Jennison Amy V, Verma Naresh K
School of Biochemistry and Molecular Biology, Faculty of Science, The Australian National University, Canberra, Australia.
Microbiology (Reading). 2007 Aug;153(Pt 8):2593-2602. doi: 10.1099/mic.0.2007/006718-0.
The stationary-phase acid-resistance pathways of Shigella flexneri 2457T have not previously been studied. The two acid-resistance systems, the glutamate-dependent acid-resistance (GDAR) and the oxidative pathways, reported elsewhere for Escherichia coli and S. flexneri 3136, were both detected in S. flexneri 2457T. However, S. flexneri 2457T cells grown overnight under fermentative conditions and acid-shocked in minimal media in the absence of glutamate, an acid test often described as a negative control for both pathways, were capable of surviving acid challenge. It is possible that this resistance is due to the oxidative pathway operating in a non-glucose-repressible manner, or to a novel pathway present in S. flexneri 2457T. The construction of gadB and gadC mutants ruled out any contribution by the GDAR pathway, whilst further characterizing the GDAR properties of S. flexneri 2457T. Interestingly, study of the role of rpoS in the oxidative pathway and the unusual acid-resistance phenotype revealed that the frameshift present in the 2457T rpoS gene results in expression of a truncated RpoS protein, which may be reduced in activity and is not essential for the acid-resistance phenotype of S. flexneri 2457T.
弗氏志贺菌2457T的固定相耐酸途径此前尚未得到研究。在大肠杆菌和弗氏志贺菌3136中报道的两种耐酸系统，即谷氨酸依赖型耐酸（GDAR）和氧化途径，在弗氏志贺菌2457T中均被检测到。然而，在发酵条件下过夜培养并在不含谷氨酸的基本培养基中进行酸应激处理（这一酸试验通常被描述为这两种途径的阴性对照）的弗氏志贺菌2457T细胞，能够在酸挑战中存活。这种抗性可能是由于氧化途径以非葡萄糖抑制的方式起作用，或者是由于弗氏志贺菌2457T中存在一种新的途径。gadB和gadC突变体的构建排除了GDAR途径的任何作用，同时进一步表征了弗氏志贺菌2457T的GDAR特性。有趣的是，对rpoS在氧化途径和异常耐酸表型中的作用的研究表明，2457T rpoS基因中存在的移码导致截短的RpoS蛋白表达，其活性可能降低，并且对于弗氏志贺菌2457T的耐酸表型并非必需。
