Niche-Specific Impact of a Symbiotic Function on the Persistence of Microbial Symbionts within a Natural Host.

UNLABELLED: How the function of microbial symbionts is affected by their population/consortium structure within a host remains poorly understood. The symbiosis established between Euprymna scolopes and Vibrio fischeri is a well-characterized host-microbe association in which the function and structure of V. fischeri populations within the host are known: V. fischeri populations produce bioluminescence from distinct crypt spaces within a dedicated host structure called the light organ. Previous studies have revealed that luminescence is required for V. fischeri populations to persist within the light organ and that deletion of the lux gene locus, which is responsible for luminescence in V. fischeri, leads to a persistence defect. In this study, we investigated the impact of bioluminescence on V. fischeri population structure within the light organ. We report that the persistence defect is specific to crypt I, which is the most developmentally mature crypt space within the nascent light organ. This result provides insight into the structure/function relationship that will be useful for future mechanistic studies of squid-Vibrio symbiosis. In addition, our report highlights the potential impact of the host developmental program on the spatiotemporal dynamics of host-microbe interactions. IMPORTANCE: Metazoan development and physiology depend on microbes. The relationship between the symbiotic function of microbes and their spatial structure within the host environment remains poorly understood. Here we demonstrate, using a binary symbiosis, that the host requirement for the symbiotic function of the microbial symbiont is restricted to a specific host environment. Our results also suggest a link between microbial function and host development that may be a fundamental aspect of the more complex host-microbe interactions.