UC San Diego

Conspicuous and soft-bodied planktonic marine invertebrate larvae often use bioactive compounds for defense against predators. Bioactive compounds play a significant role in shaping the host ecology, and in some cases, the molecules are synthesized by microbial symbionts. This dissertation addresses fundamental questions of bioactive metabolite symbioses between metazoans and microbes. The bryozoan Bugula neritina transmits the symbiotic proteobacterium 'Candidatus Endobugula sertula,' via its larvae. E. sertula synthesizes the bryostatins, which protect B. neritina larvae from predation in the environment. Development of a method for simultaneous in situ bryostatin and E. sertula localization demonstrates that embryos are coated with bryostatins before release from adult colonies, and there is an ontogenetic shift in bryostatin concentration and localization throughout the host life cycle. E. sertula is present in all host life stages of the host, suggesting that bryostatin biosynthesis may somehow be regulated, reserved for specific events in the life history, such as the protection of larvae. The second invertebrate studied in this dissertation is the sponge Corticium candelabrum. C. candelabrum possesses tedanolides, anti-tumor polyketides that might possibly be produced by bacteria in the sponge. Two chapters in this dissertation are dedicated to microbial assemblages associated with developing C. candelabrum embryos. Both Archaea and Bacteria are present throughout C. candelabrum embryonic development. Here we identify three specific bacterial taxa, and show that there are likely dozens more, that are vertically transmitted in C. candelabrum and consistently associated with it across space and time. One of these species, a strain of alpha-proteobacterium a-CC01, is present throughout embryogenesis and is also present in swimming larvae. These studies show that C. candelabrum inoculates vertically transmits a specific, diverse microbial community. A main theme linking the studies in this dissertation is vertical transmission of microbes in marine invertebrates. Embryo and larva isolation allows identification of specific microbial associates in marine invertebrates by decreasing the complexity of microbes in a sample. In addition, understanding of microbial assemblages in marine invertebrate embryos and larvae offers valuable insight into how species-specific invertebrate-microbe associations are maintained in the environment