Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Homoserine”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources
PubMed1990

Immunological characterization of in vitro forms of homoserine dehydrogenase from carrot suspension cultures.

Multiple forms of homoserine dehydrogenase (HSDH) from carrot (Daucus carota L.) have been identified. One form of HSDH (T-form) has a relative molecular weight of 240,000 and is strongly inhibited by threonine. Another form (K-form) has a relative molecular weight of 180,000 and is insensitive to inhibition by threonine. The interconversion of these two forms is dependent upon the presence or absence of threonine and potassium. Polyacrylamide electrophoretic gels stained for HSDH activity and protein, paralleled with Western blot analysis, verified the interconversion of the T- and K-forms in 5 millimolar threonine and 100 millimolar potassium, respectively. Carrot HSDH also aggregates to form higher molecular weight complexes of 240,000 up to 720,000 M(r.) Polyclonal antibody from mouse was raised against the T-form (240,000 M(r)) of carrot HSDH. Specificity of the mouse antisera to carrot HSDH was verified by immunoprecipitation and Western blot analysis. The T-form, K-form, and all of the higher molecular aggregates of carrot HSDH cross-reacted with the anti-HSDH antiserum. The antiserum also cross-reacted with soybean HSDH, but did not cross-react with either of the two HSDH forms found in Escherichia coli. A model for the in vivo regulation of threonine biosynthesis in the chloroplast is presented. The model is based on the interconversion of the HSDH forms by potassium and threonine.

Journal Article↗
PubMed2006

Induction of systemic resistance in tomato by N-acyl-L-homoserine lactone-producing rhizosphere bacteria.

N-acyl-L-homoserine lactone (AHL) signal molecules are utilized by Gram-negative bacteria to monitor their population density (quorum sensing) and to regulate gene expression in a density-dependent manner. We show that Serratia liquefaciens MG1 and Pseudomonas putida IsoF colonize tomato roots, produce AHL in the rhizosphere and increase systemic resistance of tomato plants against the fungal leaf pathogen, Alternaria alternata. The AHL-negative mutant S. liquefaciens MG44 was less effective in reducing symptoms and A. alternata growth as compared to the wild type. Salicylic acid (SA) levels were increased in leaves when AHL-producing bacteria colonized the rhizosphere. No effects were observed when isogenic AHL-negative mutant derivatives were used in these experiments. Furthermore, macroarray and Northern blot analysis revealed that AHL molecules systemically induce SA- and ethylene-dependent defence genes (i.e. PR1a, 26 kDa acidic and 30 kDa basic chitinase). Together, these data support the view that AHL molecules play a role in the biocontrol activity of rhizobacteria through the induction of systemic resistance to pathogens.

4-Butyrolactone↗
PubMed2004

N-acyl-l-homoserine lactones (AHLs) affect microbial community composition and function in activated sludge.

The role of intercellular signalling in the regulation of genes and phenotypes in a broad range of bacterial species is now firmly established. In contrast, the impact of intercellular signalling on microbial community parameters, such as species diversity and function, is less well understood. In this study the role of N-acyl-l-homoserine lactones (AHLs) in microbial community dynamics in an industrial wastewater treatment system is addressed. Seven proteobacterial strains producing compounds with AHL-like activity were isolated from the treatment plant. Three of these belong to genera with no previously identified AHL producing species. Addition of AHLs at 2 micro M to sludge samples generated changes in both community function (phenol degradation) and composition as determined by length heterogeneity PCR and denaturing gradient gel electrophoresis. Phenol degradation was more stable as a result of the AHL augmentation. A dominant functional member of the Thauera genus was transiently supplanted by a member of the Comomonas genus in response to AHL addition. This suggests that AHLs can play a role in mediating microbial community parameters and has implications for ecosystem function and industrial wastewater treatment.

4-Butyrolactone↗
PubMed2005

Diversity of N-acyl homoserine lactone-producing and -degrading bacteria in soil and tobacco rhizosphere.

