title: Autoinducers act as biological timers in Vibrio harveyi.
abstract: Quorum sensing regulates cell density-dependent phenotypes and involves the synthesis, excretion and detection of so-called autoinducers. Vibrio harveyi strain ATCC BAA-1116 (recently reclassified as Vibrio campbellii), one of the best-characterized model organisms for the study of quorum sensing, produces and responds to three autoinducers. HAI-1, AI-2 and CAI-1 are recognized by different receptors, but all information is channeled into the same signaling cascade, which controls a specific set of genes. Here we examine temporal variations of availability and concentration of the three autoinducers in V. harveyi, and monitor the phenotypes they regulate, from the early exponential to the stationary growth phase in liquid culture. Specifically, the exponential growth phase is characterized by an increase in AI-2 and the induction of bioluminescence, while HAI-1 and CAI-1 are undetectable prior to the late exponential growth phase. CAI-1 activity reaches its maximum upon entry into stationary phase, while molar concentrations of AI-2 and HAI-1 become approximately equal. Similarly, autoinducer-dependent exoproteolytic activity increases at the transition into stationary phase. These findings are reflected in temporal alterations in expression of the luxR gene that encodes the master regulator LuxR, and of four autoinducer-regulated genes during growth. Moreover, in vitro phosphorylation assays reveal a tight correlation between the HAI-1/AI-2 ratio as input and levels of receptor-mediated phosphorylation of LuxU as output. Our study supports a model in which the combinations of autoinducers available, rather than cell density per se, determine the timing of various processes in V. harveyi populations.
authors.affiliation: Munich Center for integrated Protein Science at the Department of Biology I, Microbiology, Ludwig-Maximilians-Universität Munich, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Anetzberger
authors.forename: Matthias
authors.initials: M
authors.lastname: Reiger
authors.forename: Agnes
authors.initials: A
authors.lastname: Fekete
authors.forename: Ursula
authors.initials: U
authors.lastname: Schell
authors.forename: Nina
authors.initials: N
authors.lastname: Stambrau
authors.forename: Laure
authors.initials: L
authors.lastname: Plener
authors.forename: Joachim
authors.initials: J
authors.lastname: Kopka
authors.forename: Phillippe
authors.initials: P
authors.lastname: Schmitt-Kopplin
authors.forename: Hubert
authors.initials: H
authors.lastname: Hilbi
authors.forename: Kirsten
authors.initials: K
authors.lastname: Jung
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D053038:Quorum Sensing / Q000502:physiology; D014733:Vibrio / Q000378:metabolism* / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins