Abstract
Upon encystment induction, Azotobacter vinelandii produces the phenolic lipids alkylresorcinols (ARs) that are structural components of the cysts. The enzymes responsible for the ARs synthesis are encoded in the arsABCD operon, whose expression is activated by ArpR. The transcription of arpR is initiated from an RpoS dependent promoter. The nitrogen-related phosphotransferase system (PTSNtr) is a global regulatory system present in Gram negative bacteria. It comprises the EINtr, NPr and EIIANtr proteins encoded by ptsP, ptsO and ptsN genes respectively. These proteins participate in a phosphoryl-group transfer from phosphoenolpyruvate to protein EIIANtr via the phosphotransferases EINtr and NPr. In A. vinelandii, the non-phosphorylated form of EIIANtr was previously shown to repress the synthesis of poly-ß-hydroxybutyrate. In this work, we show that PTSNtr also regulates the synthesis of ARs. In a strain that carries unphosphorylated EIIANtr, the expression of arpR was reduced, while synthesis of ARs and transcription of arsA were almost abrogated. The expression of arpR from an RpoS-independent promoter in this strain restored the ARs synthesis. Taken together these results indicate that unphosphorylated EIIANtr negatively affects activation of arpR transcription by RpoS.
Highlights
Azotobacter vinelandii is a soil bacterium that undergoes a differentiation process resulting in the formation of a desiccation resistant cyst
According to the phosphorylation cascade proposed for the PTSNtr [15] the ptsP and ptsO inactivations are expected to impair the phosphorylation of EIIANtr, the unphosphorylated form of EIIANtr could be involved in the negative effect observed on ARs synthesis
A similar effect was observed in BBOH liquid medium; the RpoS-independent expression of arpR increased the AR levels in the strain UW136::pALA8a (Fig. 5B). These results suggest that negative effect of unphosphorylated EIIANtr on arpR expression is due to a negative effect on its transcriptional activation by RpoS
Summary
Azotobacter vinelandii is a soil bacterium that undergoes a differentiation process resulting in the formation of a desiccation resistant cyst. A mature cyst consists of a contracted cell, known as the central body, which is surrounded by a capsule made up of a laminated outer layer called the exine and an inner layer called the intine [1]. The polysaccharide alginate is a major component of the capsule layers. Other components of the cysts are the reserve polyester poly-ßhydroxybutyrate (PHB), that is present in the central body forming large granules, and the phenolic lipids alkylresorcinols (ARs), which replace the membrane phospholipids in the cyst and PLOS ONE | DOI:10.1371/journal.pone.0117184. PTSNtr and Alkylresorcinol Synthesis are components of the exine [2]. Encystment can be induced by transferring log-phase vegetative cells to Burk’s minimal medium with either n-butanol or ß-hydroxybutyrate as the sole carbon source [3]
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