Complete Genome Sequences of Rat and Mouse Segmented Filamentous Bacteria, a Potent Inducer of Th17 Cell Differentiation

Laboratory for MetaSystems Research, Quantitative Biology Center, RIKEN, Yokohama, Kanagawa, Japan.
Cell host & microbe (Impact Factor: 12.33). 09/2011; 10(3):273-84. DOI: 10.1016/j.chom.2011.08.007
Source: PubMed


Segmented filamentous bacteria (SFB) are noncultivable commensals inhabiting the gut of various vertebrate species and have been shown to induce Th17 cells in mice. We present the complete genome sequences of both rat and mouse SFB isolated from SFB-monocolonized hosts. The rat and mouse SFB genomes each harbor a single circular chromosome of 1.52 and 1.59 Mb encoding 1346 and 1420 protein-coding genes, respectively. The overall nucleotide identity between the two genomes is 86%, and the substitution rate was estimated to be similar to that of the free-living E. coli. SFB genomes encode typical genes for anaerobic fermentation and spore and flagella formation, but lack most of the amino acid biosynthesis enzymes, reminiscent of pathogenic Clostridia, exhibiting large dependency on the host. However, SFB lack most of the clostridial virulence-related genes. Comparative analysis with clostridial genomes suggested possible mechanisms for host responses and specific adaptations in the intestine.

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    • "Some SFBs belong to the candidate taxa known as Candidatus division Arthromitus, more recently referred to as Candidatus Savagella (Snel et al., 1995; Thompson, Mikaelyan & Brune, 2013). Phylogenetically speaking, these organisms form a discrete and distant lineage within the family Clostridiaceae, clustering within Clostridia Cluster I but divergent from other organisms within this cluster (Prakash et al., 2011). Candidatus division Arthromitus organisms are Gram-positive, spore-forming bacteria that are of long filamentous form consisting of segmented structures. "
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    • "SFB-specific proteins of unknown function may be candidates for this class of proteins. Other potential virulence factors include a fibronectin-binding protein that may mediate attachment, two collagenases and several flagellin genes that, unlike most other flagellin found in related bacterial species, are immunostimulatory and activate TLR5 on host cells [8] [21]. Yet, TLR5 signals via MyD88, pleading against a crucial role of SFBderived flagellins in the stimulation of TH17 response. "
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    • "intestinal phagocytes, induce IL-23 from CD103 + dendritic cells and are known to drive Th17 responses to enteric pathogens [88] [89] [90] [91] [92]. In addition to bacteria-associated molecules, extracellular ATP derived from the microbiota can as well activate the induction of Th17 cells [93]. "
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