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

大肠杆菌（E.大肠杆菌）具有多种抗酸系统，其保护细胞免受低pH的影响。这些系统之一是AR 2，其需要在生长培养基中存在氨基酸谷氨酸。AR 2可以通过将指数期细胞暴露于pH 5.5持续30-60分钟来活化。细胞通过暴露于2.5及以下的pH水平时显示出增加的存活水平来响应这种诱导。在我们的研究中，我们比较了不同E。大肠杆菌物种，如常用的K-12实验室菌株-BW 25113和MG 1655，致病菌株O 157：H7和益生菌菌株Nissle 1917，当暴露于pH 2.5的极端酸胁迫时，在不同的生长阶段，如指数期、指数后期和稳定期，诱导和不诱导它们的AR 2系统。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结合参与AR 2系统诱导的两个组成系统之一EvgAS来抑制AR 2系统的诱导。

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.