Production of Acyl-Homoserine Lactone Quorum-Sensing Signals by Gram-Negative Plant-Associated Bacteria (original) (raw)
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Journal of Biotechnology, 2001
Quorum sensing (also called autoinduction) is a term that describes an environmental sensing system that allows bacteria to monitor their own population density. Autoinduction relies upon the interaction of a small diffusible signal molecule (the autoinducer) with a transcriptional activator protein to couple gene expression with cell population density. These signal molecules diffuse from bacterial cells and accumulate in the environment as a function of cell growth. Once a threshold concentration is reached, these signals serve as co-inducers to regulate the transcription of (a) set(s) of target genes. In Gram-negative bacteria, most autoinducers belong to the family of N-acylhomoserine lactones (AHLs). The detection of AHLs (or AHL-like activities) has been greatly facilitated by the development of sensitive bioassays that allow fast screening of microorganisms for diffusible signal molecules. AHL or diketopiperazine-mediated cell-cell signalling play roles in regulating different bacterial functions, such as antibiotic biosynthesis, production of virulence factors, exopolysaccharide biosynthesis, bacterial swarming, plasmid conjugal transfer and transition into the stationary phase. Several bacterial species that interact with plants produce AHL-like compounds. In this review, we will summarise the current knowledge about the detection, characterisation and purification of quorum-sensing molecules from plant-associated bacteria. We will also discuss some of the future prospects and biotechnological applications of autoinducers.
Acyl homoserine-lactone quorum-sensing signal generation
Proceedings of the National Academy of Sciences, 1999
Acyl homoserine lactones (acyl-HSLs) are important intercellular signaling molecules used by many bacteria to monitor their population density in quorum-sensing control of gene expression. These signals are synthesized by members of the LuxI family of proteins. To understand the mechanism of acyl-HSL synthesis we have purified the Pseudomonas aeruginosa RhlI protein and analyzed the kinetics of acyl-HSL synthesis by this enzyme. Purified RhlI catalyzes the synthesis of acyl-HSLs from acyl–acyl carrier proteins and S -adenosylmethionine. An analysis of the patterns of product inhibition indicated that RhlI catalyzes signal synthesis by a sequential, ordered reaction mechanism in which S -adenosylmethionine binds to RhlI as the initial step in the enzymatic mechanism. Because pathogenic bacteria such as P. aeruginosa use acyl-HSL signals to regulate virulence genes, an understanding of the mechanism of signal synthesis and identification of inhibitors of signal synthesis has implicati...
Recombinant whole-cell bioluminescence biosensors developed over the last decade have been very useful to discover bacteria that posses an N-acyl-homoserine lactone (acyl-HSL) regulated quorum-sensing (QS) communication system.The acyl-HSLdependent bacterial bioreporter systems, also known as specific biosensors were constructed to respond to the presence of a certain small molecules, in this case acyl-HSLs.These acyl-HSL-dependent specific biosensors have been developed becauseacyl-HSL signalsdo not contain strongly absorbing chromophores and acyl-HSLs are difficult to detect with standard chemical tests.In addition, the problem of acyl-HSL detection is challenging since these signals are produced at very low levels, customarily in the nanomolar to micromolar range. Acyl-HSLbiosensors contain an acyl-HSL signaldependent receptor / regulator protein that is a member of the LuxR-family and a gene coding for a detectable response phenotype, the reporter gene. The expression of the rep...
Detection of quorum-sensing N -acyl homoserine lactone signal molecules by bacterial biosensors
FEMS Microbiology Letters, 2007
Many Gram-negative bacteria use N-acyl homoserine lactones (AHLs) as quorumsensing (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.
Plant molecular biology, 2016
Bacterial quorum sensing (QS) mechanisms play a crucial role in the proper performance and ecological fitness of bacterial populations. Many key physiological processes are regulated in a QS-dependent manner by auto-inducers, like the N-acyl homoserine lactones (AHLs) in numerous Gram-negative bacteria. In addition, also the interaction between bacteria and eukaryotic hosts can be regulated by AHLs. Those mechanisms gained much attention, because of the positive effects of different AHL molecules on plants. This positive impact ranges from growth promotion to induced resistance and is quite contrasting to the rather negative effects observed in the interactions between bacterial AHL molecules and animals. Only very recently, we began to understand the molecular mechanisms underpinning plant responses to AHL molecules. In this review, we gathered the latest information in this research field. The first part gives an overview of the bacterial aspects of quorum sensing. Later we focus ...
Applied and Environmental Microbiology, 2002
Recent reports have shown that several strains of Pseudomonas putida produce N -acylhomoserine lactones (AHLs). These signal molecules enable bacteria to coordinately express certain phenotypic traits in a density-dependent manner in a process referred to as quorum sensing. In this study we have cloned a genomic region of the plant growth-promoting P. putida strain IsoF that, when present in trans , provoked induction of a bioluminescent AHL reporter plasmid. Sequence analysis identified a gene cluster consisting of four genes: ppuI and ppuR , whose predicted amino acid sequences are highly similar to proteins of the LuxI-LuxR family, an open reading frame (ORF) located in the intergenic region between ppuI and ppuR with significant homology to rsaL from Pseudomonas aeruginosa , and a gene, designated ppuA, present upstream of ppuR , the deduced amino acid sequence of which shows similarity to long-chain fatty acid coenzyme A ligases from various organisms. Using a transcriptional p...
N -acyl-l-homoserine lactone signal interception by Escherichia coli
FEMS Microbiology Letters, 2006
N-acyl-L-homoserine lactone (AHL) mediated quorum sensing is a widespread communication system in gram-negative bacteria which regulates a wide range of target genes in a cell density-dependent manner. Although Escherichia coli is not capable of synthesizing AHL molecules because it lacks an AHL synthase encoding gene, it does produce a predicted AHL receptor of the LuxR family, named SdiA. In this work, we used a promoter trap library to screen for E. coli MG1655 promoters whose expression was affected by synthetic N-hexanoyl-L-homoserine lactone (C6-HSL), and we identified six upregulated and nine downregulated promoters, which also responded to synthetic 3-oxo-N-hexanoyl-L-homoserine lactone (3oxo-C6-HSL). The AHL responsiveness of these promoters was eliminated by knock-out of sdiA, and was temperature dependent, since the identified promoters showed a response at 30 1C but not, or only very weakly at 37 1C. In addition, in line with the observed induction of gadA encoding a glutamate decarboxylase, we could demonstrate an increased acid tolerance of E. coli upon exposure to C6-HSL.
FEMS Microbiology Letters, 2008
In Gram-negative bacteria, a typical quorum-sensing (QS) system involves the production and response to N-acyl homoserine lactones (AHLs). It still remains unclear as to how pivotal and conserved AHL QS is in root-colonizing rhizosphere Pseudomonas. We, therefore, performed a systematic study of AHL QS on a set of 50 rice rhizosphere Pseudomonas isolates. We also isolated the AHL QS genes in two representative strains and analyzed the role of AHL QS regulation of various phenotypes. Our results are discussed with the current knowledge of AHL QS of rhizosphere Pseudomonas, implicating a lack of conservation and an unpredictable role played by AHL QS in this group of bacteria.