IDENTIFICATION AND CHARACTERIZATION OF A SIDEROPHORE REGULATORY GENE (PFRA) OF PSEUDOMONAS-PUTIDA WCS358 - HOMOLOGY TO THE ALGINATE REGULATORY GENE ALGQ OF PSEUDOMONAS-AERUGINOSA

Genes encoding biosynthesis of pseudobactin 358 (a microbial iron tran sport agent) and its cognate outer membrane receptor protein, PupA, ar e transcribed only under iron limitation in plant growth-promoting Pse udomonas putida WCS358. Two cosmid clones were identified from a gene bank of WCS358 DNA which could independently and in an iron-dependent manner activate transcription from a WCS358 siderophore gene promoter in heterologous Pseudomonas strain A225. The functional region of one of the clones was localized by subcloning, transposon Tn3Gus mutagenes is, and DNA sequencing. Genomic transposon insertion mutants in the fu nctional region lost the capacity to activate a siderophore gene promo ter fusion transcriptionally; furthermore, these mutants no longer pro duced pseudobactin 358. The activating region consisted of a single ge ne designated pfrA (Pseudomonas ferric regulator). The pfrA gene codes for a single polypeptide, PfrA, of approximately 18 kDa, which has 58 % identity to AlgQ (also known as AlgR2), a positive regulator involve d in transcriptionally regulating alginate biosynthesis in Pseudomonas aeruginosa. Cross-complementation studies between the pfrA gene of P. putida and the algQ gene of P. aeruginosa revealed that pfrA can rest ore mucoidy (alginate production) in an algQ mutant and that algQ coul d poorly complement a pfrA genomic mutant. It is concluded that PfrA i s involved in the positive regulation of siderophore biosynthetic gene s in response to iron limitation; furthermore, pfrA and algQ appeared to be interchangeable between P. putida and P. aeruginosa.