CLONING AND CHARACTERIZATION OF PVDS, A GENE REQUIRED FOR PYOVERDINE SYNTHESIS IN PSEUDOMONAS-AERUGINOSA - PVDS IS PROBABLY AN ALTERNATIVE SIGMA-FACTOR

Cells of Pseudomonas aeruginosa secrete a fluorescent yellow-green sid erophore, pyoverdine, when grown under iron deficient conditions, We d escribe here the cloning and characterization of a gene, pvdS, which i s required for this process, The pvdS gene is required for expression from promoters of at least two pyoverdine synthesis genes and can caus e expression from these promoters in Escherichia coil, where they are otherwise inactive, Sequencing of pvdS revealed that it is a member of a subfamily of RNA polymerase sigma factors which direct the synthesi s of extracellular products by bacteria, The pvdS gene is expressed on ly in iron-starved bacteria, and in E. coli cells at least, expression is regulated by the Fur repressor protein, We propose that in iron-ri ch cells of P. aeruginosa, Fur binds to the pvdS promoter and prevents expression of the gene; under conditions of iron starvation, repressi on is relieved and PvdS is made, reprogramming the cells for pyoverdin e synthesis.