A POSITIVE REGULATORY GENE, PVDS, FOR EXPRESSION OF PYOVERDIN BIOSYNTHETIC GENES IN PSEUDOMONAS-AERUGINOSA PAO

In response to iron limitation Pseudomonas aeruginosa PAO induces production of pyoverdin, a low-molecular-weight siderophore able to capture ferric ion with a very high affinity. The pvd genes involved in the pyoverdin biosynthesis are organized in a chromosomal region termed the pvd region, and expression of some pvn genes is regulated at the transcriptional level. Two sets of promoter regions for the pvd genes were defined that were transcriptionally derepressed under iron-limiting conditions. Analysis of transcription from such promoters in Escherichia coli led to isolation and identification of a positive regulatory, gene, pvdS, for expression of the pvd genes, and pvdS was localized in the pvd region. A genomic pvdS mutant of PAO, constructed by allelic exchange mutagenesis, produced no pyoverdin and did not allow transcription from the pvd promoters. Nucleotide sequence analysis revealed that PvdS shows considerable similarity to FecI of E. coli, a positive regulator for transcription of the fec (ferric citrate transport system) operon. The promoter region of pvdS has the sequence that matches well the consensus binding site for the E. coli Fur protein, a global negative regulatory protein that represses the transcription of the iron repressible genes. Consistent with the presence of such a consensus sequence, addition of iron repressed transcription of the pvdS gene in P. aeruginosa.