title: Study of the viral and microbial communities associated with Crohn's disease: a metagenomic approach.
abstract: OBJECTIVE
  This study aimed to analyze and compare the diversity and structure of the viral and microbial communities in fecal samples from a control group of healthy volunteers and from patients affected by Crohn's disease (CD).
  
  
  METHODS
  Healthy adult controls (n=8) and patients affected by ileocolic CD (n=11) were examined for the viral and microbial communities in their feces and, in one additional case, in the intestinal tissue. Using two different approaches, we compared the viral and microbial communities in several ways: by group (patients vs. controls), entity (viruses vs. bacteria), read assembly (unassembled vs. assembled reads), and methodology (our approach vs. an existing pipeline). Differences in the viral and microbial composition, and abundance between the two groups were analyzed to identify taxa that are under- or over-represented.
  
  
  RESULTS
  A lower diversity but more variability between the CD samples in both virome and microbiome was found, with a clear distinction between groups based on the microbiome. Only ≈5% of the differential viral biomarkers are more represented in the CD group (Synechococcus phage S CBS1 and Retroviridae family viruses), compared with 95% in the control group. Unrelated patterns of bacteria and bacteriophages were observed.
  
  
  CONCLUSIONS
  Our use of an extensive database is critical to retrieve more viral hits than in previous approaches. Unrelated patterns of bacteria and bacteriophages may be due to uneven representation of certain viruses in databases, among other factors. Further characterization of Retroviridae viruses in the CD group could be of interest, given their links with immunodeficiency and the immune responses. To conclude, some methodological considerations underlying the analysis of the viral community composition and abundance are discussed.
authors.affiliation: 1] Área de Genómica y Salud, Centro Superior de Investigación en Salud Pública-Fundación para el Fomento de la Investigación Sanitaria y Biomédica de la Comunidad Valenciana (CSISP-FISABIO), Valencia, Spain [2] CIBER Epidemiología y Salud Pública (CIBERESP), Madrid, Spain [3] Departamento de Genética, Cavanilles Institute on Biodiversity and Evolutionary Biology, University of València, Valencia, Spain.
authors.forename: Vicente
authors.initials: V
authors.lastname: Pérez-Brocal
authors.forename: Rodrigo
authors.initials: R
authors.lastname: García-López
authors.forename: Jorge F
authors.initials: JF
authors.lastname: Vázquez-Castellanos
authors.forename: Pilar
authors.initials: P
authors.lastname: Nos
authors.forename: Belén
authors.initials: B
authors.lastname: Beltrán
authors.forename: Amparo
authors.initials: A
authors.lastname: Latorre
authors.forename: Andrés
authors.initials: A
authors.lastname: Moya