title: Enigmatic dual symbiosis in the excretory organ of Nautilus macromphalus (Cephalopoda: Nautiloidea).
abstract: Symbiosis is an important driving force in metazoan evolution and the study of ancient lineages can provide an insight into the influence of symbiotic associations on morphological and physiological adaptations. In the 'living fossil' Nautilus, bacterial associations are found in the highly specialized pericardial appendage. This organ is responsible for most of the excretory processes (ultrafiltration, reabsorption and secretion) and secretes an acidic ammonia-rich excretory fluid. In this study, we show that Nautilus macromphalus pericardial appendages harbour a high density of a beta-proteobacterium and a coccoid spirochaete using transmission electron microscopy, comparative 16S rRNA sequence analysis and fluorescence in situ hybridization (FISH). These two bacterial phylotypes are phylogenetically distant from any known bacteria, with ammonia-oxidizing bacteria as the closest relatives of the beta-proteobacterium (above or equal to 87.5% sequence similarity) and marine Spirochaeta species as the closest relatives of the spirochaete (above or equal to 89.8% sequence similarity), and appear to be specific to Nautilus. FISH analyses showed that the symbionts occur in the baso-medial region of the pericardial villi where ultrafiltration and reabsorption processes take place, suggesting a symbiotic contribution to the excretory metabolism.
authors.affiliation: UMR 5178 Biologie des Organismes Marins et Ecosystèmes, Département Peuplements et Milieux Aquatiques, Muséum National d'Histoire Naturelle, 55 rue Buffon, 75005 Paris, France. pernice@mnhn.fr
authors.forename: Mathieu
authors.initials: M
authors.lastname: Pernice
authors.forename: Silke
authors.initials: S
authors.lastname: Wetzel
authors.forename: Olivier
authors.initials: O
authors.lastname: Gros
authors.forename: Renata
authors.initials: R
authors.lastname: Boucher-Rodoni
authors.forename: Nicole
authors.initials: N
authors.lastname: Dubilier
mesh_terms: D000825:Animal Structures / Q000382:microbiology*; D000818:Animals; D001483:Base Sequence; D020562:Betaproteobacteria / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D019295:Computational Biology; D017931:DNA Primers; D017404:In Situ Hybridization, Fluorescence; D016013:Likelihood Functions; D046529:Microscopy, Electron, Transmission; D008957:Models, Genetic; D008969:Molecular Sequence Data; D049850:Nautilus / Q000382:microbiology*; D009510:New Caledonia; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013142:Spirochaeta / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D013559:Symbiosis
chemical_list: D017931:DNA Primers; D012336:RNA, Ribosomal, 16S