Molecular analysis of the Pseudomonas aeruginosa regulatory genes ptxR andptxS

We have previously described two Pseudomonas aeruginosa genes, ptxR, which enhances toxA and pvc ( the pyoverdine chromophore operon) expression, and ptxS, the first gene of the kgu operon for the utilization of 2-ketoglucona te by P. aeruginosa. ptxS interferes with the effect of ptxR on toxA expres sion. In this study, we have utilized DNA hybridization experiments to dete rmine the presence of ptxR and ptxS homologous sequences in several gram-ne gative bacteria. ptxR homologous sequences were detected in P. aeruginosa s trains only, while ptxS homologous sequences were detected in P. aeruginosa , Pseudomonas putida, and Pseudomonas fluorescens. Using Northern blot hybr idization experiments and a ptxS-lacZ fusion plasmid, we have shown that P. aeruginosa ptxR and ptxS are expressed in P. putida and P. fluorescens. Ad ditional Northern blot hybridization experiments confirmed that ptxS is tra nscribed in P. putida and P. fluorescens strains that carried no plasmid. T he presence of a PtxS homologue in these strains was examined by DNA-gel sh ift experiments. Specific gel shift bands were detected when the lysates of P. aeruginosa, P. putida, and P. fluorescens were incubated with the ptxS operator site as probe. kgu-hybridizing sequences were detected in P. putid a and P. fluorescens. These results suggest that (i) ptxR is present in P. aeruginosa, while ptxS is present in P. aeruginosa, P. putida, and P. fluor escens; (ii) both ptxR and ptxS are expressed in P. putida and P. fluoresce ns; and (iii) a PtxS homologue may exist in P. putida and P. fluorescens.