Analysis of LuxR Regulon Gene Expression during Quorum Sensing inVibrio fischeri

Abstract

The regulation of the lux operon (luxICDABEG) of Vibrio fischeri has been intensively studied as a model for quorum sensing in proteobacteria. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis previously identified several non-Lux proteins in V. fischeri MJ-100 whose expression was dependent on LuxR and 3-oxo-hexanoyl-L-homoserine lactone (3-oxo-C6-HSL). To determine if the LuxR-dependent regulation of the genes encoding these proteins was due to direct transcriptional control by LuxR and 3-oxo-C6-HSL or instead was due to indirect control via an unidentified regulatory element, promoters of interest were cloned into a lacZ reporter and tested for their LuxR and 3-oxo-C6-HSL dependence in recombinant Escherichia coli. The promoters for qsrP, acfA, and ribB were found to be directly activated via LuxR-3-oxo-C6-HSL. The sites of transcription initiation were established via primer extension analysis. Based on this information and the position of the lux box-binding site near position ؊40, all three promoters appear to have a class II-type promoter structure. In order to more fully characterize the LuxR regulon in V. fischeri MJ-100, real-time reverse transcription-PCR was used to study the temporal expression of qsrP, acfA, and ribB during the exponential and stationary phases of growth, and electrophoretic mobility shift assays were used to compare the binding affinities of LuxR to the promoters under investigation. Taken together, the results demonstrate that regulation of the production of QsrP, RibB, and AcfA is controlled directly by LuxR at the level of transcription, thereby establishing that there is a LuxR regulon in V. fischeri MJ-100 whose genes are coordinately expressed during mid-exponential growth.

A Novel Plant Ferredoxin-Like Protein and the Regulator Hor Are Quorum-Sensing Targets in the Plant Pathogen Erwinia carotovora

“…Recent transcriptome and proteome analysis have expanded our knowledge of the QS regulons of different gram-negative bacteria (Chen et al 2003;Qin et al 2007;Schuster et al 2003;Wagner et al 2003). These studies reveal that, in many cases, QS is a global regulatory system affecting a diverse set of both physiological and metabolic processes (e.g., in Pseudomonas aeruginosa, over 400 genes are controlled by QS).…”

Transcriptome Analysis of the Vibrio fischeri LuxR-LuxI Regulon

“…One interpretation of our inability to demonstrate LuxR binding to the other four promoters in vitro is that they are low-affinity LuxR binding targets. Experiments were performed as previously described (28,37). Reaction mixtures contained 1 fmol of DNA, 6 M 3OC6-HSL, and either no LuxR (Ϫ) or LuxR at a final concentration of 6.2 nM (ϩ).…”

The Function of Cyclo(Phe-Pro) in Gene Expression of Vibrio Harveyi

“…Population size is implied by the concentration of autoinducers, so that way there are enough cells to produce an appropriate response, such as produce enough bioluminescence to be seen or produce enough toxin to affect the host (Qin et al 2007). So genes controlled by quorum sensing are not directly under the influence of population size or cell-density, but on autoinducer concentration, which in nature is a function of those parameters.…”

“…The quorum sensing molecules were first known as autoinducers (Nealson et al 1970, Qin et al 2007. Each bacteria species that modulates its gene expression on the basis of celldensity has their own signaling molecule.…”

“…These messages trigger the bacteria's genetic response to external stimuli that concern survival, propagation, and virulence in certain species. Most quorum sensing communication is intraspecific, but certain signals are thought to be used for inter-specific communication (Park et al 2006, Qin et al 2007). …”