Quorum sensing facilitates interpopulation signaling by within the light organ of .

Quorum sensing is an intercellular signaling mechanism that enables bacterial cells to coordinate population-level behaviors. How quorum sensing functions in natural habitats remains poorly understood. is a bacterial symbiont of the Hawaiian bobtail squid and depends on LuxI/LuxR quorum sensing to produce the symbiotic trait of bioluminescence. A previous study demonstrated that animals emit light when co-colonized by a Δ mutant, which lacks several genes within the operon that are necessary for bioluminescence production, and a LuxI mutant, which cannot synthesize the quorum signaling molecule -3-oxohexanoyl-homoserine lactone. Here, we build upon that observation and show that populations of LuxI feature elevated promoter activity for the operon. We find that population structures comprising of Δ and LuxI are attenuated within the squid, but a wild-type strain enables the LuxI strain type to be maintained . These experimental results support a model of interpopulation signaling, which provides basic insight into how quorum sensing functions within the natural habitats found within a host.