BACTERIAL COLONIZATION, INFECTION, AND IMMUNITY IN THE PURPLE SEA URCHIN LARVA
Nicholas Schuh, University of Toronto
Nicholas W. Schuh1, 2, Andreas Heyland2, Jonathan P. Rast1, 3, 4.
1Department of Medical Biophysics, University of Toronto, Toronto, ON;
2Department of Integrative Biology, University of Guelph, Guelph, ON;
3Department of Immunology, University of Toronto, Toronto, ON;
4Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, GA.
Exposure to bacteria during development has wide-ranging effects on animal biology but can also inhibit growth or cause disease. The immune system is the prime mediator of these microbial interactions, and is itself shaped by them. Our group uses larvae of the purple sea urchin (Strongylocentrotus purpuratus) as an experimental model for colonization, immune development, and infection. Previously, we identified multiple larval immunocytes and characterized their functions during exposure to the model pathogen Vibrio diazotrophicus. Subsequently, we have shifted focus to commensal and/or opportunistic larva-associated bacteria isolated from larval samples. We visualize bacterial colonization in larvae with 16S FISH and compare the bacterial microbiomes of larvae raised in ocean water to those of larvae exposed to adult-associated bacteria in the laboratory. This ‘artificial’ microbiome is similar to, but significantly less diverse, than its more natural counterpart. Regardless, bacteria-exposed larvae are significantly more resistant to the larva-associated pathogen Vibrio lentus, which induces a potentially lethal vibriosis by secretion and cleavage of the Zn2+-dependent metalloprotease vibriolysin/Vsm. Other larva-associated bacterial isolates are benign or induce mild IL-17 responses in the midgut epithelium compared to V. diazotrophicus, but at least one Colwellia strain induces a novel pattern of IL-17-4 and IL-17-1 expression in cells around the mouth and throughout the blastocoel. We also discuss ongoing RNA-seq and ISH experiments to profile immune cell behaviour and immune gene expression during colonization by these strains. These results show that larvae recruit specific bacterial communities distinct from their environments, and that these communities influence development and immunity.