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- Title
Molecular characterization of mutants affected in the osmoprotectant-dependent induction of phospholipase C in <em>Pseudomonas aeruginosa</em> PAO1.
- Authors
Sage, Andrew E.; Vasil, Adriana I.; Vasil, Michael L.
- Abstract
Production of the two phospholipases C (PLCs) in <em>Pseudomonas aeruginosa</em> PAO1 is induced under conditions of phosphate limitation, or by the osmoprotectants choline or glycine betaine. Tn5 mutagenesis was performed on strain PAO1 to isolate mutants deficient in choline-dependent induction of PLC. Two mutants, Tn5T1 and Tn5G19, were identified which produce decreased levels of PLC in phosphate-replete media supplemented with choline. A total of 136 and 496 bp of flanking DNA from Tn5G19 and Tn5T1 was cloned by an inverse polymerase chain reaction (PCR) and sequenced. The DNA flanking the Tn5T1 insertion contains an open reading frame predicted to encode a peptide that is approx. 60% identical to the N-terminus of a previously identified protein (P35) of unknown function from <em>Escherichia coli</em>. The P35 gene, which is located in the <em>nusA-infB</em> operon in <em>E. coli</em>, was designated orp (osmoprotectant regulator of PLC). Haemolytic titres, total PIcH protein and β-galactosidase activity expressed from a chromosomally inserted <em>plcH-lacZ</em> operon fusion were reduced in strain Tn5T1 in comparison with the parental strain (PAO1) carrying the same fusion. However, this mutant expressed several-fold higher levels of <em>plcH</em> message than strain PAO1 in the presence of choline, while the phosphate-starvation-dependent transcript of <em>plcH</em> could not be detected in this mutant. The defects in Tn5T1 are complemented by a DNA fragment, isolated from a genomic library of PAO1, that carries the <em>orp</em> gene. The deduced amino acid sequence of the DNA fragment cloned from Tn5G19 exhibits 84% identity with the betB gene product of <em>E. coli</em> that has betaine aldehyde dehydrogenase activity. This enzyme catalyses the conversion of betaine aldehyde to glycine-betaine. Unlike the parental strain, the Tn5G19 mutant could not utilize choline as a sole carbon, nitrogen and energy source, and it was deficient in betaine aldehyde dehydrogenase activity. Also, consistent with a disruption of <em>betB</em> in Tn5G19, choline inhibited growth of this strain in media containing 0.7M NaCl, while glycine-betaine restores growth to wild-type levels. The defects in Tn5G19 are complemented by a DNA fragment from PAO1 that carries the <em>betB</em> gene. The <em>orp</em> gene is located between 0.6 to 6.6 min while <em>betB</em> is located between 10.5 to 12.5 min on the chromosome of PAO1.
- Subjects
PHOSPHOLIPASES; PSEUDOMONAS aeruginosa; CHOLINE; MUTAGENESIS; PEPTIDES
- Publication
Molecular Microbiology, 1997, Vol 23, Issue 1, p43
- ISSN
0950-382X
- Publication type
Article
- DOI
10.1046/j.1365-2958.1997.1681542.x