Regulation of Host Colonization Specificity

Overview: Page A Microbial symbioses are prevalent in animals and are crucial to the health and development of both partners. These relationships have evolved robust mechanisms to ensure the faithful transmission of symbionts during each new host generation. This proposal applies modern genomic and genetic methods to examine how host specificity develops in a horizontally transmitted animal-microbe symbiosis. The question of colonization fidelity is fundamental to understanding microbial transmission in beneficial and pathogenic colonization, the animal host range of symbiotic bacteria, the maintenance of microbial diversity, and the influence of environmental factors (e.g., climate change) on host-symbiont coevolution. By taking an integrative approach that encompasses natural populations, genomes, pathways, and genes, this proposal seeks to understand the molecular mechanisms that maintain symbiont-host fidelity and facilitate co-evolutionary dynamics in horizontally-transmitted bacterial symbionts. Intellectual Merit : The proposal focuses on the binary association between Vibrio fischeri bacteria and the bobtail squid hosts. Preliminary data have revealed the importance of biofilm formation (bacterial aggregation) during host colonization, both in V. fischeri colonization of squid and in many bacterial colonization systems. In the canonical squid symbiont ES114, the RscS sensor kinase activates biofilm genes that are necessary for normal host colonization. We have identified two classes of symbionts that are closely related to ES114 but that use distinct mechanisms. The first uses a completely novel system for colonization, whereas the second uses the same biofilm target genes without the known regulator. To study how evolutionary changes in bacterial signal transduction influence the robustness of partner stability as a mutualism evolves, we will use the two comparative systems and evaluate the hypotheses that (i) small genetic changes fundamentally alter the manner by which microbes interact with animals, and (ii) changes in bacterial aggregation form the basis for multiple evolutionary transitions in host partner choice. To test these hypotheses we will determine the genetic factors that regulate biofilm formation and host colonization in each strain and we will evaluate the manner by which each genetic lesion influences biofilm signal transduction across V. fischeri strains. Completion of these objectives will advance our understanding of how biofilm formation, an important bacterial behavior, influences the development and evolution of partner choice during symbiotic colonization. Broader Impacts : This work examines closely-related bacterial symbionts to identify how partnerships with animals evolve. The ability to study bacterial genetic networks at high resolution will be applicable to understanding how signaling pathways in bacteria respond to other shifts, such as those introduced by climate change or other ecological processes. This will be accomplished with unique training opportunities that involve undergraduate and doctoral students in high-throughput modern methods such as bacterial genome sequencing, genome assembly, and the associated computational skills. A pilot workshop is proposed that integrates with the research aims and trains undergraduate and graduate students in modern bioinformatics techniques. A plan is presented to disseminate results locally, regionally, and nationally; at the regional level a new beneficial microbes symposium is proposed to enhance research