The Science Seminar Series: november 12, 2009
Chemically mediated defense of the marine bryozoan, Bugula neritina, by its symbiont: bryostatins and their biosynthesis
Nicole Lopanik, Department of Biology
Georgia State University
Time: 4:00 -5:00pm
Despite recent evidence demonstrating that microbial symbionts often produce secondary metabolites found in marine invertebrates, there are few documented instances of these symbiont-synthesized metabolites playing a role in the survival of the host. Larvae of the sessile marine invertebrate Bugula neritina (Bryozoa) are protected by an effective chemical defense. From the larvae, we isolated three bryostatin-class macrocyclic polyketides, including the novel bryostatin 20, that deterred feeding by a common planktivorous fish that co-occurs with B. neritina. A unique uncultured bacterial symbiont of B. neritina, “Candidatus Endobugula sertula”, was hypothesized as the putative source of the bryostatins. Our research has demonstrated that bryostatins are concentrated in the larvae of B. neritina and protect them against predation by fish, and that bryostatin concentrations decrease as B. neritina ages. Furthermore, aposymbiotic B. neritina larvae were not deterrent and lacked bryostatins, suggesting that the bryostatins are most likely produced by “Ca. Endobugula sertula”. We have isolated a polyketide synthase gene cluster from symbiont-enriched samples of B. neritina that may biosynthesize the bryostatins. This cluster has several enzymatic domains that indicate that it is responsible for making characteristic additions to the pre-bryostatin polyketide chain, and some of these have been shown to function in vitro. This research represents the first example from the marine environment of a microbial symbiont producing an anti-predator defense for its host, and in this case, specifically for the host’s larval stage, which is exceptionally vulnerable to predators.