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.