title: The lifestyle of the segmented filamentous bacterium: a non-culturable gut-associated immunostimulating microbe inferred by whole-genome sequencing.
abstract: Numerous microbes inhabit the mammalian intestinal track and strongly impact host physiology; however, our understanding of this ecosystem remains limited owing to the high complexity of the microbial community and the presence of numerous non-culturable microbes. Segmented filamentous bacteria (SFBs), which are clostridia-related Gram-positive bacteria, are among such non-culturable populations and are well known for their unique morphology and tight attachment to intestinal epithelial cells. Recent studies have revealed that SFBs play crucial roles in the post-natal maturation of gut immune function, especially the induction of Th17 lymphocytes. Here, we report the complete genome sequence of mouse SFBs. The genome, which comprises a single circular chromosome of 1 620 005 bp, lacks genes for the biosynthesis of almost all amino acids, vitamins/cofactors and nucleotides, but contains a full set of genes for sporulation/germination and, unexpectedly, for chemotaxis/flagella-based motility. These findings suggest a triphasic lifestyle of the SFB, which comprises two types of vegetative (swimming and epicellular parasitic) phases and a dormant (spore) phase. Furthermore, SFBs encode four types of flagellin, three of which are recognized by Toll-like receptor 5 and could elicit the innate immune response. Our results reveal the non-culturability, lifestyle and immunostimulation mechanisms of SFBs and provide a genetic basis for the future development of the SFB cultivation and gene-manipulation techniques.
authors.affiliation: Department of Microbiology, Kagawa University, Miki-cho, Kita-gun, Kagawa, Japan.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Kuwahara
authors.forename: Yositoshi
authors.initials: Y
authors.lastname: Ogura
authors.forename: Kenshiro
authors.initials: K
authors.lastname: Oshima
authors.forename: Ken
authors.initials: K
authors.lastname: Kurokawa
authors.forename: Tadasuke
authors.initials: T
authors.lastname: Ooka
authors.forename: Hideki
authors.initials: H
authors.lastname: Hirakawa
authors.forename: Takehiko
authors.initials: T
authors.lastname: Itoh
authors.forename: Haruyuki
authors.initials: H
authors.lastname: Nakayama-Imaohji
authors.forename: Minoru
authors.initials: M
authors.lastname: Ichimura
authors.forename: Kikuji
authors.initials: K
authors.lastname: Itoh
authors.forename: Chieko
authors.initials: C
authors.lastname: Ishifune
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Maekawa
authors.forename: Koji
authors.initials: K
authors.lastname: Yasutomo
authors.forename: Masahira
authors.initials: M
authors.lastname: Hattori
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hayashi
mesh_terms: D000818:Animals; D001419:Bacteria / Q000235:genetics* / Q000276:immunology / Q000378:metabolism / Q000648:ultrastructure; D053898:Biosynthetic Pathways / Q000235:genetics; D002633:Chemotaxis; D002876:Chromosomes, Bacterial / Q000235:genetics; D005407:Flagella / Q000378:metabolism; D005408:Flagellin / Q000276:immunology / Q000378:metabolism; D023061:Gene Order; D016680:Genome, Bacterial / Q000235:genetics*; D006801:Humans; D007422:Intestines / Q000382:microbiology*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D013170:Spores
chemical_list: D005408:Flagellin