AUTHOR=Kroer Paul , Kjeldsen Kasper U. , Nyengaard Jens R. , Schramm Andreas , Funch Peter 

TITLE=A Novel Extracellular Gut Symbiont in the Marine Worm Priapulus caudatus (Priapulida) Reveals an Alphaproteobacterial Symbiont Clade of the Ecdysozoa

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.00539

DOI=10.3389/fmicb.2016.00539

ISSN=1664-302X

ABSTRACT=<p><italic>Priapulus caudatus</italic> (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 <italic>in situ</italic> hybridization (FISH) identified them as extracellular, elongate bacteria closely associated with the microvilli, for which we propose the name “<italic>Candidatus</italic> Tenuibacter priapulorum”. Within Rickettsiales, they form a phylogenetically well-defined, family-level clade with uncultured symbionts of marine, terrestrial, and freshwater arthropods. <italic>Cand</italic>. 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.</p>