Sigma Factor RpoS Controls Alkylresorcinol Synthesis through ArpR, a LysR-Type Regulatory Protein, during Encystment of Azotobacter vinelandii

Azotobacter vinelandii is a bacterium which undergoes a differentiation process leading to the formation of metabolically dormant cysts. During the encystment process,A. vinelandii produces alkylresorcinol lipids (ARs) that replace the membrane phospholipids and are also components of the layers covering the cyst. The synthesis of ARs inA. vinelandii has been shown to occur by the activity of enzymes encoded by thearsABCD operon, which is expressed only during the differentiation process. Also, the production of ARs has been shown to be dependent on the stationary-phase sigma factor RpoS, which is also implicated in the control of the synthesis of other cyst components (i.e., alginate and poly-β-hydroxybutyrate). In this study, we identified ArpR, a LysR-type transcriptional regulator expressed only during encystment that positively regulatesarsABCD transcription. We show that this activation is dependent on acetoacetyl-coenzyme A (acetoacetyl-CoA), which might provide a metabolic signal for encystment. We also show that RpoS regulatesarsABCD expression through the control ofarpR transcription.