Regassa L B, Betley M J
University of Wisconsin-Madison 53706.
J Bacteriol. 1992 Aug;174(15):5095-100. doi: 10.1128/jb.174.15.5095-5100.1992.
The effect of alkaline pH on expression of the accessory gene regulator (agr) in Staphylococcus aureus was examined. agr, a global regulator, affects the expression of numerous exoproteins, including alpha-hemolysin, toxic shock syndrome toxin 1, protein A, and staphylococcal enterotoxins types B, C, and D. agr contains two major, divergent transcripts, designated RNAII and RNAIII. In this study, the level of RNAIII was used to monitor agr expression because this transcript and/or its protein product(s) appears to be responsible for altering target gene expression. S. aureus FRI1230 and its Agr- derivative were examined in a fermentor system which allowed batch cultures to be maintained at a constant pH. FRI1230 cultures were grown at pH 6.5, 7.0, 7.5, and 8.0. Northern (RNA blot) analysis of samples revealed that maximal agr expression occurred at pH 7.0, with virtually no RNAIII observed at pH 8.0. The effect of alkaline pH on an agr target gene, sec, was also evaluated. sec expression was reduced at alkaline pH in strain FRI1230 (Agr+) but not in its Agr- derivative, indicating that an intact agr allele is required for the pH effect on sec. Examination of batch cultures under conditions of nonmaintained pH gave results that were also consistent with a role for alkaline pH in repressing agr expression.
研究了碱性pH对金黄色葡萄球菌中辅助基因调节因子（agr）表达的影响。agr作为一种全局调节因子，影响多种胞外蛋白的表达，包括α-溶血素、中毒性休克综合征毒素1、蛋白A以及B型、C型和D型葡萄球菌肠毒素。agr包含两个主要的、不同的转录本，分别命名为RNAII和RNAIII。在本研究中，使用RNAIII的水平来监测agr的表达，因为该转录本和/或其蛋白质产物似乎负责改变靶基因的表达。在一个发酵罐系统中对金黄色葡萄球菌FRI1230及其Agr - 衍生物进行了检测，该系统可使分批培养物维持在恒定的pH值。FRI1230培养物在pH 6.5、7.0、7.5和8.0的条件下生长。对样品进行的Northern（RNA印迹）分析表明，agr的最大表达发生在pH 7.0时，在pH 8.0时几乎未观察到RNAIII。还评估了碱性pH对agr靶基因sec的影响。在碱性pH条件下，FRI1230菌株（Agr +）中的sec表达降低，但其Agr - 衍生物中的sec表达未降低，这表明完整的agr等位基因是pH对sec产生影响所必需的。在非维持pH条件下对分批培养物进行检测，所得结果也与碱性pH在抑制agr表达中所起的作用一致。
