Acylhomoserine Lactones (acylhomoserine + lactone)

Distribution by Scientific Domains
Distribution within Life Sciences

Selected Abstracts

A metagenomic analysis of soil bacteria extends the diversity of quorum-quenching lactonases

Kashif Riaz
Summary A metagenomic library of 10 121 clones, generated from bacteria inhabiting a pasture soil from France, was screened for the presence of fosmids conferring either N -acylhomoserine lactone (NAHL) synthesis or NAHL degradation ability upon their Escherichia coli host. No clone producing NAHLs was identified whereas one, containing a 31 972 bp insert in fosmid p2H8, allowed NAHL degradation. This led to the cloning and identification of a gene, qlcA, encoding an NAHL-lactonase activity, as judged by lactone-ring closure and HPLC/MS analyses of NAHL degradation products. The qlcA gene efficiently quenched quorum-sensing regulated pathogenic functions when expressed in Pectobacterium carotovorum. The QlcA peptide belongs to the family of zinc-dependent metallohydrolases and appears to be distantly related to other NAHL-lactonases discovered in Agrobacterium, Bacillus, Photorhabdus and Rhizobium. In-silico analysis of the metagenomic insert revealed the occurrence of 20 orf, with a constant GC% and codon usage, suggesting a unique bacterial origin. Nine out of these 20 orf were homologous to genes encoding biosynthesis of arginine; they were clustered with an unusual succession argFJADBCRGH. The fosmid p2H8 is able to complement the argA, argB and argC mutants in E. coli. Phylogenetic analysis showed that 9 orf out of 20 were related to sequences from members of the Acidobacteria, supporting the hypothesis that the analysed insert might be originated from an organism related to this phylum. [source]

Autoinducers extracted from microbial mats reveal a surprising diversity of N -acylhomoserine lactones (AHLs) and abundance changes that may relate to diel pH

Alan W. Decho
Summary Microbial mats are highly structured and diverse communities, and one of the earliest-known life assemblages. Mat bacteria interact within an environment marked by strong geochemical gradients and fluctuations. We examined natural mat systems for the presence of autoinducers involved in quorum sensing, a form of cell,cell communication. Our results revealed that a diverse array of N -acylhomoserine lactones (AHLs) including C4 - to C14 -AHLs, were identified from mat extracts using mass spectrometry (MS), with further confirmation by MS/MS-collision-induced dissociation (CID), and additions of external standards. Microelectrode measurements showed that mats exhibited diel pH fluctuations, ranging from alkaline (pH 9.4) during daytime (net photosynthesis) to acidic (pH 6.8) during darkness (net respiration/fermentation). Under laboratory conditions, AHLs having shorter acyl-chains were degraded within the time frame that daily alkaline pH (> 8.2) conditions exist in mats. Intensive sampling of mats after full day- or night-time incubations revealed that accumulations of extractable shorter-chain AHLs (e.g. C8 - and C10 -AHLs) were significantly (P < 0.001) diminished during daytime. Our study offers evidence that stabilities of AHLs under natural conditions may be influenced by the proximal extracellular environment. We further propose that the ancient periodicity of photosynthesis/respiration in mats may potentially drive a mechanism for diel differences in activities of certain autoinducers, and hence bacterial activities mediated through quorum sensing. [source]

Endophytic root colonization of gramineous plants by Herbaspirillum frisingense

Michael Rothballer
Abstract Herbaspirillum frisingense is a diazotrophic betaproteobacterium isolated from C4-energy plants, for example Miscanthus sinensis. To demonstrate endophytic colonization unequivocally, immunological labeling techniques using monospecific polyclonal antibodies against two H. frisingense strains and green fluorescent protein (GFP)-fluorescence tagging were applied. The polyclonal antibodies enabled specific in situ identification and very detailed localization of H. frisingense isolates Mb11 and GSF30T within roots of Miscanthus×giganteus seedlings. Three days after inoculation, cells were found inside root cortex cells and after 7 days they were colonizing the vascular tissue in the central cylinder. GFP-tagged H. frisingense strains could be detected and localized in uncut root material by confocal laser scanning microscopy and were found as endophytes in cortex cells, intercellular spaces and the central cylinder of barley roots. Concerning the production of potential plant effector molecules, H. frisingense strain GSF30T tested positive for the production of indole-3-acetic acid, while Mb11 was shown to produce N -acylhomoserine lactones, and both strains were able to utilize 1-aminocyclopropane-1-carboxylate (ACC), providing an indication of the activity of an ACC-deaminase. These results clearly present H. frisingense as a true plant endophyte and, although initial greenhouse experiments did not lead to clear plant growth stimulation, demonstrate the potential of this species for beneficial effects on the growth of crop plants. [source]

Indole and 7-hydroxyindole diminish Pseudomonas aeruginosa virulence

Jintae Lee
Summary Indole is an extracellular biofilm signal for Escherichia coli, and many bacterial oxygenases readily convert indole to various oxidized compounds including 7-hydroxyindole (7HI). Here we investigate the impact of indole and 7HI on Pseudomonas aeruginosa PAO1 virulence and quorum sensing (QS)-regulated phenotypes; this strain does not synthesize these compounds but degrades them rapidly. Indole and 7HI both altered extensively gene expression in a manner opposite that of acylhomoserine lactones; the most repressed genes encode the mexGHI-opmD multidrug efflux pump and genes involved in the synthesis of QS-regulated virulence factors including pyocyanin (phz operon), 2-heptyl-3-hydroxy-4(1H)-quinolone (PQS) signal (pqs operon), pyochelin (pch operon) and pyoverdine (pvd operon). Corroborating these microarray results, indole and 7HI decreased production of pyocyanin, rhamnolipid, PQS and pyoverdine and enhanced antibiotic resistance. In addition, indole affected the utilization of carbon, nitrogen and phosphorus, and 7HI abolished swarming motility. Furthermore, 7HI reduced pulmonary colonization of P. aeruginosa in guinea pigs and increased clearance in lungs. Hence, indole-related compounds have potential as a novel antivirulence approach for the recalcitrant pathogen P. aeruginosa. [source]

Integration of environmental and host-derived signals with quorum sensing during plant,microbe interactions

J. A. Newton
Summary Many plant-associated microbes use secreted autoinducer molecules, including N -acylhomoserine lactones (AHLs), to regulate diverse behaviours in association with their population density (quorum sensing). Often, these responses are affected by environmental conditions, including the presence of other AHL-producing bacterial species. In addition, plant-derived metabolites, including products that arise as a direct result of the bacterial infection, may profoundly influence AHL-regulated behaviours. These plant products can interact directly and indirectly with the quorum-sensing network and can profoundly affect the quorum-sensing behaviour. Local conditions on a microscopic scale may affect signal molecule longevity, stability and accumulation, and this could be used to give information in addition to cell density. Furthermore, in many Gram-negative bacteria, AHL signalling is subservient to an additional two-component signalling system dependent upon homologues of GacS and GacA. The signal(s) to which GacS responds are not known, but recent research suggests that a self-produced ligand may be being detected. This review will focus on two well-studied examples of AHL-regulated plant-associated behaviour, Erwinia carotovora and Agrobacterium tumefaciens, to illustrate the complexity of such signalling networks. [source]