Publications

4495

Abstract ‘Candidatus Endobugula sertula,’ the uncultivated γ-proteobacterial symbiont of the marine bryozoan Bugula neritina, synthesizes bryostatins, complex polyketides that render B. neritina larvae unpalatable to predators. Although the symbiosis is well described, little is known about the locations of ‘E. sertula’ or the bryostatins throughout larval settlement, metamorphosis and early development. In this study, we simultaneously localized ‘E. sertula’ and the bryostatins in multiple stages of the B. neritina life cycle, using a novel bryostatin detection method based on its known ability to bind mammalian protein kinase C. Our results suggest that the bryostatins are deposited onto the exterior of B. neritina larvae during embryonic development, persist on the larval surface throughout metamorphosis and are shed prior to cuticle formation. During metamorphosis, ‘E. sertula’ remains adhered to the larval pallial epithelium and is incorporated into the preancestrula cystid tissue layer, which ultimately develops into a bud and gives rise to the next zooid in the colony. Colocalization of bryostatin signal with aggregates of ‘E. sertula’ in buds of ancestrulae suggested new synthesis of bryostatins in ancestrulae. In adult B. neritina colonies, symbiont microcolonies were observed in the funicular cords of rhizoids, which likely result in asexual transmission of ‘E. sertula’ to regenerated colonies. Furthermore, bryostatin signal was detected on the surface of the rhizoids of adult B. neritina colonies. Through simultaneous localization of the bryostatins and the ‘E. sertula,’ we determined how ‘E. sertula’ is transmitted, and identified shifts in bryostatin localization throughout the life cycle of the host B. neritina.

A polyphasic study was undertaken to clarify the taxonomic position of endospore-forming strains 433-D9, 433-E17 and 121-X1. BOX-PCR-generated fingerprints indicated that they may be members of a single species. 16S rRNA gene sequence similarity demonstrated that a representative of this group, 433-D9, is affiliated closely with Bacillus arvi DSM 16317T (100 %), Bacillus arenosi DSM 16319T (99.8 %) and Bacillus neidei NRRL BD-87T (97.1 %). Sequence similarities revealed Bacillus pycnus NRRL NRS-1691T and several Kurthia species as the next nearest relatives. DNA–DNA hybridization results showed that strain 433-D9 is a member of B. arvi. Detection of l-Lys–d-Asp-based peptidoglycan in strain 433-D9, B. arvi DSM 16317T and B. arenosi DSM 16319T was in agreement with their close relationship, but differentiated these strains from B. neidei NRRL BD-87T and B. pycnus NRRL NRS-1691T, for which l-Lys–d-Glu was reported. A similar quinone system was detected in strains 433-D9, 433-E17, 121-X1, B. arvi DSM 16317T, B. arenosi DSM 16319T and B. neidei NRRL BD-87T. This system, unusual for bacilli, consisted of the major compound menaquinone MK-8 (69–80 %) and moderate amounts of MK-7 (19–30 %). This observation was in contrast to the predominance of MK-7 of the closest relative B. pycnus NRRL NRS-1691T, as also reported for representatives of the closely related non-endospore-forming genus Kurthia. Strains 433-D9, B. arvi DSM 16317T and B. arenosi DSM 16319T exhibited homogeneous and discriminative polar lipid profiles and fatty acid profiles consisting of major acids i-C15 : 0 and ai-C15 : 0 and moderate amounts of i-C17 : 1 ω10c and i-C17 : 1 I/ai-C17 : 1 B that discriminated them from closely related strains such as B. neidei NRRL BD-87T. On the basis of clear-cut discriminative chemotaxonomic markers, we propose strains 433-D9, 433-E17 and 121-X1, B. arvi DSM 16317T, B. arenosi DSM 16319T and B. neidei NRRL BD-87T to be reclassified within a separate genus. For this new taxon, we propose the name Viridibacillus gen. nov., and we propose the reclassification of Bacillus arvi, Bacillus arenosi and Bacillus neidei as Viridibacillus arvi gen. nov., comb. nov. (the type species of Viridibacillus, with the type strain DSM 16317T =LMG 22165T), Viridibacillus arenosi comb. nov. (type strain DSM 16319T =LMG 22166T) and Viridibacillus neidei comb. nov. (type strain NRRL BD-87T =DSM 15031T =JCM 11077T).