Mouse Segmented Filamentous Bacteria Research Articles

The Role of Segmented Filamentous Bacteria in Immune Barrier Maturation of the Small Intestine at Weaning.

The microbiological, physical, chemical, and immunological barriers of the gastrointestinal tract (GIT) begin developing in utero and finish maturing postnatally. Maturation of these barriers is essential for the proper functioning of the GIT. Maturation, particularly of the immunological barrier, involves stimulation by bacteria. Segmented filamentous bacteria (SFB) which are anaerobic, spore-forming commensals have been linked to immune activation. The presence and changes in SFB abundance have been positively correlated to immune markers (cytokines and immunoglobulins) in the rat ileum and stool samples, pre- and post-weaning. The abundance of SFB in infant stool increases from 6 months, peaks around 12 months and plateaus 25 months post-weaning. Changes in SFB abundance at these times correlate positively and negatively with the production of interleukin 17 (IL 17) and immunoglobulin A (IgA), respectively, indicating involvement in immune function and maturation. Additionally, the peak in SFB abundance when a human milk diet was complemented by solid foods hints at a diet effect. SFB genome analysis revealed enzymes involved in metabolic pathways for survival, growth and development, host mucosal attachment and substrate acquisition. This narrative review discusses the current knowledge of SFB and their suggested effects on the small intestine immune system. Referencing the published genomes of rat and mouse SFB, the use of food substrates to modulate SFB abundance is proposed while considering their effects on other microbes. Changes in the immune response caused by the interaction of food substrate with SFB may provide insight into their role in infant immunological barrier maturation.

Type 2 immunity-dependent reduction of segmented filamentous bacteria in mice infected with the helminthic parasite Nippostrongylus brasiliensis.

BackgroundDynamic interactions between the host and gastrointestinal microbiota play an important role for local and systemic immune homeostasis. Helminthic parasites modulate the host immune response, resulting in protection against autoimmune disease but also increased susceptibility to pathogen infection. The underlying mechanisms remain largely unknown.ResultsWe showed that the type 2 immune response to enteric Nippostrongylus brasiliensis infection in mice was associated with altered intestinal mucin and AMP expression and shifts in microbiota composition. Most strikingly, infection reduced concentrations of intestinal segmented filamentous bacteria (SFB), known inducers of T helper 17 cells, and IL-17-associated gene expression. Infected mice deficient in IL-13 or STAT6 did not reduce SFB or IL-17, and exogenous IL-25 replicated the effects of parasite infection in wild type mice.ConclusionsOur data show that parasite infection acts through host type 2 immunity to reduce intestinal SFB and expression of IL-17, providing an example of a microbiota-dependent immune modulation by parasites.Electronic supplementary materialThe online version of this article (doi:10.1186/s40168-015-0103-8) contains supplementary material, which is available to authorized users.

Gut Immune Maturation Depends on Colonization with a Host-Specific Microbiota

Gut microbial induction of host immune maturation exemplifies host-microbe mutualism. We colonized germ-free (GF) mice with mouse microbiota (MMb) or human microbiota (HMb) to determine whether small intestinal immune maturation depends on a coevolved host-specific microbiota. Gut bacterial numbers and phylum abundance were similar in MMb and HMb mice, but bacterial species differed, especially the Firmicutes. HMb mouse intestines had low levels of CD4(+) and CD8(+) T cells, few proliferating T cells, few dendritic cells, and low antimicrobial peptide expression--all characteristics of GF mice. Rat microbiota also failed to fully expand intestinal T cell numbers in mice. Colonizing GF or HMb mice with mouse-segmented filamentous bacteria (SFB) partially restored T cell numbers, suggesting that SFB and other MMb organisms are required for full immune maturation in mice. Importantly, MMb conferred better protection against Salmonella infection than HMb. A host-specific microbiota appears to be critical for a healthy immune system.

