Transcriptional regulation of pseudobactin synthesis in the plant growth-promoting Pseudomonas B10.

We have investigated the iron-dependent regulation of the psbA gene, encoding the enzyme L-ornithine N(5)-oxygenase in the rhizobacterium Pseudomonas B10. We have cloned and characterized a Pseudomonas B10 gene, designated psbS, required for psbA expression. PsbS is endowed with structural and functional features of extracytoplasmatic function (ECF) sigma factors, and is closely related to the iron starvation sigmas PvdS, PbrA, and PfrI, which mediate the iron-repressible expression of pseudobactin biosynthesis genes in different Pseudomonas species. Expression of psbA was found to be indirectly controlled by Fur, which abrogates psbS transcription in the presence of sufficient iron.