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. Vibrio fischeri is a bacterial symbiont of the Hawaiian bobtail squid Euprymna scolopes 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 Δlux mutant, which lacks several genes within the lux operon that are necessary for bioluminescence production, and a LuxI− mutant, which cannot synthesize the quorum signaling molecule N-3-oxohexanoyl-homoserine lactone. Here, we build upon that observation and show that populations of LuxI− feature elevated promoter activity for the lux operon. We find that population structures comprising of Δlux and LuxI− are attenuated within the squid, but a wild-type strain enables the LuxI− strain type to be maintained in vivo. 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.
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