Pseudomonas aeruginosa controls the secretion of extracellular virulence factors, including rhamnolipids and LasB elastase, by the las and rhl quorum-sensing systems. Here, we mutated the dksA gene of P. aeruginosa by insertion of an ⍀-Hg cassette. The mutant displayed growth rates similar to that of the wild type in rich medium but was impaired in growth in defined minimal medium. Production of rhamnolipids and LasB elastase by the dksA mutant was only 4 and 10%, respectively, of wild-type levels. These defects could be partially complemented by introduction of the plasmid-encoded dksA genes from P. aeruginosa or Escherichia coli. In the dksA mutant, the expression of rhlI was increased early during exponential growth, but expression of other quorum-sensing regulator genes-lasR, lasI, and rhlR-was not affected. Although the transcription of the lasB and rhlAB genes was comparable between the dksA mutant and the wild-type strain in peptone tryptic soy broth medium, we observed reduced translation of both genes in the dksA mutant. Similarly, we found that full translation of lasB and rhlAB genes in E. coli also requires the dksA gene. DksA is therefore a novel regulator involved in the posttranscriptional control of extracellular virulence factor production in P. aeruginosa.The opportunistic pathogen Pseudomonas aeruginosa is responsible for severe nosocomial infections in immunocompromised and intubated patients (4). In addition, P. aeruginosa is the most commonly found pathogen in cystic fibrosis (CF) patients and is responsible for progressive lung tissue destruction leading to respiratory failure (4). P. aeruginosa produces a wide spectrum of secreted virulence factors, including LasB elastase, rhamnolipids, pyocyanin, lipase, and hydrogen cyanide (30). The las and rhl quorum-sensing systems regulate the production of these factors in a cell density-dependent manner. This regulation relies on the accumulation in the medium of two autoinducer (AI) molecules, 3-oxo-C 12 -homoserine lactone (3-oxo-C 12 -HSL) and C 4 -HSL, that induce the las and rhl quorum-sensing systems when the bacterial cell density reaches a certain threshold (quorum), leading to transcription of specific genes and the production of the virulence factors cited above. Both systems involve a transcriptional regulator (RhlR and LasR, respectively) and an AI synthase (RhlI and LasI, respectively) (30). A hierarchy was proposed in which the las system activates the rhl system by inducing the transcription of the activator gene rhlR (12,20).Additional layers of regulation of the quorum-sensing circuitry have been described. These include the transcriptional regulator vfr (1), a homologue of the Escherichia coli cyclic AMP-binding protein, the GacA two-component regulator (23), the enzyme polyphosphate kinase (22), and the mvaT gene product which modulates the timing of quorum-sensing activation (5). Recently, we have shown that overexpression of the starvation response regulator encoded by relA, leading to increased production of the nutrient str...

Tributyltin (TBT) is a toxic agent used in marine antifouling paints. Among the bacterial flora of a polluted harbor, TBT-resistant strains of Pseudomonas stutzeri have been isolated. In the strain 5MP1 (TBT minimum inhibitory concentration (MIC) v 1000 mg l 31 ), TBT resistance was found to be associated with the presence of the operon tbtABM, homologous to the resistance^nodulation^cell division (RND) efflux pump family, as demonstrated by cloning in Escherichia coli. TbtABM exhibited the greatest homology (60.98 4.9%) with the TtgDEF and SrpABC systems, both involved in aromatic compound tolerance in P. putida. TbtABM conferred multidrug resistance (MDR) including to n-hexane, nalidixic acid, chloramphenicol, and sulfamethoxazole (antibiotic MICsU4 for the E. coli host strain carrying the operon). By polymerase chain reaction amplification and hybridization experiments, the presence of tbtABM was detected in the TBT-sensitive P. stutzeri 3MP1 (TBT MIC 25 mg l 31 ). However, the latter strain did not seem to express TbtABM. This is the first description of a MDR efflux pump in P. stutzeri, and of a new kind of substrate, TBT, for the RND family of transporters.