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.

Combinatorial quorum sensing allows bacteria to resolve their social and physical environment

“…However, unlike our model, it does not offer a rationale for investment in these molecules, which are arguably better interpreted as by-product cues that may advertise a cell's presence to competitors instead of being a signal in an evolutionary sense (21). More recently, it has been proposed that, if autoinducers naturally accumulate in a sequential order during single-species population growth, bacteria can distinguish phases in population development from total signal concentration (22,23). A last possibility is that multiple signals simply allow for multiple thresholds for gene expression if bacteria require information on multiple-density thresholds (24).…”

Microbiome shifts and the inhibition of quorum sensing by Black Band Disease cyanobacteria

“…The consequences of manipulation of Vibrio QS with the cyanobacterial compound lyngbic acid are not yet known. In Vibrio spp., QS signals act as timers, with the CqsS/CAI-1 system active at low population densities (Henke and Bassler, 2004;Anetzberger et al, 2012). In concert with other QS signals, the CqsS/CAI-1 system regulates toxin and metalloprotease production, as well as type 3 secretion system (Henke and Bassler, 2004;Higgins et al, 2007).…”

Determination of Extracellular Molecules Produced by Vibrio Harveyi Using MS/MS

“…There was a gradual increase in the intensity of HAI-1 throughout the growth curve, indicating an accumulation in the media, although there is a sharper increase during the 20-24 hour interval. The concentration of HAI-1 was low compared to other molecules detected, which agree with findings by Anetzberger et al (2012), which showed that the concentrations of autoinducers vary depending on the growth phase. The study showed that HAI-1 and CAI-1 activities becomes more prominent later during stationary phase, and that AI-2 concentration accumulates early during growth, peaks during mid-exponential growth phase and eventually declines during stationary phase.…”