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PubMed2005

Quorum sensing in halophilic bacteria: detection of N-acyl-homoserine lactones in the exopolysaccharide-producing species of Halomonas.

Some members of the moderately halophilic genus Halomonas, such as H. eurihalina, H. maura, H. ventosae and H. anticariensis, produce exopolysaccharides with applications in many industrial fields. We report here that these four species also produce autoinducer molecules that are involved in the cell-to-cell signaling process known as quorum sensing. By using the N-acyl homoserine lactone (AHL) indicator strains Agrobacterium tumefaciens NTL4 (pZRL4) and Chromobacterium violaceum CV026, we discovered that all the Halomonas strains examined synthesize detectable AHL signal molecules. The synthesis of these compounds was growth-phase dependent and maximal activity was reached during the late exponential to stationary phases. One of these AHLs seems to be synthesized only in the stationary phase. Some of the AHLs produced by H. anticariens FP35(T) were identified by gas chromatography/mass spectrometry and electrospray ionization tandem mass spectrometry as N-butanoyl homoserine lactone (C(4)-HL), N-hexanoyl homoserine lactone (C(6)-HL), N-octanoyl homoserine lactone (C(8)-HL) and N-dodecanoyl homoserine lactone (C(12)-HL). This study suggests that quorum sensing may also play an important role in extreme environments.

4-Butyrolactone↗
PubMed2000

Intracellular Ca(2+) mobilization and kinase activity during acylated homoserine lactone-dependent quorum sensing in Serratia liquefaciens.

Quorum sensing in Gram-negative bacteria involves acylated homoserine lactones (AHLs) and a transcription factor, activated by the AHLs. In this study, a possible involvement of intracellular Ca(2+) as second messenger and/or protein kinase activity during signal transduction is analyzed. When N-hexanoyl-l-homoserine lactone was added to a suspension of Fura-2-loaded Serratia liquefaciens, there was a decline in [Ca(2+)](i), measured as a decrease in the Fura-2 fluorescence ratio. As controls, the addition of the signal molecule N-3-oxohexanoyl-l-homoserine lactone, which is not produced by S. liquefaciens, did not induce changes in [Ca(2+)](i). Using a protein kinase activity assay on AHL-stimulated cells, an increase in kinase activity after N-butanoyl-l-homoserine lactone stimulation of S. liquefaciens cells was detected, whereas the kinase activity induced by N-3-oxohexanoyl-l-homoserine lactone was not statistically significant. The conclusion from this study is that changes in [Ca(2+)](i) are involved in quorum sensing signal transduction in the Gram-negative bacteria S. liquefaciens. We also conclude that kinase activity is induced in S. liquefaciens upon AHL stimulation. We suggest that the transient intracellular [Ca(2+)] changes and kinase activity, activated by the AHL signal, are critical for the quorum-sensing signal transduction.

4-Butyrolactone↗
PubMed2006

N-(3-oxo-acyl)homoserine lactones signal cell activation through a mechanism distinct from the canonical pathogen-associated molecular pattern recognition receptor pathways.

Innate immune system receptors function as sensors of infection and trigger the immune responses through ligand-specific signaling pathways. These ligands are pathogen-associated products, such as components of bacterial walls and viral nuclear acids. A common response to such ligands is the activation of mitogen-activated protein kinase p38, whereas double-stranded viral RNA additionally induces the phosphorylation of eukaryotic translation initiation factor 2alpha (eIF2alpha). Here we have shown that p38 and eIF2alpha phosphorylation represent two biochemical markers of the effects induced by N-(3-oxo-acyl)homoserine lactones, the secreted products of a number of Gram-negative bacteria, including the human opportunistic pathogen Pseudomonas aeruginosa. Furthermore, N-(3-oxo-dodecanoyl)homoserine lactone induced distension of mitochondria and the endoplasmic reticulum as well as c-jun gene transcription. These effects occurred in a wide variety of cell types including alveolar macrophages and bronchial epithelial cells, requiring the structural integrity of the lactone ring motif and its natural stereochemistry. These findings suggest that N-(3-oxo-acyl)homoserine lactones might be recognized by receptors of the innate immune system. However, we provide evidence that N-(3-oxo-dodecanoyl)homoserine lactone-mediated signaling does not require the presence of the canonical innate immune system receptors, Toll-like receptors, or two members of the NLR/Nod/Caterpillar family, Nod1 and Nod2. These data offer a new understanding of the effects of N-(3-oxo-dodecanoyl)homoserine lactone on host cells and its role in persistent airway infections caused by P. aeruginosa.

