title: "Candidatus Fokinia solitaria", a Novel "Stand-Alone" Symbiotic Lineage of Midichloriaceae (Rickettsiales).
abstract: Recently, the family Midichloriaceae has been described within the bacterial order Rickettsiales. It includes a variety of bacterial endosymbionts detected in different metazoan host species belonging to Placozoa, Cnidaria, Arthropoda and Vertebrata. Representatives of Midichloriaceae are also considered possible etiological agents of certain animal diseases. Midichloriaceae have been found also in protists like ciliates and amoebae. The present work describes a new bacterial endosymbiont, "Candidatus Fokinia solitaria", retrieved from three different strains of a novel Paramecium species isolated from a wastewater treatment plant in Rio de Janeiro (Brazil). Symbionts were characterized through the full-cycle rRNA approach: SSU rRNA gene sequencing and fluorescence in situ hybridization (FISH) with three species-specific oligonucleotide probes. In electron micrographs, the tiny rod-shaped endosymbionts (1.2 x 0.25-0.35 μm in size) were not surrounded by a symbiontophorous vacuole and were located in the peripheral host cytoplasm, stratified in the host cortex in between the trichocysts or just below them. Frequently, they occurred inside autolysosomes. Phylogenetic analyses of Midichloriaceae apparently show different evolutionary pathways within the family. Some genera, such as "Ca. Midichloria" and "Ca. Lariskella", have been retrieved frequently and independently in different hosts and environmental surveys. On the contrary, others, such as Lyticum, "Ca. Anadelfobacter", "Ca. Defluviella" and the presently described "Ca. Fokinia solitaria", have been found only occasionally and associated to specific host species. These last are the only representatives in their own branches thus far. Present data do not allow to infer whether these genera, which we named "stand-alone lineages", are an indication of poorly sampled organisms, thus underrepresented in GenBank, or represent fast evolving, highly adapted evolutionary lineages.
authors.affiliation: Institut für Hydrobiologie, Technische Universität Dresden, Dresden, Germany.|Dipartimento di Biologia, Università di Pisa, Pisa, Italy.
authors.forename: Franziska
authors.initials: F
authors.lastname: Szokoli
authors.affiliation: Department of Cytology and Histology, St. Petersburg State University, St. Petersburg, Russia.
authors.forename: Elena
authors.initials: E
authors.lastname: Sabaneyeva
authors.affiliation: Dipartimento di Biologia, Università di Pisa, Pisa, Italy.
authors.forename: Michele
authors.initials: M
authors.lastname: Castelli
authors.affiliation: Institut für Hydrobiologie, Technische Universität Dresden, Dresden, Germany.
authors.forename: Sascha
authors.initials: S
authors.lastname: Krenek
authors.affiliation: Mikrobiologie, Biologisches Institut II, Albert-Ludwigs Universität Freiburg, Freiburg, Germany.
authors.forename: Martina
authors.initials: M
authors.lastname: Schrallhammer
authors.affiliation: Departamento de Genética, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Carlos A G
authors.initials: CA
authors.lastname: Soares
authors.affiliation: Departamento de Zoologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Inacio D
authors.initials: ID
authors.lastname: da Silva-Neto
authors.affiliation: Institut für Hydrobiologie, Technische Universität Dresden, Dresden, Germany.
authors.forename: Thomas U
authors.initials: TU
authors.lastname: Berendonk
authors.affiliation: Dipartimento di Biologia, Università di Pisa, Pisa, Italy.
authors.forename: Giulio
authors.initials: G
authors.lastname: Petroni
mesh_terms: D020561:Alphaproteobacteria / Q000145:classification / Q000235:genetics / Q000502:physiology*; D019143:Evolution, Molecular; D054884:Host-Pathogen Interactions; D017404:In Situ Hybridization, Fluorescence; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D010247:Paramecium / Q000145:classification / Q000382:microbiology*; D010802:Phylogeny; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D013559:Symbiosis; D062065:Wastewater / Q000469:parasitology*
chemical_list: D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; D062065:Wastewater