Comparison of acid stress responses and effects of indole across laboratory, pathogenic, and commensal E. coli

大肠杆菌具有多种耐酸系统，可以保护细胞免受低pH的影响。其中一个系统是AR2，它需要生长介质中存在氨基酸谷氨酸。AR2可以通过将指数期细胞暴露在pH为5.5的环境中30-60分钟来激活。细胞对这种诱导的反应是，当暴露在pH值为2.5或更低的水平时，细胞的存活率增加。在我们的研究中，我们比较了不同的大肠杆菌物种，如常用的K-12实验室菌株-BW25113和MG1655，致病菌株O157：H7和益生菌Nissle 1917，当暴露在pH 2.5的极端酸胁迫下时，在不同的生长阶段，如指数期、指数后期和稳定期，它们的AR2系统被诱导和不被诱导，它们的存活率进行了比较。此外，我们正在研究细菌信号分子吲哚如何通过直接或间接与EvgAS结合来抑制AR2系统的诱导，EvgAS是参与AR2系统诱导的两个组成系统之一。

Escherichia coli (E. coli) has multiple acid resistance systems which protect the cells against low pH. One of these systems is AR2, which requires the presence of amino acid glutamate in the growth media. AR2 can be activated by exposing exponential phase cells to a pH of 5.5 for 30-60 mins. Cells respond to this induction by showing increased levels of survival upon exposure to pH levels of 2.5 and below. In our study we are comparing the survival of different E. coli species such as commonly used K-12 lab strains- BW25113 and MG1655, the pathogenic strain O157:H7 and a probiotic strain Nissle 1917, when exposed to extreme acid stress at pH 2.5 with and without their AR2 system being induced at different growth stages such as exponential, late-exponential, and stationary phase. Furthermore, we are examining how the bacterial signalling molecule indole can inhibit the induction of AR2 system by either directly or indirectly binding to EvgAS, one of the two component systems involved in induction of AR2 system.