In Gram-negative bacteria, quorum-sensing (QS) communication is mostly mediated by N-acyl homoserine lactones (N-AHSL). The diversity of bacterial populations that produce or inactivate the N-AHSL signal in soil and tobacco rhizosphere was investigated by restriction fragment length polymorphism (RFLP) analysis of amplified 16S DNA and DNA sequencing. Such analysis indicated the occurrence of N-AHSL-producing strains among the alpha-, beta- and gamma-proteobacteria, including genera known to produce N-AHSL (Rhizobium, Sinorhizobium and Pseudomonas) and novel genera with no previously identified N-AHSL-producing isolates (Variovorax, Sphingomonas and Massilia). The diversity of N-AHSL signals was also investigated in relation to the genetic diversity of the isolates. However, N-AHSL-degrading strains isolated from soil samples belonged to the Bacillus genus, while strains isolated from tobacco rhizospheres belonged to both the Bacillus genus and to the alpha subgroup of proteobacteria, suggesting that diversity of N-AHSL-degrading strains may be modulated by the presence of the tobacco plant. Among these rhizospheric isolates, novel N-AHSL-degrading genera have been identified (Sphingomonas and Bosea). As the first simultaneous analysis of both N-AHSL-degrading and -producing bacterial communities in a complex environment, this study revealed the coexistence of bacterial isolates, belonging to the same genus or species that may produce or degrade N-AHSL.

4-Butyrolactone↗
PubMed1996

Induction of phenazine biosynthesis in cultures of Pseudomonas aeruginosa by L-N-(3-oxohexanoyl)homoserine lactone.

A range of Pseudomonas spp. and other Gram-negative bacteria were screened for induction of antimicrobial activity in response to the autoregulatory factor L-N-(3-oxohexanoyl)homoserine lactone. In one of these, P. aeruginosa ATCC 10145, the production of phenazine metabolites was shown to be inducible in a dose-dependent manner. The production of phenazine-1-carboxamide increased over 50-fold compared to control cultures when supplemented with 200 micrograms/ml of the autoregulator. In addition, the production of an unidentified polar antibacterial substance by this strain increased with autoregulator concentration.

4-Butyrolactone↗
PubMed1998

Construction and analysis of luxCDABE-based plasmid sensors for investigating N-acyl homoserine lactone-mediated quorum sensing.

Plasmid reporter vectors have been constructed which respond to activation of LuxR and its homologues LasR and RhlR (VsmR) by N-acyl homoserine lactones (AHLs). The expression of luxCDABE from transcriptional fusions to PluxI, PlasI and PrhlI respectively, occurs in the presence of activating AHLs. A profile of structure/activity relationships is seen where the natural ligand is most potent. The characterisation of individual LuxR homologue/AHL combinations allows a comprehensive evaluation of quorum sensing signals from a test organism.

4-Butyrolactone↗
PubMed2000

Production of N-acyl-L-homoserine lactones by P. aeruginosa isolates from chronic lung infections associated with cystic fibrosis.

The N-acyl-L-homoserine lactones (AHLs) produced by sequential Pseudomonas aeruginosa isolates from chronically infected patients with cystic fibrosis were analyzed by thin-layer chromatography. It is demonstrated that both the amounts and the types of molecules synthesized by isolates from patients who were monitored over periods of up to 11 years do not change significantly during chronic colonization. However, in the case of a patient who became co-infected with an AHL-producing Burkholderia cepacia strain a dramatic reduction in the amounts of AHLs produced by the co-residing P. aeruginosa isolates was observed.

4-Butyrolactone↗
PubMed2007

Detection of quorum-sensing N-acyl homoserine lactone signal molecules by bacterial biosensors.

Many Gram-negative bacteria use N-acyl homoserine lactones (AHLs) as quorum-sensing (QS) signal molecules. AHL QS has been the subject of extensive investigation in the last decade and has become a paradigm for bacterial intercellular signaling. Research in AHL QS has been considerably aided by simple methods devised to detect AHLs using bacterial biosensors that phenotypically respond when exposed to exogenous AHLs. This article reviews and discusses the currently available bacterial biosensors which can be used in detecting and studying the different AHLs.

4-Butyrolactone↗
PubMed2006

Disruption of N-acyl homoserine lactone-mediated cell signaling and iron acquisition in epiphytic bacteria by leaf surface compounds.

