Determining the Population Threshold for Quorum Sensing in Chromobacterium violaceum

Many gram-negative bacteria use N-acyl homoserine lactones for extracellular signaling. These diffusible signaling molecules bind with proteins from the LuxR family, which are transcriptional regulators. Gene expression is therefore dependent on cellular density. This process is called quorum sensing. In Cltromobacterium violaceum a purple pigment known as violacein is produced in response to this process. In this experiment pigment expression was shown not to be based on nutrient concentrations, but rather on population density. The extracellular signals, called autoinducers, were extracted from a high population culture and used to induce pigment production in a low density, non-pigmented culture.