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High-cell-density regulation of the Pseudomonas aeruginosa type III secretion system: implications for tryptophan catabolites.
- Source :
-
Microbiology (Reading, England) [Microbiology (Reading)] 2008 Aug; Vol. 154 (Pt 8), pp. 2195-2208. - Publication Year :
- 2008
-
Abstract
- The Pseudomonas aeruginosa type III secretion system (T3SS) is known to be a very important virulence factor in acute human infections, but it is less important in maintaining chronic infections in which T3SS genes are downregulated. In vitro, the activation of T3SS expression involves a positive activating loop that acts on the transcriptional regulator ExsA. We have observed that in vivo T3SS expression is cell density-dependent in a manner that does not need known quorum-sensing (QS) signals. In addition, stationary-phase culture supernatants added to exponential-phase growing strains can inhibit T3SS expression. The analysis of transposon insertion mutants showed that the production of such T3SS-inhibiting signals might depend on tryptophan synthase and hence tryptophan, which is the precursor of signalling molecules such as indole-3-acetic acid (IAA), kynurenine and Pseudomonas quinolone signal (PQS). Commercially available tryptophan-derived molecules were tested for their role in the regulation of T3SS expression. At millimolar concentrations, IAA, 1-naphthalacetic acid (NAA) and 3-hydroxykynurenine inhibited T3SS expression. Inactivation of the tryptophan dioxygenase-encoding kynA gene resulted in a decrease in the T3SS-inhibiting activity of supernatants. These observations suggest that tryptophan catabolites are involved in the downregulation of T3SS expression in the transition from a low- to a high-cell-density state.
- Subjects :
- Bacterial Proteins genetics
Indoleacetic Acids metabolism
Kynurenine analogs & derivatives
Kynurenine metabolism
Mutation
Protein Transport
Pseudomonas aeruginosa genetics
Tryptophan analogs & derivatives
Virulence Factors genetics
Virulence Factors metabolism
Bacterial Proteins metabolism
Gene Expression Regulation, Bacterial
Pseudomonas aeruginosa growth & development
Pseudomonas aeruginosa metabolism
Tryptophan metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 1350-0872
- Volume :
- 154
- Issue :
- Pt 8
- Database :
- MEDLINE
- Journal :
- Microbiology (Reading, England)
- Publication Type :
- Academic Journal
- Accession number :
- 18667553
- Full Text :
- https://doi.org/10.1099/mic.0.2007/013680-0