Since N-acyl homoserine lactones (AHLs) are key mediators of cell density-dependent regulation of traits involved in virulence and epiphytic fitness in gram-negative bacteria such as Pseudomonas syringae, a variety of plant species were examined to determine their production of leaf surface compounds that could interact with these signaling systems. Leaf washings of 17 of 52 plant species tested stimulated or inhibited AHL-dependent traits in at least one of the bacterial reporter strains used. The active compounds from most plants could be distinguished from known AHLs due to different patterns of mobility during C8 and C18 reverse-phase thin-layer chromatography (TLC) and normal-phase TLC compared to the patterns for authentic bacterial AHLs. All plant extracts were also tested to determine their abilities to sequester iron and trigger bacterial siderophore synthesis on a medium containing abundant iron. Leaf washings from 16 of the 52 plant species, as well as tannic acid solutions, stimulated pyoverdine synthesis in P. syringae in a high-iron medium. These preparations also inhibited the growth of a P. syringae mutant unable to produce pyoverdine siderophores but not the growth of the wild-type bacterium. The stimulation of siderophore production and the growth inhibition by plant extracts and purified tannins were both reversed by addition of ferric chloride to culture media, indicating that iron was made unavailable by the compounds released onto the leaf surface.

4-Butyrolactone↗
PubMed2006

Synthesis of N-acyl homoserine lactone analogues reveals strong activators of SdiA, the Salmonella enterica serovar Typhimurium LuxR homologue.

N-Acyl homoserine lactones (AHLs) are molecules that are synthesized and detected by many gram-negative bacteria to monitor the population density, a phenomenon known as quorum sensing. Salmonella enterica serovar Typhimurium is an exceptional species since it does not synthesize its own AHLs, while it does encode a LuxR homologue, SdiA, which enables this bacterium to detect AHLs that are produced by other species. To obtain more information about the specificity of the ligand binding by SdiA, we synthesized and screened a limited library of AHL analogues. We identified two classes of analogues that are strong activators of SdiA: the N-(3-oxo-acyl)-homocysteine thiolactones (3O-AHTLs) and the N-(3-oxo-acyl)-trans-2-aminocyclohexanols. To our knowledge, this is the first report of compounds (the 3O-AHTLs) that are able to activate a LuxR homologue at concentrations that are lower than the concentrations of the most active AHLs. SdiA responds with greatest sensitivity to AHTLs that have a keto modification at the third carbon atom and an acyl chain that is seven or eight carbon atoms long. The N-(3-oxo-acyl)-trans-2-aminocyclohexanols were found to be less sensitive to deactivation by lactonase and alkaline pH than the 3O-AHTLs and the AHLs are. We also examined the activity of our library with LuxR of Vibrio fischeri and identified three new inhibitors of LuxR. Finally, we performed preliminary binding experiments which suggested that SdiA binds its activators reversibly. These results increase our understanding of the specificity of the SdiA-ligand interaction, which could have uses in the development of anti-quorum-sensing-based antimicrobials.

4-Butyrolactone↗
PubMed1995

Inactivation of rsmA leads to overproduction of extracellular pectinases, cellulases, and proteases in Erwinia carotovora subsp. carotovora in the absence of the starvation/cell density-sensing signal, N-(3-oxohexanoyl)-L-homoserine lactone.

The soft-rotting bacterium, Erwinia carotovora subsp. carotovora 71, produces extracellular enzymes such as pectate lyase isozymes (Pels), cellulase (Cel), polygalacturonase (Peh), and protease (Prt). While the extracellular levels of these enzymes are extremely low when the bacterium is grown in salts-yeast extract-glycerol (SYG) medium, the enzymatic activities are highly induced in SYG medium supplemented with celery extract. By transposon (mini-Tn5) mutagenesis, we isolated a RsmA- mutant, AC5070, which overproduces extracellular enzymes; the basal levels of Pel, Peh, and Cel in AC5070 are higher than the induced levels in the RsmA+ parent, AC5047. While Peh production is mostly constitutive in AC5070, Pel, Cel, and Prt production is still inducible with celery extract. The high basal levels of pel-1, pel-3, and peh-1 mRNAs in AC5070 demonstrate that overproduction of the pectolytic enzymes is due to the stimulation of transcription. Using chromosomal DNA flanking mini-Tn5 as a probe, we cloned the wild-type rsmA+ allele, which suppresses Pel, Peh, Cel, and Prt production in both RsmA+ and RsmA- strains. The RsmA- mutant, like its parent, produces N-(3-oxohexanoyl)-L-homoserine lactone (HSL), a starvation/cell density-sensing signal required for extracellular enzyme production. To examine the role of HSL, we constructed HSL-deficient strains by replacing hslI, a locus required for HSL production, with hslI::Tn3HoHo1-Spc. While the basal levels of Pel, Peh, Cel, and Prt are comparable in the RsmA- mutant and its HSL- derivative, these enzymes are barely detectable in the Hsl- derivative of the RsmA+ parent strain.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Butyrolactone↗
PubMed2002

