Genomic and biochemical changes during the onset of the squid-Vibrio symbiosis

The newfound recognition that intimate associations between animals and bacteria are the rule rather than the exception has led to the broad question: how are animal-bacterial interactions regulated to produce the alternate outcomes of health and disease? Work presented here uses the Euprymna scolopes-Vibrio fischeri symbiosis, an association in which the bacterial partner colonizes the host light organ, to address one aspect of this question. Specifically, do host cells respond to key factors of the squid-vibrio symbiosis, such as bacterial colonization, autoinducers and bioluminescence? I define the transcriptional profile of organ tissue during early development and colonization and characterize the role of one protein in maintaining specificity of the symbiosis.; To obtain a global view of transcripts expressed in the organ, I annotated and characterized a non-redundant EST database derived from 11 individual cDNA libraries at various times during early development, with and without V. fischeri colonization. Gene ontology categorization of the 13,962 unique transcripts mirrors the structure and function of the organ during early colonization.; To determine how key factors of the symbiosis affect gene expression in the light organ, I used spotted microarrays created from the cDNA library. I compared the transcriptomes of 18-h organs colonized under different conditions of colonization, as well as autoinducer and light exposure. This analysis identified tens to hundreds of transcripts differentially regulated in response to these features.; The oxidative burst pathway is commonly modulated in symbiosis. Sequencing confirmed that critical pathways are present in the organ during the first few days following symbiont colonization. QRT-PCR showed that several pathway members are transcriptionally down-regulated upon initial V. fischeri colonization, whereas bacterial pathogenesis usually up-regulates the activity of these pathways. Immunocytochemistry revealed that the terminal peroxidase, a halide peroxidase (HPO), is expressed in light organ epithelia interfacing with colonizing V. fischeri populations. Finally, the use of HPO inhibitors caused a loss of symbiont specificity.; This thesis makes valuable contributions to the understanding of transcriptional changes in host tissues in response to colonization by a beneficial symbiont. Further, this work provides evidence for a common language used to modulate both beneficial and pathogenic animal-bacterial interactions.