Castanie-Cornet M P, Penfound T A, Smith D, Elliott J F, Foster J W
Department of Microbiology and Immunology, University of South Alabama College of Medicine, Mobile, Alabama 36688, USA.
J Bacteriol. 1999 Jun;181(11):3525-35. doi: 10.1128/JB.181.11.3525-3535.1999.
Acid resistance (AR) in Escherichia coli is defined as the ability to withstand an acid challenge of pH 2.5 or less and is a trait generally restricted to stationary-phase cells. Earlier reports described three AR systems in E. coli. In the present study, the genetics and control of these three systems have been more clearly defined. Expression of the first AR system (designated the oxidative or glucose-repressed AR system) was previously shown to require the alternative sigma factor RpoS. Consistent with glucose repression, this system also proved to be dependent in many situations on the cyclic AMP receptor protein. The second AR system required the addition of arginine during pH 2.5 acid challenge, the structural gene for arginine decarboxylase (adiA), and the regulator cysB, confirming earlier reports. The third AR system required glutamate for protection at pH 2.5, one of two genes encoding glutamate decarboxylase (gadA or gadB), and the gene encoding the putative glutamate:gamma-aminobutyric acid antiporter (gadC). Only one of the two glutamate decarboxylases was needed for protection at pH 2.5. However, survival at pH 2 required both glutamate decarboxylase isozymes. Stationary phase and acid pH regulation of the gad genes proved separable. Stationary-phase induction of gadA and gadB required the alternative sigma factor sigmaS encoded by rpoS. However, acid induction of these enzymes, which was demonstrated to occur in exponential- and stationary-phase cells, proved to be sigmaS independent. Neither gad gene required the presence of volatile fatty acids for induction. The data also indicate that AR via the amino acid decarboxylase systems requires more than an inducible decarboxylase and antiporter. Another surprising finding was that the sigmaS-dependent oxidative system, originally thought to be acid induced, actually proved to be induced following entry into stationary phase regardless of the pH. However, an inhibitor produced at pH 8 somehow interferes with the activity of this system, giving the illusion of acid induction. The results also revealed that the AR system affording the most effective protection at pH 2 in complex medium (either Luria-Bertani broth or brain heart infusion broth plus 0.4% glucose) is the glutamate-dependent GAD system. Thus, E. coli possesses three overlapping acid survival systems whose various levels of control and differing requirements for activity ensure that at least one system will be available to protect the stationary-phase cell under naturally occurring acidic environments.
大肠杆菌中的耐酸性(AR)被定义为耐受pH 2.5及以下酸性挑战的能力,这一特性通常仅限于稳定期细胞。早期报告描述了大肠杆菌中的三种AR系统。在本研究中,这三种系统的遗传学和调控机制得到了更清晰的界定。先前已证明,第一个AR系统(称为氧化或葡萄糖抑制的AR系统)的表达需要替代sigma因子RpoS。与葡萄糖抑制一致,该系统在许多情况下也被证明依赖于环腺苷酸受体蛋白。第二个AR系统在pH 2.5酸性挑战期间需要添加精氨酸、精氨酸脱羧酶(adiA)的结构基因以及调节因子cysB,这证实了早期报告。第三个AR系统在pH 2.5时需要谷氨酸进行保护、两个编码谷氨酸脱羧酶的基因之一(gadA或gadB)以及编码假定的谷氨酸:γ-氨基丁酸反向转运体的基因(gadC)。在pH 2.5时进行保护仅需要两种谷氨酸脱羧酶中的一种。然而,在pH 2时存活需要两种谷氨酸脱羧酶同工酶。已证明,gad基因的稳定期和酸性pH调控是可分离的。gadA和gadB的稳定期诱导需要由rpoS编码的替代sigma因子sigmaS。然而,这些酶的酸性诱导(已证明在指数期和稳定期细胞中都会发生)被证明不依赖于sigmaS。两个gad基因的诱导均不需要挥发性脂肪酸的存在。数据还表明,通过氨基酸脱羧酶系统实现的AR需要的不仅仅是一种可诱导的脱羧酶和反向转运体。另一个惊人的发现是,最初被认为是酸诱导的依赖sigmaS的氧化系统,实际上被证明是在进入稳定期后被诱导的,而与pH无关。然而,在pH 8时产生的一种抑制剂以某种方式干扰了该系统的活性,造成了酸诱导的假象。结果还表明,在复合培养基(无论是Luria-Bertani肉汤还是脑心浸液肉汤加0.4%葡萄糖)中,在pH 2时提供最有效保护的AR系统是依赖谷氨酸的GAD系统。因此,大肠杆菌拥有三种重叠的酸存活系统,其不同的调控水平和对活性的不同要求确保在自然发生的酸性环境下至少有一个系统可用于保护稳定期细胞。