Identification of quorum-quenching N-acyl homoserine lactonases from Bacillus species.

A range of gram-negative bacterial species use N-acyl homoserine lactone (AHL) molecules as quorum-sensing signals to regulate different biological functions, including production of virulence factors. AHL is also known as an autoinducer. An autoinducer inactivation gene, aiiA, coding for an AHL lactonase, was cloned from a bacterial isolate, Bacillus sp. strain 240B1. Here we report identification of more than 20 bacterial isolates capable of enzymatic inactivation of AHLs from different sources. Eight isolates showing strong AHL-inactivating enzyme activity were selected for a preliminary taxonomic analysis. Morphological phenotypes and 16S ribosomal DNA sequence analysis indicated that these isolates probably belong to the species Bacillus thuringiensis. Enzymatic analysis with known Bacillus strains confirmed that all of the strains of B. thuringiensis and the closely related species B. cereus and B. mycoides tested produced AHL-inactivating enzymes but B. fusiformis and B. sphaericus strains did not. Nine genes coding for AHL inactivation were cloned either by functional cloning or by a PCR procedure from selected bacterial isolates and strains. Sequence comparison of the gene products and motif analysis showed that the gene products belong to the same family of AHL lactonases.

4-Butyrolactone↗
PubMed2002

Genes encoding the N-acyl homoserine lactone-degrading enzyme are widespread in many subspecies of Bacillus thuringiensis.

Gram-negative bacteria can communicate with each other by N-acyl homoserine lactones (AHLs), which are quorum-sensing autoinducers. Recently, the aiiA gene (encoding an enzyme catalyzing the degradation of AHL) has been cloned from Bacillus sp. strain 240B1. During investigations in the course of the ongoing Bacillus thuringiensis subsp. morrisoni genome project, an aiiA homologue gene in the genome sequence was found. These results led to consideration of the possibility of the widespread existence of the gene in B. thuringiensis. aiiA homologue genes were found in 16 subspecies of B. thuringiensis, and their sequences were determined. Comparison of the Bacillus sp. strain 240B1 aiiA gene with the B. thuringiensis aiiA homologue genes showed high homologies of 89 to 95% and 90 to 96% in the nucleotide sequence and deduced amino acid sequence, respectively. Among the subspecies of B. thuringiensis having an aiiA gene, the subspecies aizawai, galleriae, kurstaki, kyushuensis, ostriniae, and subtoxicus were shown to degrade AHL. It was observed that recombinant Escherichia coli producing AiiA proteins also had AHL-degrading activity and could also attenuate the plant pathogenicity of Erwinia carotovora. These results indicate that insecticidal B. thuringiensis strains might have potential to compete with gram-negative bacteria in natural ecosystems by autoinducer-degrading activity.

4-Butyrolactone↗
PubMed2002

Possible quorum sensing in marine snow bacteria: production of acylated homoserine lactones by Roseobacter strains isolated from marine snow.

We report here, for the first time, that bacteria associated with marine snow produce communication signals involved in quorum sensing in gram-negative bacteria. Four of 43 marine microorganisms isolated from marine snow were found to produce acylated homoserine lactones (AHLs) in well diffusion and thin-layer chromatographic assays based on the Agrobacterium tumefaciens reporter system. Three of the AHL-producing strains were identified by 16S ribosomal DNA gene sequence analysis as Roseobacter spp., and this is the first report of AHL production by these alpha-PROTEOBACTERIA: It is likely that AHLs in Roseobacter species and other marine snow bacteria govern phenotypic traits (biofilm formation, exoenzyme production, and antibiotic production) which are required mainly when the population reaches high densities, e.g., in the marine snow community.

