GacA regulates the PTSNtr-dependent control of cyst formation in Azotobacter vinelandii

Azotobacter vinelandii forms cysts resistant to desiccation and produces polyhydroxybutyrate (PHB), alginate and alkylresorcinols (ARs) that are components of mature cysts. The expression of genes involved in the synthesis of these compounds is under the control of the GacA-RsmA global regulatory system where the RsmA protein represses the translation of mRNAs involved in the synthesis of these polymers. The synthesis of PHB and ARs is also controlled by the Nitrogen-regulated phosphotransferase system (PTS^Ntr) global regulatory system. When unphosphorylated, the Enzyme IIA^Ntr (EIIA^Ntr) protein impairs the synthesis of PHB and ARs. Here we show that cells of gacA mutants, as well as mutants that carry the EIIA^Ntr protein in its unphosphorylated state, have similar encysting negative phenotypes. Interestingly, we found that in the gacA mutant strain, the EIIA^Ntr protein was present in its unphosphorylated state. These data indicated that in addition to the GacA-RsmA system, GacA controls polymer synthesis and encystment by controlling the phosphorylation of the EIIA^Ntr, revealing a previously unrecognized link between GacA and PTS^Ntr.