[WCB-7] tnaA mRNAの特異的分解を介した大腸菌の酸耐性発現機構
Acid-resistance systems are essential for pathogenic Escherichia coli to survive in the strongly acidic environment of the human stomach (pH<2.5). Among the five primary systems defined to date, the glutamic acid decarboxylase (GAD) system is the most effective. Our RNA-sequencing analysis of gene expression profiles upon acid treatment revealed that tnaA mRNA levels drastically decreased upon exposure to moderately acidic condition (pH 5.5). The tnaA gene encodes tryptophanase, which is solely responsible for the production of indole. Deletion of tnaA induced the GAD expression even under neutral pH, which was suppressed by the addition of indole to the growth medium. These results suggested that indole negatively regulates the GAD expression. The decrease in tnaA mRNA levels upon the pH shift was suppressed by RNase E deficiency, suggesting that tnaA mRNA is specifically degraded via cleavage catalyzed by RNase E under acidic conditions. Collectively, this study demonstrates that the RNase E-dependent degradation of tnaA mRNA is accelerated upon acid exposure, which decreases intracellular indole concentrations to trigger the GAD expression.