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

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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.