ANIMAL BACTERIAL INTERACTIONS IN THE EARLY-LIFE HISTORY OF MARINE-INVERTEBRATES - THE EUPRYMNA-SCOLOPES VIBRIO-FISCHERI SYMBIOSIS

The symbiotic association between the Hawaiian sepiolid squid Euprymna scolopes and the marine luminous bacterium Vibrio fischeri is being d eveloped as a model system for the study of animal-bacterial interacti ons during development. Changes in light organ morphology during embry ogenesis foster successful infection of the light organ with the prope r bacterial partner. These embryonic events of light organ morphogenes is include the elaboration of an epithelial surface with a complex cil iated, microvillous held. The squid host hatches without the bacterial symbionts, but acquires them within hours from the free-living popula tion of the bacteria in the water column. Upon exposure to the proper symbionts, the host organ undergoes a series of morphogenetic changes, including loss of the ciliated, microvillous field. The light organ t hen goes on to mature into a morphological configuration that serves t o promote the maintenance of a stable association with the bacteria an d that correlates with the use of the bacterial bioluminescence in beh avior of the host. This symbiosis is discussed in light of other cycli cally transmitted animal-bacterial associations.