4-Butyrolactone↗
PubMed1990

Yeast homoserine kinase. Characteristics of the corresponding gene, THR1, and the purified enzyme, and evolutionary relationships with other enzymes of threonine metabolism.

THR1, the gene from Saccharomyces cerevisiae, encoding homoserine kinase, one of the threonine biosynthetic enzymes, has been cloned by complementation. The nucleotide sequence of a 3.1-kb region carrying this gene reveals an open reading frame of 356 codons, corresponding to about 40 kDa for the encoded protein. The presence of three canonical GCN4 regulatory sequences in the upstream flanking region suggests that the expression of THR1 is under the general amino acid control. In parallel, the enzyme was purified by four consecutive column chromatographies, monitoring homoserine kinase activity. In SDS gel electrophoresis, homoserine kinase migrates like a 40-kDa protein; the native enzyme appears to be a homodimer. The sequence of the first 15 NH2-terminal amino acids, as determined by automated Edman degradation, is in accordance with the amino acid sequence deduced from the nucleotide sequence. Computer-assisted comparison of the yeast enzyme with the corresponding activities from bacterial sources showed that several segments among these proteins are highly conserved. Furthermore, the observed homology patterns suggest that the ancestral sequences might have been composed from separate (functional) domains. A block of very similar amino acids is found in the homoserine kinases towards the carboxy terminus that is also present in many other proteins involved in threonine (or serine) metabolism; this motif, therefore, may represent the binding site for the hydroxyamino acids. Limited similarity was detected between a motif conserved among the homoserine kinases and consensus sequences found in other mono- or dinucleotide-binding proteins.

Amino Acid Sequence↗
PubMed2001

Multiple N-acyl homoserine lactone signals of Rhizobium leguminosarum are synthesized in a distinct temporal pattern.

A common form of bacterial quorum sensing involves the production and release of acyl homoserine lactone (AHL) signal metabolites. The nitrogen-fixing symbiont Rhizobium leguminosarum reportedly produces at least six different AHLs, but little is known about the regulation of biosynthesis of these molecules. We used a radiolabeling protocol to quantify the relative amounts of AHLs synthesized over time by R. leguminosarum cells with and without the symbiosis plasmid pRL1JI. Cells containing pRL1JI were found to produce three predominant signals. In decreasing order of abundance, these were N-(3-oxo)octanoyl homoserine lactone [(3-O)C(8)HSL], N-octanoyl homoserine lactone, and N-hexanoyl homoserine lactone. Cells without pRL1JI produced only two major signals, N-(3-hydroxy-7-cis)tetradecanoyl homoserine lactone [(3-OH)C(14:1)HSL] and (3-O)C(8)HSL. Each AHL exhibited a distinct temporal pattern of synthesis, suggesting that each AHL is subject to unique regulatory mechanisms. While (3-O)C(8)HSL was produced in both cultures, the patterns of synthesis were different in cells with and without pRL1JI, possibly as a result of redundant gene functions that are present on both the chromosome and the symbiosis plasmid. None of the AHLs appeared to regulate its own biosynthesis, although exogenous (3-OH)C(14:1)HSL did activate synthesis of the three AHLs made by cells containing pRL1JI. These results indicate that the synthesis of multiple AHLs in R. leguminosarum is regulated by complex mechanisms that operate independently of quorum sensing itself but that (3-OH)C(14:1)HSL can supersede these controls in pRL1JI-containing cells. This work provides an important global perspective for AHL regulation that both complements and contrasts with the results of previous studies performed with isolated gene systems.

4-Butyrolactone↗
PubMedDate not supplied

Biologically active ether lipids: incorporation of long-chain precursors into 1(3),2-diacylglycero-3(1)-O-4'-(N,N,N-trimethyl)homoserines and other lipids of Chlorella fusca.

