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The ceplR genes encode an N-acyl homoserine lactone (AHL)-dependent quorum-sensing system consisting of an AHL synthase that directs the synthesis of N-octanoyI-L-homoserine lactone (OHL) and N-hexanoyI-L-homoserine lactone and a transcriptional regulator. The virulence of cepIR mutants was examined in two animal models. Rats were infected with agar beads containing Burkholderia cenocepacia K56-2, K56-12 (cepl: :[Tp.sup.r]) or K56-R2 (cepR'' Tn5-OT182). At 10 days post-infection, the extent of lung histopathological changes was significantly lower in lungs infected with K56-12 or K56-R2 compared to the parent strain. Intranasal infections were performed in [Cftr.sup.(-/-)] mice and their wild-type siblings. K56-2 was more virulent in both groups of mice. K56-12 was the least virulent strain and was not invasive in the [Cftr.sup.(-/-)] mice. OHL was readily detected in lung homogenates from [Cftr.sup.(-/-)] mice infected with K56-2 but was only detected at levels slightly above background in a few mice infected with K56-12. Lung homogenates from mice infected with K56-2 had significantly higher levels of the inflammatory mediators murine macrophage inflammatory protein-2, KC/N51, interleukin-1 [beta] and interleukin-6 than those from K56-12-infected animals. These studies indicate that a functional CepIR quorum-sensing system contributes to the severity of B. cenocepacia infections. A zinc metalloprotease gene (zmpA) was shown to be regulated by CepR and may be one of the factors that accounts for the difference in virulence between the cepl mutant and the parent strain.

Bacteria degrading the quorum-sensing (QS) signal molecule N-hexanoylhomoserine lactone were isolated from a tobacco rhizosphere. Twenty-five isolates degrading this homoserine lactone fell into six groups according to their genomic REP-PCR and rrs PCR-RFLP profiles. Representative strains from each group were identified as members of the genera Pseudomonas, Comamonas, Variovorax and Rhodococcus. All these isolates degraded N-acylhomoserine lactones other than the hexanoic acid derivative, albeit with different specificity and kinetics. One of these isolates, Rhodococcus erythropolis strain W2, was used to quench QS-regulated functions of other microbes. In vitro, W2 strongly interfered with violacein production by Chromobacterium violaceum, and transfer of pathogenicity in Agrobacterium tumefaciens. In planta, R. erythropolis W2 markedly reduced the pathogenicity of Pectobacterium carotovorum subsp, carotovorum in potato tubers. These series of results reveal the diversity of the QS-interfering bacteria in the rhizosphere and demonstrate the validity of targeting QS signal molecules to control pathogens with natural bacterial isolates.

Quorum sensing systems serve as a means of 'census taking' of conspecific and non-conspecific bacteria in the near vicinity. The acylated homoserine lactone (AHL) quorum sensing system has been proposed to be primarily an intra-specific communication system, while the AI-2 autoinducer signalling system is proposed to be an interspecific communication system. Here it is shown that AI-2-like signalling in two marine Vibrio species, Vibrio vulnificus and 'Vibrio angustum' S14, induces the core response phenotypes of starvation adaptation and stress resistance, and that a signal antagonist can competitively inhibit these phenotypes. Furthermore, the signals produced by a range of Vibrio species have the ability to induce these phenotypes in V. vulnificus and 'V. angustum' S14, indicating that, at least in Vibrio species, AI-2-1ike signalling systems function as interspecies communication systems capable of 'cross-talk' and of regulating environmentally relevant phenotypes.

Research has been conducted on the Vibrio fischeri LuxR protein overproduced in Escherichia coli. The interactions between the tritiated halogenated furanone and LuxR protein have been investigated and the results indicate that LuxR concentration reduction is the mechanism used by furanones to control N-acyl-L-homoserine lactone-dependent phenotype expression.

Research has been conducted on the Pseudomonas aeruginosa and Burkholderia cepacia which form mixed biofilms in the lungs of the cystic fibrosis patients. The ability of these bacteria to communicate with each other via the N-acylhomoserine-lactone signal molecules has been investigated and the results indicate that in mixed biofilms intergeneric signalling occurs in one direction, from P. aeruginosa to B. cepacia.

Pseudomonas aeruginosa mutations in rhll and lasl quorum sensing systems bring milder chronic lung infection. In vivo pathogenic effects of the wild-type P. aeruginosa PAO1 and its double mutation, PAO1 lasl rhll, in which the signal-generating parts of the quorum sensing systems are defective, have been compared. The goal was to find out about importance of quorum sensing in chronic P. aeruginosa lung infection.

N-acylhomoserine lactones (AHL) have been detected in Pseudomonas aeruginosa-infected lungs of mice. This shows production and excretion of AHL molecules in vivo by the infecting organism. The view that expression of AHL molecules by P. aeruginosa during infection coincides with its pathogenesis has been supported. Green fluorescent protein (GFP)-expressing E. coli bacteria could be detected in the lung tissues after mice were challenged intratracheally with alginate beads having P. aeruginosa and E. coli and then killed on different days Pathogensis of P. aeruginosa is seen with expression of virulence factors, many controlled by two AHL-based quorum-sensing systems.

The biocontrol strain Pseudomonas fluorescens F113 has been found to produce the Rhizobium small bacteriocin, N-(3-hydroxy-7-cis-tetradecenoyl)homoserine lactone. It does so via HdtS, a putative novel N-acylhomoserine lactone synthase. Hdts is not in either of the known AHL synthase families and may be a member of a third protein family able to biosynthesize acylhomoserine lactones (AHLs). P. fluorescence F113 was cross-streaked against AHL biosensors able to detect short or long acyl chain AHLs. N-acylhomoserine lactones are quorum-sensing signal molecules and part of cell-density-dependent control of secondary metabolite and virulence gene expression. A gene, hdtS, was cloned and sequenced.

This paper describes isolation and characterization of oocydin A. The compound from Serratia marcescens is a 470 dalton in molecular mass with one chlorine atom, a carboxyl group and a tetrahydrofuran ring.

Saccharomyces cerevisiae was grown on glucono-delta-lactone and the induction of specific enzymes was investigated. Glucono-delta-lactone induced the synthesis of 6-phosphogluconate dehydrogenase (GND), 6-phosphogluconolactonase and gluconokinase, but affected the induction of all three enzymes in the gnd1 mutant. Revertants of the gnd1 mutant showed the importance of this catabolic pathway.

Research has been conducted on Pseudomonas aeruginosa proteins. The authors report that the purification of these proteins as hexahistidine fusion proteins has led to development of protein-acyl-homoserine lactone synthesis system.