We identified different diarrheagenic (DEC)Escherichia

The quorum-sensing (QS) signal autoinducer-2 (AI-2) has been proposed to promote interspecies signaling in a broad range of bacterial species. AI-2 is spontaneously derived from 4,5-dihydroxy-2,3-pentanedione that, along with homocysteine, is produced by cleavage of S-adenosylhomocysteine (SAH) and S-ribosylhomocysteine by the Pfs and LuxS enzymes. Numerous phenotypes have been attributed to AI-2 QS signaling using luxS mutants. We have previously reported that the luxS mutation also affects the synthesis of the AI-3 autoinducer that activates enterohemorrhagic Escherichia coli virulence genes. Here we show that several species of bacteria synthesize AI-3, suggesting a possible role in interspecies bacterial communication. The luxS mutation leaves the cell with only one pathway, involving oxaloacetate and L-glutamate, for de novo synthesis of homocysteine. The exclusive use of this pathway for homocysteine production appears to alter metabolism in the luxS mutant, leading to decreased levels of AI-3. The addition of aspartate and expression of an aromatic amino acid transporter, as well as a tyrosine-specific transporter, restored AI-3-dependent phenotypes in an luxS mutant. The defect in AI-3 production, but not in AI-2 production, in the luxS mutant was restored by expressing the Pseudomonas aeruginosa S-adenosylhomocysteine hydrolase that synthesizes homocysteine directly from SAH. Furthermore, phenotype microarrays revealed that the luxS mutation caused numerous metabolic deficiencies, while AI-3 signaling had little effect on metabolism. This study examines how AI-3 production is affected by the luxS mutation and explores the roles of the LuxS/AI-2 system in metabolism and QS.

The locus of enterocyte effacement (LEE) is a 35.6 kb pathogenicity island inserted in the genome of some bacteria such as enteropathogenic Escherichia coli, enterohemorrhagic E.coli, Citrobacter rodentium, and Escherichia albertii. LEE comprises the genes responsible for causing attaching and effacing lesions, a characteristic lesion that involves intimate adherence of bacteria to enterocytes, a signaling cascade leading to brush border and microvilli destruction, and loss of ions, causing severe diarrhea. It is composed of 41 open reading frames and five major operons encoding a type three system apparatus, secreted proteins, an adhesin, called intimin, and its receptor called translocated intimin receptor (Tir). LEE is subjected to various levels of regulation, including transcriptional and posttranscriptional regulators located both inside and outside of the pathogenicity island. Several molecules were described being related to feedback inhibition, transcriptional activation, and transcriptional repression. These molecules are involved in a complex network of regulation, including mechanisms such as quorum sensing and temporal control of LEE genes transcription and translation. In this mini review we have detailed the complex network that regulates transcription and expression of genes involved in this kind of lesion.

Enteropathogenic Escherichia coli (EPEC) produces a lesion on epithelial cells called the attaching and effacing (AE) lesion. All genes necessary for AE are encoded within the locus of enterocyte effacement (LEE). EPEC also adheres in a characteristic pattern to epithelial cells by forming microcolonies, usually referred to as localized adherence (LA). LA is mediated by the bundle-forming pilus and flagella. The LEE genes are directly activated by the LEE-encoded regulator (Ler). Transcription of Ler is under the control of Per, integration host factor, Fis, BipA, and quorum sensing (QS), specifically through the luxS system. QS activates expression of the LEE genes in EPEC, with QseA activating transcription of ler. Here we report that transcription of the LEE genes and type III secretion are diminished in both luxS and qseA mutants. Transcription of the LEE genes is affected in both mutants mostly during the mid-exponential phase of growth. Transcription of qseA itself is diminished throughout growth in a luxS mutant and is under autorepression. Furthermore, QS activation of type III secretion is independent of per, given that QseA still activates type III secretion in a per mutant strain. Both mutants are deficient in adherence to epithelial cells and form smaller microcolonies. Several factors may contribute to this abnormal behavior: transcription of LEE genes and type III secretion are diminished, and expression of flagella and Per is altered in both mutants. These results suggest that QS is involved in modulating the regulation of the EPEC virulence genes.Enteropathogenic Escherichia coli (EPEC) is a major cause of diarrhea in children in developing countries (29). EPEC is part of a group of pathogens that includes enterohemorrhagic E. coli (EHEC), Citrobacter rodentium, and Hafnia alvei, all of which are able to cause a lesion on the intestinal epithelial cells named the attaching and effacing (AE) lesion. This lesion is characterized by the destruction of the microvilli and rearrangement of the cytoskeleton to form a pedestal-like structure which cups the bacteria individually (21,28,48). The genes involved in the formation of the AE lesion are encoded within a chromosomal pathogenicity island named the locus of enterocyte effacement (LEE) (25). The LEE region contains five major operons, i.e., LEE1, LEE2, LEE3, tir (LEE5), and LEE4