NOTES Orientations of the Bacteroides fragilis Capsular Polysaccharide Biosynthesis Locus Promoters during Symbiosis and Infection†

Orientations of the seven invertible polysaccharide biosynthesis locus promoters of Bacteroides fragilis were determined from bacteria grown in vitro, from feces of monoassociated and complex colonized mice, and from B. fragilis-induced murine abscesses. Bacteria grown in vivo have greater variability in orientation of polysac-charide locus promoters than culture-grown organisms. Intestinal Bacteroidales species are prominent members of the gut microbiota but can become opportunistic pathogens following spillage of intestinal contents into the abdominal cavity, with bacteria frequently isolated from blood and intra-abdominal abscesses (8, 16). The synthesis of a large number of capsular polysaccharides (PSs) that undergo phase variation is a relatively conserved property within intestinal Bacteroidales species (3). The model intestinal Bacteroidales species used to study PS synthesis and regulation is Bacteroides fragilis. The prototype strain NCTC9343 synthesizes eight distinct capsular polysaccharides, designated PSA to PSH (7). Previous studie