Characterizing the Host and Symbiont Proteomes in the Association between the Bobtail Squid, Euprymna scolopes, and the Bacterium, Vibrio fischeri

The beneficial symbiosis between the Hawaiian bobtail squid, Euprymna scolopes, and the bioluminescent bacterium, Vibrio fischeri, provides a unique opportunity to study host/microbe interactions within a natural microenvironment. Colonization of the squid light organ by V. fischeri begins a lifelong association with a regulated daily rhythm. Each morning the host expels an exudate from the light organ consisting of 95% of the symbiont population in addition to host hemocytes and shed epithelial cells. We analyzed the host and symbiont proteomes of adult squid exudate and surrounding light organ epithelial tissue using 1D- and 2D-polyacrylamide gel electrophoresis and multidimensional protein identification technology (MudPIT) in an effort to understand the contribution of both partners to the maintenance of this association. These proteomic analyses putatively identified 1581 unique proteins, 870 proteins originating from the symbiont and 711 from the host. Identified host proteins indicate a role of the innate immune system and reactive oxygen species (ROS) in regulating the symbiosis. Symbiont proteins detected enhance our understanding of the role of quorum sensing, two-component signaling, motility, and detoxification of ROS and reactive nitrogen species (RNS) inside the light organ. This study offers the first proteomic analysis of the symbiotic microenvironment of the adult light organ and provides the identification of proteins important to the regulation of this beneficial association.