Motility-activating mutations upstream of flhDC reduce acid shock survival of Escherichia coli
Many neutralophilic bacterial species try to evade acid stress with an escape strategy, which is reflected in the increased expression of genes coding for flagellar components. Extremely acid-tolerant bacteria, such as Escherichia coli, survive the strong acid stress, e.g. in the stomach of vertebrates. Recently, we were able to show that the induction of motility genes in E. coli is strictly dependent on the degree of acid stress, i.e. they are induced under mild acid stress but not under severe acid stress. However, it was not known to what extent fine-tuned expression of motility genes is related to fitness and the ability to survive periods of acid shock. In this study, we demonstrate that the expression of FlhDC, the master regulator of flagellation, is inversely correlated with acid shock survival of E. coli. We encountered this phenomenon when analyzing mutants from the Keio collection in which the expression of flhDC was altered by an IS element. These results suggest a fitness trade-off between acid tolerance and motility. Overall design: Comparison of genome-wide mRNA levels in E. coli MG1655 WT and dmhpR, as well as BW25113 and BW25113 mhpR::km (Keio collection) at pH 4.4 in LB medium.