Identification of the antifungal peptide-containing symbiont of the marine sponge Theonella swinhoei as a novel δ-proteobacterium, Candidatus Entotheonella palauensis

The Pulauan sponge Theonella swinhoei (class Demospongiae, order Lithistida, family Theunllidae) harbors filamentous bacterial symbionts that contain theopalauamide, an antifungal, bicyclic glycopeptide. In this study, the filamentous symbionts were shown to be novel bacteria belonging to the delta-subdivision of proteo-bacteria. The 16S rRNA gene sequence was determined using a combination of denaturing gradient-gel electrophoresis (DGGE) and specific polymerase chain-reaction (PCR) primers, and its source was confirmed by in situ hybridization. In a series of culture experiments, the filamentous bacteria were propagated in a mixed culture on agar plates, Related 16S rRNA gene sequences were isolated from related sponges with slightly different chemistry. The taxonomic status Candidatus Entotheonella palauensis is proposed for the theopalauamide-containing filamentous bacteria from T. swinhoei.