Sarah Regi

Document Type

Honors Project

First Advisor

Dr. Stephen Baron

Degree Award Date

Spring 2002


Population Threshold, Quorum Sensing, Chromobacterium violaceum


Bacteriology | Biology | Laboratory and Basic Science Research | Microbiology


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.