4-Butyrolactone↗
PubMed2003

The Ti plasmid of Agrobacterium tumefaciens harbors an attM-paralogous gene, aiiB, also encoding N-Acyl homoserine lactonase activity.

The Agrobacterium tumefaciens C58 genome contains three putative N-acyl homoserine lactone (acyl-HSL) hydrolases, which are closely related to the lactonase AiiA of Bacillus. When expressed in Escherichia coli, two of the putative acyl-HSL hydrolases, AttM and AiiB, conferred the ability to degrade acyl-HSLs on the host. In Erwinia strain 6276, the lactonases reduced the endogenous acyl-HSL level and the bacterial virulence in planta.

4-Butyrolactone↗
PubMed2004

Use of Sinorhizobium meliloti as an indicator for specific detection of long-chain N-acyl homoserine lactones.

Population-density-dependent gene expression in gram-negative bacteria involves the production of signal molecules characterized as N-acyl homoserine lactones (AHLs). The synthesis of AHLs by numerous microorganisms has been identified by using biosensor strains based on the Agrobacterium tumefaciens and Chromobacterium violaceum quorum-sensing systems. The symbiotic nitrogen-fixing bacterium Sinorhizobium meliloti is rapidly becoming a model organism for the study of quorum sensing. This organism harbors at least three different quorum-sensing systems (Sin, Mel, and Tra), which play a role in its symbiotic relationship with its host plant, alfalfa. The Sin system is distinguished among them for the production of long-chain AHLs, including C(18)-HL, the longest AHL reported so far. In this work, we show that construction of a sinI::lacZ transcriptional fusion results in a strain that detects long-chain AHLs with exquisite sensitivity. Overexpression of the SinR regulator protein from a vector promoter increases its sensitivity without loss of specificity. We also show that the resulting indicator strain can recognize long-chain AHLs produced by unrelated bacteria such as Paracoccus denitrificans and Rhodobacter capsulatus. This S. meliloti indicator strain should serve as a tool for the specific detection of long-chain AHLs in new systems.

4-Butyrolactone↗
PubMed2004

Regulation of the N-acyl homoserine lactone-dependent quorum-sensing system in rhizosphere Pseudomonas putida WCS358 and cross-talk with the stationary-phase RpoS sigma factor and the global regulator GacA.

Quorum sensing is a cell population-density dependent regulatory system which in gram-negative bacteria often involves the production and detection of N-acyl homoserine lactones (AHLs). Some Pseudomonas putida strains have been reported to produce AHLs, and one quorum-sensing locus has been identified. However, it appears that the majority of strains do not produce AHLs. In this study we report the identification and regulation of the AHL-dependent system of rhizosphere P. putida WCS358. This system is identical to the recently identified system of P. putida strain IsoF and very similar to the las system of Pseudomonas aeruginosa. It is composed of three genes, the luxI family member ppuI, the putative repressor rsaL, and the luxR family member ppuR. A genomic ppuR::Tn5 mutant of strain WCS358 was identified by its inability to produce AHLs when it was cross-streaked in close proximity to an AHL biosensor, whereas an rsaL::Tn5 genomic mutant was identified by its ability to overproduce AHL molecules. Using transcriptional promoter fusions, we studied expression profiles of the rsaL, ppuI, and ppuR promoters in various genetic backgrounds. At the onset of the stationary phase, the autoinducer synthase ppuI gene expression is under positive regulation by PpuR-AHL and under negative regulation by RsaL, indicating that the molecules could be in competition for binding at the ppuI promoter. In genomic rsaL::Tn5 mutants ppuI expression and production of AHL levels increased dramatically; however, both processes were still under growth phase regulation, indicating that RsaL is not involved in repressing AHL production at low cell densities. The roles of the global response regulator GacA and the stationary-phase sigma factor RpoS in the regulation of the AHL system at the onset of the stationary phase were also investigated. The P. putida WCS358 gacA gene was cloned and inactivated in the genome. It was determined that the three global regulatory systems are closely linked, with quorum sensing and RpoS regulating each other and GacA positively regulating ppuI expression. Studies of the regulation of AHL quorum-sensing systems have lagged behind other studies and are important for understanding how these systems are integrated into the overall growth phase and metabolic status of the cells.

Bacterial Proteins↗