The lipids of Chlorella fusca are composed of the ester lipids typical of photosynthetically active cells. In addition, there occurs a class of less common ether lipids, the biologically active 1(3),2-diacylglycero-3(1)-O-4'-(N,N,N- trimethyl)homoserines, at a level of about 1.3% of total lipids. The acyl moieties of the total lipids include saturated as well as mono-, di- and tri-unsaturated species with chain lengths of 16 and 18 carbon atoms, the major constituents being palmitic and oleic acids. In both the diacylglycerophosphocholines, i.e., the major class of ester phospholipids, and the diacylglycero-4'-O-(N,N,N-trimethyl)homoserines palmitic acid is located predominantly at position 1 of the glycerol backbone, whereas oleic acid is almost equally distributed between positions 1 and 2; palmitoleic and polyunsaturated fatty acids are esterified preferentially at position 2. Incubation of C. fusca cultures with 14C-labeled fatty acids leads to their rapid incorporation into various lipid classes. Oleic and palmitic acids are incorporated at a faster rate than stearic acid (18:1 greater than 16:0 much greater than 18:0). 1,2- and 1,3-Diacylglycerols are the most prominent intermediates of early metabolism of the exogenous fatty acids. In the course of time, a steady decrease of radioactive 1,2-diacylglycerols is observed that is accompanied by an increase in labeled triacylglycerols, diacylglycerophosphocholines, and diacylglycero-O-(N,N,N-trimethyl)homoserines. The stereospecific distribution of acyl moieties in the diacylglycero-O-(N,N,N-trimethyl)homoserines in C. fusca indicates that these ether lipids are derived from 1,2-diacylglycerol intermediates. This notion is supported by the finding that during incubation with radioactively labeled fatty acids the formation of diacylglycero-O-(N,N,N-trimethyl)homoserines parallels the biosynthesis of both diacylglycerophosphocholines and diacylglycerophosphoethanolamines, two classes of phospholipids which are known to be derived from 1,2-diacylglycerols. The mechanism of the formation of the ether bond, however, is as yet unknown. Incubation of C. fusca cultures with 14C-labeled fatty acids or alcohols leads to the formation of fair proportions of wax esters that are labeled in both the acyl and the alkyl moieties, indicating that in these algae fatty acids and alcohols are interconverted. 14C-Labeled long-chain alcohols are not incorporated into the alkyl moieties of ether lipids, whereas labeled 1-O-alkylglycerols are used, though to a very small extent, as precursors of ether phospholipids.

Chlorella↗
PubMed1990

The mechanism of antifungal action of (S)-2-amino-4-oxo-5-hydroxypentanoic acid, RI-331: the inhibition of homoserine dehydrogenase in Saccharomyces cerevisiae.

We have explored the mechanism by which an antifungal antibiotic, (S)-2-amino-4-oxo-5-hydroxypentanoic acid, RI-331, preferentially inhibits protein biosynthesis in Saccharomyces cerevisiae, by inhibiting the biosynthesis of the aspartate family of amino acids, methionine, isoleucine and threonine. This inhibition was effected by inhibiting the biosynthesis of their common intermediate precursor homoserine. The target enzyme of RI-331 was homoserine dehydrogenase (EC.1.1.1.3) which is involved in converting aspartate semialdehyde to homoserine in the pathway from aspartate to homoserine. The enzyme is lacking in animals. So the antibiotic is selectively toxic to prototrophic fungi.

Alcohol Oxidoreductases↗
PubMed1976

The threonine-sensitive homoserine dehydrogenase and aspartokinase activities of Escherichia coli K-12. Incubation of the enzyme in alkaline conditions: dissociation and disulfide-bridge formation.

Aspartokinase I - homoserine dehydrogenase I from Escherichia coli K-12, a homotetrameric enzyme, dissociates into dimers upon alkaline treatment. Both aspartokinase and homoserine dehydrogenase inactivation, as well as desensitazion towards L-threonine, occur in a multi-step process. Dithiothreitol stabilizes a dimeric form retaining full activity and sensitivity; L-homoserine stabilizing another dimeric form devoid of aspartokinase activity and retaining a substantial dehydrogenase activity insensitive toward L-threonine. A model is proposed showing that dissociation into dimers occurs in a first step, the resulting dimer losing both aspartokinase and homoserine dehydrogenase sensitivity in two subsequent steps involving the formation of intrachain disulfide bonds.

Alcohol Oxidoreductases↗
PubMed1993

Threonine synthase of Escherichia coli: inhibition by classical and slow-binding analogues of homoserine phosphate.

