from the deleterious effects of a harmful level of protons. Among the most favoured mechanisms are the pumping out of protons, production of ammonia and proton-consuming decarboxylation reactions, as well as modifications of the lipid content in the membrane. Several examples are provided to describe mechanisms adopted to sense the external acidic pH. Particular attention is paid to Escherichia coli extreme acid resistance mechanisms, the activity of which ensure survival and may be directly linked to virulence.
作为其生命周期的一部分，中性菌经常会暴露于各种环境压力中，其中 pH 值波动是最常见的。特别是在发酵食品和动物宿主的胃腔等许多情况下，都会遇到酸性环境。在此，我们综述了一系列革兰氏阳性和革兰氏阴性细菌（主要是影响人类健康的细菌）适应酸应激的分子机制的最新知识。由于有机酸和无机酸会对生物大分子的活性产生有害影响，以至于严重降低生长速度，甚至威胁其生存能力，因此，中性菌进化出了许多不同的保护机制也就不足为奇了，这些机制使它们在其他可能危及生命的条件下具有优势。这些机制的总体逻辑是保护细胞免受有害水平质子的有害影响。最受欢迎的机制包括质子泵出、氨的产生和质子消耗的脱羧反应，以及膜中脂质含量的改变。提供了一些例子来说明用于感知外部酸性 pH 值的机制。特别关注大肠杆菌的极端耐酸性机制，其活性可确保生存，并可能与毒力直接相关。
