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Published March 11, 2008 | Supplemental Material + Published
Journal Article Open

Regulation of surface architecture by symbiotic bacteria mediates host colonization

Abstract

Microbes occupy countless ecological niches in nature. Sometimes these environments may be on or within another organism, as is the case in both microbial infections and symbiosis of mammals. Unlike pathogens that establish opportunistic infections, hundreds of human commensal bacterial species establish a lifelong cohabitation with their hosts. Although many virulence factors of infectious bacteria have been described, the molecular mechanisms used during beneficial host–symbiont colonization remain almost entirely unknown. The novel identification of multiple surface polysaccharides in the important human symbiont Bacteroides fragilis raised the critical question of how these molecules contribute to commensalism. To understand the function of the bacterial capsule during symbiotic colonization of mammals, we generated B. fragilis strains deleted in the global regulator of polysaccharide expression and isolated mutants with defects in capsule expression. Surprisingly, attempts to completely eliminate capsule production are not tolerated by the microorganism, which displays growth deficits and subsequent reversion to express capsular polysaccharides. We identify an alternative pathway by which B. fragilis is able to reestablish capsule production and modulate expression of surface structures. Most importantly, mutants expressing single, defined surface polysaccharides are defective for intestinal colonization compared with bacteria expressing a complete polysaccharide repertoire. Restoring the expression of multiple capsular polysaccharides rescues the inability of mutants to compete for commensalism. These findings suggest a model whereby display of multiple capsular polysaccharides provides essential functions for bacterial colonization during host–symbiont mutualism.

Additional Information

© 2008 by the National Academy of Sciences. Edited by Rino Rappuoli, Novartis Vaccines, Siena, Italy, and approved January 10, 2008 (received for review October 4, 2007). Published online before print March 4, 2008. We are very grateful to Dr. Laurie Comstock (Brigham and Women's Hospital, Harvard Medical School, Boston) for helpful discussions and reagents throughout the entire course of this work, and we thank the members of the S.K.M. laboratory for comments on the manuscript. D.L.K. acknowledges support from the National Institutes of Health/National Institute of Allergy and Infectious Diseases. S.K.M. acknowledges support from the Searle Scholars Program and the Crohn's and Colitis Foundation of America.

Attached Files

Published - LIUpnas08.pdf

Supplemental Material - LIUpnas08fig10.pdf

Supplemental Material - LIUpnas08fig11.pdf

Supplemental Material - LIUpnas08fig12.pdf

Supplemental Material - LIUpnas08fig5.pdf

Supplemental Material - LIUpnas08fig6.pdf

Supplemental Material - LIUpnas08fig7.pdf

Supplemental Material - LIUpnas08fig8.pdf

Supplemental Material - LIUpnas08fig9.pdf

Supplemental Material - LIUpnas08supp.pdf

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Additional details

Created:
August 22, 2023
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