Identification of sibling species of the bryozoan Bugula neritina that produce different anticancer bryostatins and harbor distinct strains of the bacterial symbiont "Candidatus endobugula sertula"

Although the cosmopolitan marine bryozoan Bugula neritina is recognized as a single species, natural products from this bryozoan vary among population s. B. neritina is the source of the anticancer drug candidate bryostatin i, but it also produces other bryostatins, and different populations contain different bryostatins. We defined two chemotypes on the basis of previous s tudies: chemotype: O contains bryostatins with an octa-2,4-dienoate substit uent (including bryostatin i), as well as other bryostatins; chemotype M la cks bryostatins with the octa-2,4-dienoate substituent. B. neritina contain s a symbiotic gamma-proteobacterium "Candidatus Endobugula sertula,'' and i t has been proposed that bryostatins may be synthesized by bacterial symbio nts. In this study, B. neritina populations along the California coast were sampled for genetic variation and bryostatin content. Colonies that differ in chemotype also differ genetically by 8% in the mitochondrial cytochrome c oxidase subunit 1 (CO I) gene; this difference is sufficient to suggest that the chemotypes represent different species. Each species contains a di stinct strain of "E. sertula" that differs at four nucleotide sites in the small subunit ribosomal RNA (SSU rRNA) gene. These results indicate that th e chemotypes have a genetic basis rather than an environmental cause. Gene sequences from an Atlantic sample matched sequences from the California che motype M colonies, suggesting that this type may be cosmopolitan due to tra nsport on boat hulls.