Quorum sensing describes the synthesis and detection of small signaling molecules, called autoinducers (AI), that allow individual bacterial cells to coordinate functions as a group.  Quorum sensing regulates cellular activities that are important for survival within a host, such as biofilm formation and virulence.  Using the mutualism established between the marine bacterium Vibrio fischeri and bobtail squid, I study the ability of segregated bacterial populations to communicate via AI to promote symbiotic function.