L-threo-3-Hydroxyhomoserine phosphate, derived from the antimetabolites L-threo-3-hydroxyaspartate and L-threo-3-hydroxyhomoserine [Shames, S. L., Ash, D. E., Wedler, F. C., and Villafranca, J. J. (1984) J. Biol. Chem. 258, 15331-15339], is a classical competitive inhibitor of threonine synthase (Ki = 6 microM) with structural elements of both substrate and product. L-2-Amino-5-phosphonovaleric acid also inhibits the enzyme competitively with a Ki (31 microM), comparable to Km for L-homoserine phosphate. In contrast, a structural analogue of Hse-P, L-2-amino-3-[(phosphonomethyl)thio]propionic acid exhibits a Ki = 0.11 microM (ca. 100-fold less than Km for L-Hse-P), along with "slow, tight" inhibition kinetics. Nuclear magnetic resonance was used with these inhibitors to probe for pyridoxal phosphate-catalyzed hydrogen-deuterium exchange reactions characteristic of substrates. With L-threo-3-hydroxy-homoserine phosphate, H-D exchange occurs only at the C-alpha position, but for homoserine in the presence of phosphate and for L-2-amino-5-phosphonovaleric acid and L-amino-3[(phosphonomethyl)thio]propionic acid (APMTP), H-D exchange occurs at C-alpha and stereospecifically at C-beta. For L-homoserine plus phosphate and L-2-amino-5-phosphonovaleric acid, the rate of H-D exchange at C-alpha is 8-45 times faster than at C-beta. For L-2-amino-3-[(phosphonomethyl)thio]propionic acid, the C-alpha to C-beta exchange rate ratio is near unity, due to a 700-fold decrease in the C-alpha rate for the analogue. Taken with information from molecular modeling, these data can be interpreted in terms of the current working hypothesis for the catalytic mechanism. Specifically, the slow, tight inhibition by APMTP results from its being carried further into the catalytic cycle than other analogues prior to forming an intermediate that is blocked from further catalysis.

2-Amino-5-phosphonovalerate↗
PubMed1983

Aspartate kinase and homoserine dehydrogenase of Candida utilis.

Aspartate kinase and homoserine dehydrogenase activity were assayed in a dialyzed cell-free extract of Candida utilis. Aspartate kinase was partly inhibited by ATP-Mg and by Mg2+ alone. There appear to be two isoenzymes of aspartate kinase in the yeast, one heat-labile, the other relatively heat-stable. The first is subject to feedback inhibition by threonine, the other is threonine-resistant. Neither aspartate kinase nor homoserine dehydrogenase is the rate-limiting enzyme in methionine biosynthesis. Homoserine dehydrogenase measured in the forward direction showed an activity five times higher than aspartate kinase. No regulatory interaction could be demonstrated for this enzyme. No repression of aspartate kinase and homoserine dehydrogenase synthesis by threonine, methionine or both amino acids was observed.

Adenosine Triphosphate↗
PubMed2001

The methionine biosynthetic pathway from homoserine in Pseudomonas putida involves the metW, metX, metZ, metH and metE gene products.

Biosynthesis of methionine from homoserine in Pseudomonas putida takes place in three steps. The first step is the acylation of homoserine to yield an acyl-L-homoserine. This reaction is catalyzed by the products of the metXW genes and is equivalent to the first step in enterobacteria, gram-positive bacteria and fungi, except that in these microorganisms the reaction is catalyzed by a single polypeptide (the product of the metA gene in Escherichia coli and the met5 gene product in Neurospora crassa). In Pseudomonas putida, as in gram-positive bacteria and certain fungi, the second and third steps are a direct sulfhydrylation that converts the O-acyl-L-homoserine into homocysteine and further methylation to yield methionine. The latter reaction can be mediated by either of the two methionine synthetases present in the cells.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed2004

New phenolic inhibitors of yeast homoserine dehydrogenase.

A relatively unexploited potential target for antimicrobial agents is the biosynthesis of essential amino acids. Homoserine dehydrogenase, which reduces aspartate semi-aldehyde to homoserine in a NAD(P)H-dependent reaction, is one such target that is required for the biosynthesis of Met, Thr, and Ile from Asp. We report a small molecule screen of yeast homoserine dehydrogenase that has identified a new class of phenolic inhibitors of this class of enzyme. X-ray crystal structural analysis of one of the inhibitors in complex with homoserine dehydrogenase reveals that these molecules bind in the amino acid binding region of the active site and that the phenolic hydroxyl group interacts specifically with the backbone amide of Gly175. These results provide the first nonamino acid inhibitors of this class of enzyme and have the potential to be exploited as leads in antifungal compound design.

