Publications

4525

Summary The phylum Chlamydiae contains obligate intracellular bacteria, several of which cause disease in their hosts. Morphological studies have suggested that this group of bacteria may be pathogens of fish, causing cysts in epithelial tissue – epitheliocystis. Recently, the first genetic evidence of a chlamydial aetiology of this disease in seawater reared Atlantic salmon from Norway and Ireland was presented, and the agent was given the name ‘ Candidatus Piscichlamydia salmonis’. In this article we present molecular evidence for the existence of a novel Chlamydiae that also may cause epitheliocystis in Norwegian salmonids. This novel Chlamydiae has been found in salmonid fish from freshwater, and based on its partial 16S rRNA gene, it may constitute a third genus in the family Chlamydiaceae , or a closely related sister family. By using whole‐mount RNA–RNA hybridization we demonstrate how infected cells are distributed in a patchy manner on a gill arch. The morphology of the novel Chlamydiae includes the characteristic head‐and‐tail cells that have been described earlier from salmonid fish suffering from epitheliocystis. We propose the name ‘ Candidatus Clavochlamydia salmonicola’ for this agent of epitheliocystis in freshwater salmonids.

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.