The LuxS-dependent autoinducer AI-2 controls the expression of an ABC transporter that functions in AI-2 uptake in Salmonella typhimurium

Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014, USA.
Molecular Microbiology (Impact Factor: 4.42). 12/2001; 42(3):777-93.
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In a process called quorum sensing, bacteria communicate with one another using secreted chemical signalling molecules termed autoinducers. A novel autoinducer called AI-2, originally discovered in the quorum-sensing bacterium Vibrio harveyi, is made by many species of Gram-negative and Gram-positive bacteria. In every case, production of AI-2 is dependent on the LuxS autoinducer synthase. The genes regulated by AI-2 in most of these luxS-containing species of bacteria are not known. Here, we describe the identification and characterization of AI-2-regulated genes in Salmonella typhimurium. We find that LuxS and AI-2 regulate the expression of a previously unidentified operon encoding an ATP binding cassette (ABC)-type transporter. We have named this operon the lsr (luxS regulated) operon. The Lsr transporter has homology to the ribose transporter of Escherichia coli and S. typhimurium. A gene encoding a DNA-binding protein that is located adjacent to the Lsr transporter structural operon is required to link AI-2 detection to operon expression. This gene, which we have named lsrR, encodes a protein that represses lsr operon expression in the absence of AI-2. Mutations in the lsr operon render S. typhimurium unable to eliminate AI-2 from the extracellular environment, suggesting that the role of the Lsr apparatus is to transport AI-2 into the cells. It is intriguing that an operon regulated by AI-2 encodes functions resembling the ribose transporter, given recent findings that AI-2 is derived from the ribosyl moiety of S-ribosylhomocysteine.

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Available from: Julia Semmelhack, Oct 10, 2015
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    • "NCBI QS (AI-2) luxS (8134173) S-Ribosylhomocysteinase; QS autoinducer-2 production Schauder et al. (2001); Taga et al. (2001) Genes regulated by QS rsmA (8134182) "
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    ABSTRACT: Several studies have reported effects of the plant phenolic acids cinnamic acid (CA) and salicylic acid (SA) on virulence of soft rot enterobacteria. However, the mechanisms involved in these processes are not yet fully understood. Here, we investigated whether CA and SA interfere with the quorum-sensing (QS) system of two Pectobacterium species, P. aroidearum and P. carotovorum subsp brasiliense, which are known to produce N-acyl-homoserine lactone (AHL) QS signals. Our results clearly indicate that both phenolic compounds affect the QS machinery of the two species, consequently altering the expression of bacterial virulence factors. While in control treatments, expression of QS-related genes increased over time, exposure of bacteria to nonlethal concentrations of CA or SA inhibited the expression of QS genes, including expI, expR, PC1_1442 (luxR transcriptional regulator) and luxS (a component of the AI-2 system). Other virulence genes known to be regulated by the QS system, such as pecS, pel, peh and yheO, were also down-regulated relative to the control. In agreement with the low levels of expression of expI and expR, CA and SA also reduced the level of AHL signal. The effects of CA and SA on AHL signaling were confirmed in compensation assays, in which exogenous application of N-(β-ketocaproyl)-L-homoserine lactone (eAHL) led to the recovery of the reduction in virulence caused by the two phenolic acids. Collectively, the results of gene expression studies, bioluminescence assays, virulence assays and compensation assays with eAHL clearly support a mechanism by which CA and SA interfere with Pectobacterium virulence via the QS machinery. This article is protected by copyright. All rights reserved.
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    • "S-Ribosylhomocysteine lyase is encoded by luxS gene and is involved in the synthesis of autoinducer 2 (Al-2), which is secreted by bacteria during quorum sensing [64, 65]. Changes in the cell density during the transition of growth phases are likely to stimulate the expression of S-ribosylhomocysteine lyase and the subsequent synthesis of Al-2 in L. lactis M4. "
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    ABSTRACT: Lactococcus lactis is the most studied mesophilic fermentative lactic acid bacterium. It is used extensively in the food industry and plays a pivotal role as a cell factory and also as vaccine delivery platforms. The proteome of the Malaysian isolated L. lactis M4 dairy strain, obtained from the milk of locally bred cows, was studied to elucidate the physiological changes occurring between the growth phases of this bacterium. In this study, ultraperformance liquid chromatography nanoflow electrospray ionization tandem mass spectrometry (UPLC- nano-ESI-MS(E)) approach was used for qualitative proteomic analysis. A total of 100 and 121 proteins were identified from the midexponential and early stationary growth phases, respectively, of the L. lactis strain M4. During the exponential phase, the most important reaction was the generation of sufficient energy, whereas, in the early stationary phase, the metabolic energy pathways decreased and the biosynthesis of proteins became more important. Thus, the metabolism of the cells shifted from energy production in the exponential phase to the synthesis of macromolecules in the stationary phase. The resultant proteomes are essential in providing an improved view of the cellular machinery of L. lactis during the transition of growth phases and hence provide insight into various biotechnological applications.
    03/2014; 2014(12):642891. DOI:10.1155/2014/642891
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    • "After binding, the Lsr ABC transporter that consists of LsrC and LsrA transports AI-2 into the cell where it is phosphorylated by LsrK. AI-2 in its phosphorylated form interacts with the LsrR that is a transcriptional repressor, in order to alleviate repression of the operon lsr which may up regulate other operons (Taga et al., 2001). In Gram-negative and Gram-positive bacteria a wide range of LuxS/AI-2 systems have been found which has proposed the idea that the AI-2 system is utilized for cross-species signaling process by organisms that live in mixed-species communities like biofilms (Xavier and Bassler, 2003). "
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