I. Cases et al., Role of ptsO in carbon-mediated inhibition of the Pu promoter belonging tothe pWWO Pseudomonas putida plasmid, J BACT, 183(17), 2001, pp. 5128-5133
An investigation was made into the role of the ptsO gene in carbon source i
nhibition of the Pu promoter belonging to the Pseudomonas putida upper TOL
(toluene degradation) operon. ptsO is coexpressed with ptsN, the loss of wh
ich is known to render Pu unresponsive to glucose. Both ptsN and ptsO, codi
ng for the phosphoenolpyruvate:sugar phosphotransferase system (PTS) family
proteins IIA(Ntr) and NPr, respectively, have been mapped adjacent to the
rpoN gene of P. putida. The roles of these two genes in the responses of Pu
to glucose were monitored by lacZ reporter technology with a P. putida str
ain engineered with all regulatory elements in monocopy gene dosage. In cel
ls lacking ptsO, Pu activity seemed to be inhibited even in the absence of
glucose. A functional relationship with ptsN was revealed by the phenotype
of a double ptsN ptsO mutant that was equivalent to the phenotype of a muta
nt with a single ptsN disruption. Moreover, phosphorylation of the product
of ptsO seemed to be required for C inhibition of Pu, since an H15A change
in the NPr sequence that prevents phosphorylation of this conserved amino a
cid residue did not restore the wild-type phenotype. A genomic search for p
roteins able to phosphorylate ptsO revealed the presence of two open readin
g frames, designated ptsP and mtp, with the potential to encode PTS type I
enzymes in P. putida. However, neither an insertion in ptsP nor an insertio
n in mtp resulted in a detectable change in inhibition of Pu by glucose. Th
ese results indicate that some PTS proteins have regulatory functions in P.
putida that are independent of their recognized role in sugar transport in
other bacteria.