Symbiosis establishment between the marine bacterium Vibrio fischeri and the Hawaiian bobtail squid requires colonization of the host's light organ. Five to six strains of V. fischeri are found within the light organ, and this strain diversity is essential for maintenance of the symbiosis. Differing abilities to colonize the host have been observed among three co-isolated strains. This project addresses the impact of these strains' individual colonization abilities on the strain diversity of the symbiosis.