Meeting Abstract
Euprymna scolopes engages in a specific symbiosis with Vibrio fischeri, a bioluminescent bacterium that lives in a specialized light organ in the squid. The cellular immune system of E. scolopes consists of one type of blood cell, the hemocyte. Previous work showed that hemocytes from colonized adult E. scolopes bind closely-related vibrio species, V. fischeri and V. harveyi, at low and high levels respectively. Curing the adult light organ significantly increased hemocyte binding to V. fischeri, suggesting that colonization influences hemocyte recognition of the symbiont. In order to understand hemocyte binding dynamics with bacteria, hemocytes from adults were isolated and co-incubated with V. fischeri, V. harveyi, Photobacterium leognathi, and polystyrene beads. Live cell imaging using confocal microscopy was used to quantify the binding and release of bacteria by hemocytes. These experiments revealed that over a period of 30min, hemocytes bound all species tested, but after binding released a significantly higher percentage of V. fischeri (60%) compared to P. leognathi (41%), V. harveyi (12%) and beads (2.7%). Furthermore, a V. fischeri mutant lacking an outer membrane protein (OmpU) was released less frequently (34%) compared to wild type, suggesting that OmpU or bacterial products that pass through this porin may play a role in facilitating release from hemocytes. These data, along with previous results, suggest that there are both host and symbiont mechanisms to ensure that V. fischeri evades clearance by the host’s cellular innate immune system. Future work will focus on understanding host cell-surface pattern recognition receptors that may be involved with binding of symbiotic and non-symbiotic bacteria, possibly through the detection of microbe-associated molecular patterns.
