Diversity of Actinobacteria Associated with the Marine Ascidian Eudistoma toealensis

Ascidians have yielded a wide variety of bioactive natural products. The colonial ascidian Eudistoma toealensis from Micronesia has been identified as the source of a series of staurosporine derivatives, though the exact origin of these derivatives is still unknown. To identify known staurosporine-producing microbes associated with E. toealensis, we analyzed with 16S rRNA gene tag pyrosequencing the overall bacterial community and focused on potential symbiotic bacteria already known from other ascidians or other marine hosts, such as sponges. The described microbiota was one of very high diversity, comprising 43 phyla: two from archaea, 34 described bacterial phyla, and seven candidate bacterial phyla. Many bacteria, which are renowned community members of other ascidians and marine holobionts, such as sponges and corals, were also part of the E. toealensis microbial community. Furthermore, two known producers of indolocarbazoles, Salinispora and Verrucosispora, were found with high abundance exclusively in the ascidian tissue, suggesting that microbial symbionts and not the organism itself may be the true producers of the staurosporines in E. toealensis.