Antifungal Agents↗
PubMed2003

Identification and characterization of the new gene rhtA involved in threonine and homoserine efflux in Escherichia coli.

The rhtA gene known as the ybiF ORF in the genome of Escherichia coli was identified as a new gene involved in threonine and homoserine efflux. This gene encodes a highly hydrophobic membrane protein that contains 10 predicted transmembrane segments. The rhtA23 mutation, which is an A-for-G substitution at position -1 in relation to the ATG start codon, increases the expression level of the rhtA gene. The overexpression of rhtA gene results in resistance to inhibitory concentrations of homoserine, threonine and a variety of other amino acids and amino acid analogues, reduced threonine and homoserine accumulation in resistant cells and increased production of threonine, homoserine, lysine and proline by the respective producing strains. The RhtA protein belongs to a vast family of transporters. The genome of E. coli contains at least 10 paralogues of RhtA. Phylogenetic analysis indicates that a common ancestor of living organisms contained several RhtA homologues.

Amino Acid Sequence↗
PubMed1978

Detection of the homology among proteins by immunochemical cross-reactivity between denatured antigens. Application to the threonine and methionine regulated aspartokinases-homoserine dehydrogenases from Escherichia coli K 12.

The two isofunctional enzymes aspartokinases-homoserine dehydrogenases I and II from Escherichia coli K 12 are compared using immunochemical techniques. The antibodies raised against one of these two proteins when in its native state can only recognize the homologous antigen, whether it is native or denatured. Contrarily, the antibodies raised against one of these two proteins when in its denatured state can recognize both the homologous and heterologous denatured antigens. The existence of this cross-reaction only between the two denatured aspartokinases-homoserine dehydrogenases suggests that these two enzymes have some similarity since such a reaction is not detected with several other denatured proteins. The regions involved in this similarity are buried inside the native proteins, and become exposed only upon denaturation. The same results, the existence of a cross-reaction between denatured species and none between the native ones, is obtained with proteolytic fragments derived from these two proteins and endowed with homoserine dehydrogenase activity. This resemblance between the two aspartokinases-homoserine dehydrogenases suggests that these proteins derive from a common ancestor. It is also proposed that such a cross-reaction between two denatured proteins is evidence for an homology between their amino acid sequences, and that the use of denatured proteins as both immunogens and antigens could be useful in detecting sequence homologies.

Alkylation↗
PubMed1993

Agrobacterium conjugation and gene regulation by N-acyl-L-homoserine lactones.

Conjugal opines secreted by crown gall tumours induce strains of Agrobacterium tumefaciens that are donors of Ti plasmids to produce a diffusible conjugation factor. This enhances the conjugal transfer efficiency of the Ti plasmid in other strains of A. tumefaciens. This factor behaves as a secondary messenger, transmitting the environmental information to tra genes. Here we report the use of spectrometry to show that this factor is identical to synthetic N-(beta-oxo-octan-1-oyl)-L-homoserine lactone and confirm that the synthetic compound is biologically active. N-(Hexan-1-oyl)-L-homoserine lactone has also been detected. A closely related molecule, N-(beta-oxo-hexan-1-oyl)-L-homoserine lactone, autoinduces bioluminescence in the distantly related bacterium, Vibrio fischeri. N-Acyl-homoserine lactones thus seem to be conserved molecules in which the length and nature of the lipophilic acyl chain determines the biological function to be regulated. Mutants that do not produce the factor fail to conjugate unless supplied with it in the induction medium (our unpublished data). These data indicate that the conjugation factor is an autoinducer and a key signal molecule in the conjugation system of A. tumefaciens. It is, to our knowledge, the first example of a second messenger molecule in a bacterial conjugation system.

Agrobacterium tumefaciens↗
PubMed1999

The Pseudomonas aeruginosa quorum-sensing signal molecule, N-(3-oxododecanoyl)-L-homoserine lactone, inhibits porcine arterial smooth muscle contraction.

