INVESTIGATING MECHANISMS OF SPECIFICITY IN A BIOLUMINESCENT VERTEBRATE-BACTERIA SYMBIOSIS

Project SummaryInvestigating mechanisms of specificity in a vertebrate-bacteria symbiosisDespite an increased awareness of the importance of the microbiome to human health and disease, relativelylittle is known about the molecular mechanisms employed by symbiotic bacteria to stably colonize the gut, asthey are difficult to disentangle and experimentally study in isolation. There are several established modelsystems used to explore specific pathways and processes underpinning symbiotic associations, however,none represent a naturally evolved, binary symbiosis between a vertebrate host and a single bacterialspecies. A major, long-term objective of this study is to establish the bioluminescent symbiosisbetween a coral reef fish (Siphamia tubifer) and a luminous bacterium in the Vibrio family,(Photobacterium mandapamensis) as a model association to define the mechanisms involved inregulating specificity and colonization in a gut-associated symbiosis. The results of this project willprovide new insights on the evolution of stable interactions between vertebrate hosts and beneficial bacteriaand can be compared across model hosts to further define the universal principals underlying animal-microbeassociations.The overall objective of this project is to investigate how the specificity of vertebrate-bacteria associations ismaintained from a broad evolutionary scale down to the molecular level by addressing the following researchaims: 1) Define the degree of specificity of the Siphamia?Photobacterium symbiosis, 2) Characterizethe infection dynamics and symbiont competition within a host light organ, and 3) Identify keymechanisms involved in the establishment and persistence of the symbiosis. To do so, the specificity ofthe symbiosis will first be broadly defined across all 23 species in the host fish genus, then across the broadgeographic distribution of a single host species, S tubifer. The specificity of the S. tubifer-P. mandapamensisassociation will then be tested in culture to determine whether it is regulated by local environmental andecological factors or conserved at a more molecular level. Next, the intra-species symbiont diversity will beexperimentally tested to better understand strain competition and infection dynamics within a host. Finally,the genetic mechanisms involved in regulating the symbiosis will be determined by comparing both host andsymbiont gene expression throughout the infection process. Overall this study will reveal the processes thatregulate the establishment and maintenance of specific associations between vertebrate hosts and beneficialbacteria across multiple timescales, and in doing so, will provide the greater research community with a novelbinary vertebrate-bacteria model system with which to deepen our understanding of these vital interactions.