ALGINATE REGULATORY AND BIOSYNTHETIC GENE HOMOLOGS IN PSEUDOMONAS-PUTIDA WCS358 - CORRELATION WITH THE SIDEROPHORE REGULATORY GENE PFRA

A previous study [Venturi et al., Mol. Microbiol. 10 (1993) 63-73] dem onstrated that the siderophore regulatory gene pfrA of Pseudomonas put ida (Pp) WCS358 is highly similar and interchangeable with the alginat e regulatory gene algQ (algR2) of P. nel aeruginosa (Pa). The algQ gen e is physically linked to two other alginate regulators in the Pa chro mosome, namely algR (algR1), a response regulator, and algP (algR3), a histone-like gene. In this study, we have identified the same genes a nd a similar genetic organization in the Pp chromosome. The two genes linked to pfrA, designated pprA and pprB, are similar to algR and algP , respectively. Chromosomal mutants of pprA and pprB were constructed showing that unlike pfrA, the two newly identified regulators are not involved in siderophore regulation. The pprA gene complemented a Pa al gR mutant phenotype, suggesting that it could be involved in alginate gene regulation The WCS358 strain is not producing alginate, but we de monstrated by Southern analysis that it also possesses, in addition to pprA and pprB, algD and algU (algT) gene homologs, two genes essentia l for alginate biosynthesis. Using an algD-xylE transcriptional fusion , we observed that the algD promoter is active in strain WCS358 and ab solutely requires pfrA. The possibility that all five genes of Pp WCS3 58 are involved in alginate biosynthesis is discussed.