The Pseudomonas aeruginosa quorum sensing molecule N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL) has been shown to suppress cytokine production in macrophages. We have examined the effect of OdDHL and related compounds on constrictor tone of porcine blood vessels. OdDHL (1-30 microM) caused a concentration-dependent inhibition of U46619-induced contractions of the coronary artery through a largely endothelium-independent mechanism, but was markedly less effective in the pulmonary artery. Quantitively similar effects to those produced by OdDHL were observed with N-(3-oxododecanoyl)-L-homocysteine thiolactone, a thiolactone derivative, while N-3-oxododecanamide, a lactone-free acyl analogue, possessed 1/3rd the potency as a vasorelaxant. Neither N-butanoyl-L-homoserine lactone nor L-homoserine lactone (up to 30 microM) were active. Our findings indicate that OdDHL inhibits vasoconstrictor tone of both pulmonary and coronary blood vessels from the pig. The vasorelaxant action of OdDHL appears to be primarily determined by the N-acyl chain length, with a minor contribution by the homoserine lactone moiety.

4-Butyrolactone↗
PubMed1998

Characterization of the Erwinia chrysanthemi expI-expR locus directing the synthesis of two N-acyl-homoserine lactone signal molecules.

The plant pathogen Erwinia chrysanthemi produces three acyl-homoserine lactones (acyl-HSLs). One has been identified as N-(3-oxohexanoyl)-homoserine lactone (OHHL), and the two others were supposed to be N (hexanoyl)-homoserine lactone (HHL) and N-(decanoyl)-homoserine lactone (DHL). The genes for a quorum-sensing signal generator (expI) and a response regulator (expR) were cloned. These genes are convergently transcribed and display high similarity to the expI-expR genes of Erwinia carotovora. ExpI is responsible for both OHHL and HHL production. Inactivation of expl had little effect on pectinase synthesis in E. chrysanthemi, as expression of only two of the pectate lyase genes, pelA and pelB, was decreased. E. chrysanthemi expR mutants still produced acyl-HSL and pectinases. However, gel shift and DNAse I footprinting experiments showed that the purified E. chrysanthemi ExpR protein binds specifically to the promoter regions of the five major pel genes. Addition of OHHL modified the ExpR-DNA bandshift profiles, indicating that ExpR interacts with OHHL and binds to DNA in different ways, depending on the OHHL concentration. Localization of the ExpR binding sites just upstream of promoter regions suggests that ExpR functions as an activator of pel expression in the presence of OHHL. The absence of a phenotype in expR mutants strongly suggests that at least an additional interchangeable ExpR homologue exists in E. chrysanthemi. Finally, transcription of expI::uidA and expR::uidA fusions is dependent on the population density, suggesting the existence of a quorum-sensing hierarchy in E. chrysanthemi. These results suggest that the expI-expR locus is part of a complex autoregulatory system that controls quorum sensing in E. chrysanthemi.

4-Butyrolactone↗
PubMed1995

Multiple N-acyl-L-homoserine lactone signal molecules regulate production of virulence determinants and secondary metabolites in Pseudomonas aeruginosa.

Pseudomonas aeruginosa produces a spectrum of exoproducts many of which have been implicated in the pathogenesis of human infection. Expression of some of these factors requires cell-cell communication involving the interaction of a small diffusible molecule, an "autoinducer," with a positive transcriptional activator. In P. aeruginosa PAO1, LasI directs the synthesis of the autoinducer N-(3-oxododecanoyl)-L-homoserine lactone (OdDHL), which activates the positive transcriptional activator, LasR. Recently, we have discovered a second signaling molecule-based modulon in PAO1, termed vsm, which contains the genes vsmR and vsmI. Using HPLC, mass spectrometry, and NMR spectroscopy we now establish that in Escherichia coli, VsmI directs the synthesis of N-butanoyl-L-homoserine lactone (BHL) and N-hexanoyl-L-homoserine lactone (HHL). These compounds are present in the spent culture supernatants of P. aeruginosa in a molar ratio of approximately 15:1 and their structures were unequivocally confirmed by chemical synthesis. Addition of either BHL or HHL to PAN067, a pleiotropic P. aeruginosa mutant unable to synthesize either of these autoinducers, restored elastase, chitinase, and cyanide production. In E. coli carrying a vsmR/vsmI'::lux transcriptional fusion, BHL and HHL activated VsmR to a similar extent. Analogues of these N-acyl-L-homoserine lactones in which the N-acyl side chain has been extended and/or oxidized at the C-3 position exhibit substantially lower activity (e.g., OdDHL) or no activity (e.g., dDHL) in this lux reporter assay. These data indicate that multiple families of quorum sensing modulons interactively regulate gene expression in P. aeruginosa.

Bacterial Proteins↗