HOST-DERIVED AMINO-ACIDS SUPPORT THE PROLIFERATION OF SYMBIOTIC BACTERIA

Animals are typically colonized by diverse bacterial symbionts, many o f which are commensal and, in numerous cases, even essential for their host's proper development and growth. In exchange, the host must supp ly a sufficient array and quantity of nutrients to support the prolife ration and persistence of its microbial community. In this investigati on, we have examined such a nutritional environment by determining the symbiotic competence of auxotrophic mutants of the bioluminescent bac terium Vibrio fischeri, and have demonstrated that the host squid Eupr ymna scolopes provides at least 9 aa to the growing culture of symbiot ic V. fischeri present in its light-emitting organ. We also collected and analyzed the extracellular fluid from this organ, in which the sym bionts reside, and confirmed that it contained significant amounts of amino acids, The combined results suggested that host-derived free ami no acids, as well as peptides or proteins, are a source of the amino a cids that support the growth of the symbionts. This work describes a t echnique to sample the symbionts and their surrounding environment wit hout contamination by host tissue components and, in combination with molecular genetic studies, allows the characterization of the nutritio nal conditions that support a cooperative animal-bacterial symbiosis.