Foster J W
Department of Microbiology and Immunology, University of South Alabama, College of Medicine, Mobile 36688, USA.
Crit Rev Microbiol. 1995;21(4):215-37. doi: 10.3109/10408419509113541.
Salmonella typhimurium periodically confronts acid environments during its life. These situations arise in chemically compromised ponds, soil, degradative cellular organelles, host digestive systems, and may even result from byproducts of their own metabolism. The levels of acid that are encountered range from mild to extreme. As a neutralophile, S. typhimurium prefers to grown in pH environments above pH 5.5. They can survive down to pH 4 for extended periods of time. However, the limits of endurance can be stretched if the organisms are first adapted to a moderate acid pH before exposing them to acidity below pH 4.0. This adaptation, called the acid-tolerance response (ATR), includes several log phase and stationary phase systems. Some of these systems are dependent on an alternate sigma factor for RNA polymerase called sigma s, whereas other systems are sigma s-independent. A key to the ATR is the synthesis of a series of acid shock inducible proteins (ASPs), 51 for log phase ATR and 15 for stationary phase ATR. Some of these ASPs require sigma s for their synthesis; others require the participation of the ferric uptake regulator protein Fur. Effective acid tolerance involves RecA-independent DNA repair systems, iron, and facets of fatty acid metabolism. Aspects of medium composition and carbon metabolism are also known to influence the nature of acid tolerance in this organism. In addition to aiding survival in the natural non-host environment, aspects of acid tolerance are also tied to virulence, as evidenced by the involvement of the mouse virulence locus mviA and the fact that acid-sensitive strains of S. typhimurium exhibit reduced virulence. This review summarizes these aspects of acid adaptation and includes a discussion of acid-regulated gene expression.
鼠伤寒沙门氏菌在其生存过程中会周期性地面临酸性环境。这些情况出现在化学性质受到破坏的池塘、土壤、降解性细胞器、宿主消化系统中，甚至可能源于其自身代谢的副产物。所遇到的酸性水平从轻度到极端不等。作为嗜中性菌，鼠伤寒沙门氏菌更喜欢在pH值高于5.5的环境中生长。它们可以在pH值低至4的环境中长时间存活。然而，如果生物体在暴露于pH值低于4.0的酸性环境之前先适应中等酸性pH值，其耐受极限可以被延长。这种适应过程称为耐酸反应（ATR），包括几个对数期和稳定期系统。其中一些系统依赖于一种称为σs的RNA聚合酶的替代σ因子，而其他系统则不依赖于σs。ATR的一个关键是一系列酸休克诱导蛋白（ASP）的合成，对数期ATR有51种，稳定期ATR有15种。其中一些ASP的合成需要σs；其他的则需要铁摄取调节蛋白Fur的参与。有效的耐酸性涉及不依赖RecA的DNA修复系统、铁和脂肪酸代谢的多个方面。培养基组成和碳代谢的一些方面也已知会影响该生物体耐酸性的性质。除了有助于在自然非宿主环境中生存外，耐酸性的一些方面也与毒力相关，如小鼠毒力基因座mviA的参与以及鼠伤寒沙门氏菌的酸敏感菌株毒力降低这一事实所证明。本综述总结了酸适应的这些方面，并包括对酸调节基因表达的讨论。
