Affiliation:
1. Department of Gastroenterology, Children's Hospital, Boston, Massachusetts 02115
2. Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115
Abstract
ABSTRACT
Bacteroidales
species are the most abundant Gram-negative bacteria of the human intestinal microbiota. These bacteria evolved to synthesize numerous capsular polysaccharides (PS) that are subject to phase variation. In
Bacteroides fragilis
, PS synthesis is regulated so that only one of the eight PS biosynthesis loci is transcribed at a time in each bacterium. To determine if the bacteria evolved this unusual property to evade a host IgA response, we directly studied the human fecal ecosystem. We performed a longitudinal analysis of the abundant
Bacteroidales
species from 15 healthy adults at four intervals over a year. For this study, we used bacterial culture to perform analyses not accurate with DNA-based methods, including quantification of total viable
Bacteroidales
bacteria, strain maintenance, and IgA responses. Abundant
Bacteroidales
isolates were identified to the species level using multiplex PCR and 16S rRNA gene sequencing. Arbitrarily primed PCR was used for strain typing. IgA responses to endogenous strains carried over the year were analyzed, and the orientations of the invertible PS locus promoters from the ecosystem were quantified. Subjects consistently harbored from 5 × 10
8
to 8 × 10
10
Bacteroidales
bacteria/g of feces. Within the cohort, 20 different
Bacteroidales
species were detected at high concentrations.
Bacteroides uniformis
was the most prevalent; however, abundant
Bacteroidales
species varied between subjects. Strains could be maintained over the year within the ecosystem at high density. IgA responses were often not induced and did not correlate with the elimination of a strain or major changes in the orientations of the capsular PS locus promoters.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Immunology,Microbiology,Parasitology
Cited by
104 articles.
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