The lysine-dependent acid stress response system in Escherichia coli protects the cells under moderately acidic conditions. It consists of LdcI, the inducible lysine decarboxylase and CadB, the lysine-cadaverine antiporter. LdcI interacts with both ppGpp, the signalling molecule in the stringent response, and RavA, a MoxR-family AAA+ protein induced in the stationary phase. Experiments in vitro have shown that ppGpp inhibits the activity of LdcI and that the interaction between LdcI and RavA antagonizes the inhibition. In this work, it was demonstrated, by using a media shift assay, that the antagonistic regulation of RavA and ppGpp of LdcI activity also takes place in vivo, thereby linking acid resistance to the stringnent response. As part of this study, components of the lysine decarboxylase pathway and the ravA-viaA operon were endogenously tagged with fluorescent proteins. These strains are useful tools to study the localization behaviour of these proteins under different stress conditions.

The lysine-dependent acid stress response system in Escherichia coli protects the cells under moderately acidic conditions. It consists of LdcI, the inducible lysine decarboxylase and CadB, the lysine-cadaverine antiporter. LdcI interacts with both ppGpp, the signalling molecule in the stringent response, and RavA, a MoxR-family AAA+ protein induced in the stationary phase. Experiments in vitro have shown that ppGpp inhibits the activity of LdcI and that the interaction between LdcI and RavA antagonizes the inhibition. In this work, it was demonstrated, by using a media shift assay, that the antagonistic regulation of RavA and ppGpp of LdcI activity also takes place in vivo, thereby linking acid resistance to the stringnent response. As part of this study, components of the lysine decarboxylase pathway and the ravA-viaA operon were endogenously tagged with fluorescent proteins. These strains are useful tools to study the localization behaviour of these proteins under different stress conditions.