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  • 1
    Publication Date: 2013-08-21
    Description: Mammals harbour a complex gut microbiome, comprising bacteria that confer immunological, metabolic and neurological benefits. Despite advances in sequence-based microbial profiling and myriad studies defining microbiome composition during health and disease, little is known about the molecular processes used by symbiotic bacteria to stably colonize the gastrointestinal tract. We sought to define how mammals assemble and maintain the Bacteroides, one of the most numerically prominent genera of the human microbiome. Here we find that, whereas the gut normally contains hundreds of bacterial species, germ-free mice mono-associated with a single Bacteroides species are resistant to colonization by the same, but not different, species. To identify bacterial mechanisms for species-specific saturable colonization, we devised an in vivo genetic screen and discovered a unique class of polysaccharide utilization loci that is conserved among intestinal Bacteroides. We named this genetic locus the commensal colonization factors (ccf). Deletion of the ccf genes in the model symbiont, Bacteroides fragilis, results in colonization defects in mice and reduced horizontal transmission. The ccf genes of B. fragilis are upregulated during gut colonization, preferentially at the colonic surface. When we visualize microbial biogeography within the colon, B. fragilis penetrates the colonic mucus and resides deep within crypt channels, whereas ccf mutants are defective in crypt association. Notably, the CCF system is required for B. fragilis colonization following microbiome disruption with Citrobacter rodentium infection or antibiotic treatment, suggesting that the niche within colonic crypts represents a reservoir for bacteria to maintain long-term colonization. These findings reveal that intestinal Bacteroides have evolved species-specific physical interactions with the host that mediate stable and resilient gut colonization, and the CCF system represents a novel molecular mechanism for symbiosis.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3893107/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3893107/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lee, S Melanie -- Donaldson, Gregory P -- Mikulski, Zbigniew -- Boyajian, Silva -- Ley, Klaus -- Mazmanian, Sarkis K -- DK078938/DK/NIDDK NIH HHS/ -- GM007616/GM/NIGMS NIH HHS/ -- GM099535/GM/NIGMS NIH HHS/ -- P01 DK091222/DK/NIDDK NIH HHS/ -- R01 DK078938/DK/NIDDK NIH HHS/ -- R01 GM099535/GM/NIGMS NIH HHS/ -- R21 DK083633/DK/NIDDK NIH HHS/ -- England -- Nature. 2013 Sep 19;501(7467):426-9. doi: 10.1038/nature12447. Epub 2013 Aug 18.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, California 91125, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23955152" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Bacterial Proteins/genetics/metabolism ; Bacteroides/*classification/genetics/growth & development/*physiology ; Bacteroides fragilis/genetics/growth & development/metabolism ; Colon/microbiology ; Conserved Sequence/genetics ; Evolution, Molecular ; Female ; Gastrointestinal Tract/*microbiology ; Gene Deletion ; Genes, Bacterial/genetics ; Germ-Free Life ; Intestinal Mucosa/microbiology ; Male ; Metagenome/*physiology ; Mice ; Polysaccharides/metabolism ; Species Specificity ; Symbiosis/genetics
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2011-04-23
    Description: Mucosal surfaces constantly encounter microbes. Toll-like receptors (TLRs) mediate recognition of microbial patterns to eliminate pathogens. By contrast, we demonstrate that the prominent gut commensal Bacteroides fragilis activates the TLR pathway to establish host-microbial symbiosis. TLR2 on CD4(+) T cells is required for B. fragilis colonization of a unique mucosal niche in mice during homeostasis. A symbiosis factor (PSA, polysaccharide A) of B. fragilis signals through TLR2 directly on Foxp3(+) regulatory T cells to promote immunologic tolerance. B. fragilis lacking PSA is unable to restrain T helper 17 cell responses and is defective in niche-specific mucosal colonization. Therefore, commensal bacteria exploit the TLR pathway to actively suppress immunity. We propose that the immune system can discriminate between pathogens and the microbiota through recognition of symbiotic bacterial molecules in a process that engenders commensal colonization.