LiaRS-dependent gene expression is embedded in transition state regulation in Bacillus subtilis.

Maintaining envelope integrity is crucial for the survival of any bacterial cell, especially those living in a complex and ever-changing habitat such as the soil ecosystem. The LiaRS two-component system is part of the regulatory network orchestrating the cell-envelope stress response in Bacillus subtilis. It responds to perturbations of the cell envelope, especially the presence of antibiotics that interfere with the lipid II cycle, such as bacitracin or vancomycin. LiaRS-dependent regulation is strictly repressed by the membrane protein LiaF in the absence of inducing conditions. Here, it is shown that the LiaR-dependent liaI promoter is induced at the onset of stationary phase without addition of exogenous stresses. Its activity is embedded in the complex regulatory cascade governing adaptation at the onset of stationary phase. The liaI promoter is directly repressed by the transition state regulator AbrB and responds indirectly to the activity of Spo0A, the master regulator of sporulation. The activity of the liaI promoter is therefore tightly regulated by at least five regulators to ensure an appropriate level of liaIH expression.