Comparative genomics of Vibrio fischeri populations sampled from Hawaii.. A genomic comparison of 13 Vibrio fischeri isolatesin the perspective of their symbiotic ecology

The luminous marine bacterium Vibrio fischeri is the natural symbiont of the Hawaiian bobtail squid, Euprymna scolopes. Two distinct populations of squids have been described on different sides of the island of Oahu: in eastern Kaneohe Bay (KB), and southern Maunaloa Bay (MB). We sequenced the genomes of eleven previously described squid symbionts, isolated from adult KB or MB animals. In addition, the relative colonization ability of these isolates was compared by performing co-colonization competition assays with juvenile squid from either the KB or MB populations. Our aim was to look for evidence of partner choice by examining whether the geographic origins of a squid-bacterium combination influenced their colonization effectiveness. No relationship was found between where the partners were isolated and how well they initiated a colonization; instead, symbionts from both KB and MB animals fell into two groups based on their tendency to form exclusive associations. We compared the genomes of all these V. fischeri strains, as well as one obtained from the light organ of the Japanese pinecone fish, to both assess their genomic diversity, and identify candidate genes specifically involved in symbiotic colonization of the squid light organ. Taken together, the results indicate the presence of a link between the genome content of V. fischeri strains and their dominance in the ecologically relevant niche of symbiosis.