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3164325/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3164325/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Round, June L -- Lee, S Melanie -- Li, Jennifer -- Tran, Gloria -- Jabri, Bana -- Chatila, Talal A -- Mazmanian, Sarkis K -- AI 080002/AI/NIAID NIH HHS/ -- AI 088626/AI/NIAID NIH HHS/ -- DK 078938/DK/NIDDK NIH HHS/ -- DK 083633/DK/NIDDK NIH HHS/ -- R01 AI085090/AI/NIAID NIH HHS/ -- R01 AI085090-01/AI/NIAID NIH HHS/ -- R01 AI085090-01S1/AI/NIAID NIH HHS/ -- R01 AI085090-02/AI/NIAID NIH HHS/ -- R01 AI085090-03/AI/NIAID NIH HHS/ -- R01 DK078938/DK/NIDDK NIH HHS/ -- R01 DK078938-01A2/DK/NIDDK NIH HHS/ -- R01 DK078938-02/DK/NIDDK NIH HHS/ -- R01 DK078938-03/DK/NIDDK NIH HHS/ -- R01 DK078938-04/DK/NIDDK NIH HHS/ -- R21 AI080002/AI/NIAID NIH HHS/ -- R21 AI080002-01/AI/NIAID NIH HHS/ -- R21 AI080002-02/AI/NIAID NIH HHS/ -- R21 AI088626/AI/NIAID NIH HHS/ -- R21 AI088626-01/AI/NIAID NIH HHS/ -- R21 AI088626-02/AI/NIAID NIH HHS/ -- R21 DK083633/DK/NIDDK NIH HHS/ -- R21 DK083633-01A1/DK/NIDDK NIH HHS/ -- R21 DK083633-02/DK/NIDDK NIH HHS/ -- New York, N.Y. -- Science. 2011 May 20;332(6032):974-7. doi: 10.1126/science.1206095. Epub 2011 Apr 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Division of Biology, California Institute of Technology, Pasadena, CA 91125, USA. jround@caltech.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/21512004" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Bacteroides fragilis/*growth & development/*immunology ; Colon/immunology/microbiology ; Germ-Free Life ; Homeostasis ; Humans ; *Immune Tolerance ; Immunity, Mucosal ; Interleukin-10/metabolism ; Intestinal Mucosa/*immunology/*microbiology ; Metagenome ; Mice ; Mice, Inbred C57BL ; Models, Biological ; Polysaccharides, Bacterial/immunology/*metabolism ; Signal Transduction ; Specific Pathogen-Free Organisms ; Symbiosis ; T-Lymphocytes, Regulatory/immunology ; Th17 Cells/immunology ; Toll-Like Receptor 2/immunology/*metabolism
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
    ISSN: 1434-601X
    Keywords: 25.85.Ge ; 25.70.Jj ; 25.70.Gh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We examine what information can be obtained from fission angular distributions through precise measurements and an analysis in terms of the simple statistical model of Ericson. We report on the systematics of the decoupling angle and present the role of the angular momentum coupling between the entrance and the exit channel. The results indicate that the directional coupling of the angular momentum in the entrance and the exit channel is always strong for heavy-ion induced fission, and the angular momentum coupling plays a decisive role on the angular distribution of fission fragments. The average channel spins of fission fragments 〈If〉 are deduced through the decoupling angles determined experimentally. They agree well with γ-multiplicity measurements.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-601X
    Keywords: 25.70.Jj ; 25.70.Lm ; 25.85.Ge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The binary decay properties of the47V nucleus, produced in the35Cl +12C reaction, have been investigated at the35Cl bombarding energiesE lab = 180 and 200 MeV by means of a kinematical coincidence technique. Binary reaction products show full energy equilibration and a characteristic 1/sin(θ cm) angular distribution. The elemental distribution of the fully-damped products is asymmetric, similar to what has previously been observed in the decay of the56Ni nucleus. Comparison with theoretical model predictions suggests the occurrence of a fusion-fission rather than orbiting process. Moreover the calculations performed using the Extended Hauser-Feshbach Method reproduce well the experimental fission yields. A general discussion of orbiting and fusionfission experimental data of light heavy-ion systems is presented in the framework of the calculated number of available open channels for these systems.
    Type of Medium: Electronic Resource
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