Intellectual Merit: Microorganisms have profound affects on all aspects of the biology of plants and animals, both through the life history of each individual and over evolutionary time. The symbiosis between the Hawaiian sepiolid squid, Euprymna scolopes, and its luminous bacterial partner, Vibrio fischeri, represents perhaps the most common type of animal-bacterial interaction: the association of Gram-negative bacteria with the apical surfaces of epithelial cells.
Approaches: The research will continue to apply and develop techniques using molecular biology, protein biochemistry and cell biology; light, electron and confocal microscopy; and bacterial molecular genetics and genomics. In this proposal bioinformatic analyses are added, based on new tools: the genome sequence of V. fischeri, an associated Affymetrix microarray, and a 14,000-gene EST database of the light organ of the juvenile host.
Specific goals: In the squid-vibrio system, symbiont-induced morphogenesis of the host is dramatic, involving apoptosis, hemocyte infiltration, cell swelling and tissue regression. These developmental events rely on both common and unique signals from the symbiont. The research addresses the following questions about the specific mechanisms of three modes of signaling and response: (1) Does the NF-kB pathway, the common animal cell-signaling system that responds to bacterial surface molecules, mediate squid development in response to symbiotic V. fischeri? (2) How are the components of the bacterial flagellar complex differentially regulated to ensure both the onset and the persistence of the association? (3) What is the role of luminescence in signaling host development, and does the animal perceive bacterial light production through its blue-light sensing cryptochromes?
Significance: (1) A number of studies have linked the NF-kB pathway to the function of the innate immune system and, independently, to embryonic development. Evidence that the NF-kB pathway is a mediator of light-organ development through a response to V. fischeri surface molecules would provide a direct link between these immunological and developmental responses of animals. (2) Symbiotic bacteria often differentiate into non-flagellated forms when associated with the tissues of their host. A recent paradigm shift suggests that the flagellar secretion apparatus can still remain active, but switches its function, exporting effector proteins that target host cells. (3) Linking the ability of symbionts to persist to their production of light provides a novel mechanism for maintaining specificity and function, as well as suggests a role for cryptochromes in development.
Broader Impacts: Because it is now clear that associations between bacteria and their animal hosts are common, studies of the squid-vibrio system help provide a foundation for future development of this field. As a relatively simple model, the basic biology of the squid-vibrio system provides an ideal way to introduce the public to the underlying concepts of microbial symbiosis. Accordingly, the PIs participate in the production of television and radio programs, as well as popular press articles, focused on animal-bacterial symbioses. The PIs continue to be dedicated to education at all levels; for example, the research proposed here would involve high school students through the Madison Youth Education Program.