Single-cell sequencing provides clues about the host interactions of segmented filamentous bacteria (SFB)

Segmented filamentous bacteria (SFB) are host-specific intestinal symbionts that comprise a distinct clade within the Clostridiaceae, designated Candidatus Arthromitus. SFB display a unique life cycle within the host, involving differentiation into multiple cell types. The latter include filaments that attach intimately to intestinal epithelial cells, and from which “holdfasts” and spores develop. SFB induce a multifaceted immune response, leading to host protection from intestinal pathogens. Cultivation resistance has hindered characterization of these enigmatic bacteria. In the present study, we isolated five SFB filaments from a mouse using a microfluidic device equipped with laser tweezers, generated genome sequences from each, and compared these sequences with each other, as well as to recently published SFB genome sequences. Based on the resulting analyses, SFB appear to be dependent on the host for a variety of essential nutrients. SFB have a relatively high abundance of predicted proteins devoted to cell cycle control and to envelope biogenesis, and have a group of SFB-specific autolysins and a dynamin-like protein. Among the five filament genomes, an average of 8.6% of predicted proteins were novel, including a family of secreted SFB-specific proteins. Four ADP-ribosyltransferase (ADPRT) sequence types, and a myosin-cross-reactive antigen (MCRA) protein were discovered; we hypothesize that they are involved in modulation of host responses. The presence of polymorphisms among mouse SFB genomes suggests the evolution of distinct SFB lineages. Overall, our results reveal several aspects of SFB adaptation to the mammalian intestinal tract.

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

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.

The Lifestyle of the Segmented Filamentous Bacterium: A Non-Culturable Gut-Associated Immunostimulating Microbe Inferred by Whole-Genome Sequencing

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.

Phylogenetic Characterization of Clostridium Related Segmented Filamentous Bacteria in Mice Based on 16S Ribosomal RNA Analysis

Summary The small intestine of many animals is inhabited by non-pathogenic segmented filamentous bacteria (SFBs). SFBs are strongly attached with a holdfast to intestinal epithelial cells and to cells of Peyer's patches. In the terminal segments of SFBs, spores are formed. Previously, SFBs have been mono-associated with germ-free mice. At present, this is the only available method to obtain mono-bacterial cultures of SFBs. These symbiotic bacteria cannot be cultures in vitro , and have therefore never been characterized phylogenetically. Here, we describe for the first time the phylogenetic relationship of SFBs found in mice with other bacteria. Total DNA was extracted from SFBs, which were isolated from the ileum of these mono-associated mice. Parts of the gene coding for 16S rRNA, corresponding to positions 27 to 1100 and 27 to 1492 in E. coli 16S rRNA, were amplified by PCR using conserved rRNA-targeted oligonucleotide primers. Cloning, sequencing and successive analysis of the amplified 16S rRNA sequences showed that SFBs form a distinct group that is most closely related to Clostridium species. Oligonucleotide probes were developed and directed against parts of the V2, V6 and V9 variable regions of the SFB 16S rRNA. The specificity of these probes was confirmed by southern blot analysis of the PCR-products obtained from total SFB DNA extracts, as well as by in situ hybridization experiments, directly performed on SFB cells in the ileum of mice.

Influence of Macronutrients on Segmented Filamentous Bacteria in the Small Intestine of Mice

Segmented filamentous bacteria (SFBs) in the ileum of mice were poorly present after the feeding of milk powder as sole source of nutrition, but were abundant in animals fed on a diet based on natural ingredients. Twenty-one different purified diets were formulated so that clues could be obtained to identification of the macronutrients that may be responsible for the differential SFB promoting effects of milk powder and the natural ingredient diet. None of the purified diets induced the appearance of SFBs, suggesting that the type and amount of fat, the type ofcarbohydrate and the amount and type of fibre in the diet do not influence SFB colonisation. Alternatively, the purified diets could have lacked a substance which was present in the natural ingredient diet and is essential for SFB colonisation. Thus, although we were not able to identify nutritional factors of SFBs, it is clear that the composition of the diet is at least one factor that determines whether or not SFBs appear in the ileum of mice. Colonisation levels of SFBs in mice fed experimental diets were not associated with relative caecal weight, the percentage of fusiform-shaped bacteria in the caecum or the number of Enterobacteriaceae present in faeces. The latter three parameters were however, significantly influenced by the composition of the purified diets. Keywords: Segmented filamentous bacteria; Intestinal bacteria; Macronutrients; Mouse.