title: A Novel Extracellular Gut Symbiont in the Marine Worm Priapulus caudatus (Priapulida) Reveals an Alphaproteobacterial Symbiont Clade of the Ecdysozoa.
abstract: Priapulus caudatus (phylum Priapulida) is a benthic marine predatory worm with a cosmopolitan distribution. In its digestive tract we detected symbiotic bacteria that were consistently present in specimens collected over 8 years from three sites at the Swedish west coast. Based on their 16S rRNA gene sequence, these symbionts comprise a novel genus of the order Rickettsiales (Alphaproteobacteria). Electron microscopy and fluorescence in situ hybridization (FISH) identified them as extracellular, elongate bacteria closely associated with the microvilli, for which we propose the name "Candidatus Tenuibacter priapulorum". Within Rickettsiales, they form a phylogenetically well-defined, family-level clade with uncultured symbionts of marine, terrestrial, and freshwater arthropods. Cand. Tenuibacter priapulorum expands the host range of this candidate family from Arthropoda to the entire Ecdysozoa, which may indicate an evolutionary adaptation of this bacterial group to the microvilli-lined guts of the Ecdysozoa.
authors.affiliation: Section for Genetics, Ecology, and Evolution, Department of Bioscience, Aarhus University Aarhus, Denmark.
authors.forename: Paul
authors.initials: P
authors.lastname: Kroer
authors.affiliation: Section for Microbiology and Center for Geomicrobiology, Department of Bioscience, Aarhus University Aarhus, Denmark.
authors.forename: Kasper U
authors.initials: KU
authors.lastname: Kjeldsen
authors.affiliation: Stereology and Electron Microscopy Laboratory, Department of Clinical Medicine, Centre for Stochastic Geometry and Advanced Bioimaging, Aarhus University Aarhus, Denmark.
authors.forename: Jens R
authors.initials: JR
authors.lastname: Nyengaard
authors.affiliation: Section for Microbiology and Center for Geomicrobiology, Department of Bioscience, Aarhus University Aarhus, Denmark.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schramm
authors.affiliation: Section for Genetics, Ecology, and Evolution, Department of Bioscience, Aarhus University Aarhus, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Funch
keywords: Ecdysozoa; Priapulus caudatus; Rickettsiales; gut symbiont; invertebrate-bacteria symbiosis; microvilli