title: New insights into the evolution of Wolbachia infections in filarial nematodes inferred from a large range of screened species.
abstract: BACKGROUND
  Wolbachia are intriguing symbiotic endobacteria with a peculiar host range that includes arthropods and a single nematode family, the Onchocercidae encompassing agents of filariases. This raises the question of the origin of infection in filariae. Wolbachia infect the female germline and the hypodermis. Some evidences lead to the theory that Wolbachia act as mutualist and coevolved with filariae from one infection event: their removal sterilizes female filariae; all the specimens of a positive species are infected; Wolbachia are vertically inherited; a few species lost the symbiont. However, most data on Wolbachia and filaria relationships derive from studies on few species of Onchocercinae and Dirofilariinae, from mammals.
  
  
  RESULTS
  We investigated the Wolbachia distribution testing 35 filarial species, including 28 species and 7 genera and/or subgenera newly screened, using PCR, immunohistochemical staining, whole mount fluorescent analysis, and cocladogenesis analysis. (i) Among the newly screened Onchocercinae from mammals eight species harbour Wolbachia but for some of them, bacteria are absent in the hypodermis, or in variable density. (ii) Wolbachia are not detected in the pathological model Monanema martini and in 8, upon 9, species of Cercopithifilaria. (iii) Supergroup F Wolbachia is identified in two newly screened Mansonella species and in Cercopithifilaria japonica. (iv) Type F Wolbachia infect the intestinal cells and somatic female genital tract. (v) Among Oswaldofilariinae, Waltonellinae and Splendidofilariinae, from saurian, anuran and bird respectively, Wolbachia are not detected.
  
  
  CONCLUSIONS
  The absence of Wolbachia in 63% of onchocercids, notably in the ancestral Oswaldofilariinae estimated 140 mya old, the diverse tissues or specimens distribution, and a recent lateral transfer in supergroup F Wolbachia, modify the current view on the role and evolution of the endosymbiont and their hosts. Further genomic analyses on some of the newly sampled species are welcomed to decipher the open questions.
authors: Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano Bicocca, Milano, Italy.
authors: Emanuele
authors: E
authors: Ferri
authors: Odile
authors: O
authors: Bain
authors: Michela
authors: M
authors: Barbuto
authors: Coralie
authors: C
authors: Martin
authors: Nathan
authors: N
authors: Lo
authors: Shigehiko
authors: S
authors: Uni
authors: Frederic
authors: F
authors: Landmann
authors: Sara G
authors: SG
authors: Baccei
authors: Ricardo
authors: R
authors: Guerrero
authors: Sueli
authors: S
authors: de Souza Lima
authors: Claudio
authors: C
authors: Bandi
authors: Samuel
authors: S
authors: Wanji
authors: Moustapha
authors: M
authors: Diagne
authors: Maurizio
authors: M
authors: Casiraghi
mesh_terms: D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D004275:DNA, Ribosomal / Q000235:genetics; D005260:Female; D005370:Filarioidea / Q000166:cytology / Q000302:isolation & purification* / Q000382:microbiology*; D005453:Fluorescence; D016905:Gram-Negative Bacterial Infections / Q000235:genetics* / Q000382:microbiology*; D058507:Host Specificity; D054884:Host-Pathogen Interactions; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D011419:Propidium / Q000378:metabolism; D013045:Species Specificity; D020577:Wolbachia / Q000166:cytology / Q000235:genetics / Q000502:physiology*
chemical_list: D004275:DNA, Ribosomal; D011419:Propidium