title: AI-3 synthesis is not dependent on luxS in Escherichia coli.
abstract: 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.
authors.affiliation: University of Texas Southwestern Medical Center, Department of Microbiology, 5323 Harry Hines Blvd., Dallas, TX 75390-9048, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Walters
authors.forename: Marcelo P
authors.initials: MP
authors.lastname: Sircili
authors.forename: Vanessa
authors.initials: V
authors.lastname: Sperandio
mesh_terms: D026905:Amino Acid Transport Systems / Q000235:genetics / Q000378:metabolism; D026921:Amino Acid Transport Systems, Neutral / Q000235:genetics / Q000378:metabolism; D001224:Aspartic Acid / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D013437:Carbon-Sulfur Lyases; D019453:Escherichia coli O157 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006714:Homoserine / Q000031:analogs & derivatives / Q000235:genetics / Q000378:metabolism; D007783:Lactones / Q000378:metabolism; D009154:Mutation; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism
chemical_list: D026905:Amino Acid Transport Systems; D026921:Amino Acid Transport Systems, Neutral; C063201:AroP protein, E coli; D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C457340:LEE protein, E coli; D007783:Lactones; C091088:N-octanoylhomoserine lactone; D010750:Phosphoproteins; C057333:tyrP protein, E coli; D001224:Aspartic Acid; D006714:Homoserine; D013437:Carbon-Sulfur Lyases; C117753:LuxS protein, Bacteria