Unphosphorylated EIIA induces ClpAP-mediated degradation of RpoS in Azotobacter vinelandii.

The nitrogen-related phosphotransferase system (PTS ) is composed of the EI , NPr and EIIA proteins that form a phosphorylation cascade from phosphoenolpyruvate. PTS is a global regulatory system present in most Gram-negative bacteria that controls some pivotal processes such as potassium and phosphate homeostasis, virulence, nitrogen fixation and ABC transport activation. In the soil bacterium Azotobacter vinelandii, unphosphorylated EIIA negatively regulates the expression of genes related to the synthesis of the bioplastic polyester poly-β-hydroxybutyrate (PHB) and cyst-specific lipids alkylresorcinols (ARs). The mechanism by which EIIA controls gene expression in A. vinelandii is not known. Here, we show that, in presence of unphosphorylated EIIA , the stability of the stationary phase sigma factor RpoS, which is necessary for transcriptional activation of PHB and ARs synthesis related genes, is reduced, and that the inactivation of genes coding for ClpAP protease complex in strains that carry unphosphorylated EIIA , restored the levels and in vivo stability of RpoS, as well as the synthesis of PHB and ARs. Taken together, our results reveal a novel mechanism, by which EIIA globally controls gene expression in A. vinelandii, where the unphosphorylated EIIA induces the degradation of RpoS by the proteolytic complex ClpAP.