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Analysis of a capsular polysaccharide biosynthesis locus of Bacteroides fragilis
L E Comstock1, M J Coyne, A O Tzianabos
1Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA. lcomstock@channing.harvard.edu
Abstract:
A major clinical manifestation of infection with Bacteroides fragilis is the formation of intra-abdominal abscesses, which are induced by the capsular polysaccharides of this organism. Transposon mutagenesis was used to locate genes involved in the synthesis of capsular polysaccharides. A 24,454-bp region was sequenced and found to contain a 15,379-bp locus (designated wcf) with 16 open reading frames (ORFs) encoding products similar to those encoded by genes of other bacterial polysaccharide biosynthesis loci. Four genes encode products that are similar to enzymes involved in nucleotide sugar biosynthesis. Seven genes encode products that are similar to sugar transferases. Two gene products are similar to O-acetyltransferases, and two products are probably involved in polysaccharide transport and polymerization. The product of one ORF, WcfH, is similar to a set of deacetylases of the NodB family. Deletion mutants demonstrated that the wcf locus is necessary for the synthesis of polysaccharide B, one of the two capsular polysaccharides of B. fragilis 9343. The virulence of the polysaccharide B-deficient mutant was comparable to that of the wild type in terms of its ability to induce abscesses in a rat model of intra-abdominal infection.
Insights
Bacteroides fragilis forms abscesses using capsular polysaccharides. Researchers identified the wcf gene locus essential for polysaccharide B synthesis, but its absence did not affect abscess formation in rats, suggesting other virulence factors are involved.
Area of Science:
- Microbiology
- Molecular Biology
- Infectious Diseases
Background:
- Bacteroides fragilis is a key cause of intra-abdominal abscesses.
- Capsular polysaccharides produced by B. fragilis are critical virulence factors.
- Understanding the genetic basis of polysaccharide synthesis is crucial for developing targeted therapies.
Purpose of the Study:
- To identify genes responsible for capsular polysaccharide synthesis in Bacteroides fragilis.
- To investigate the role of specific capsular polysaccharides in the pathogenesis of intra-abdominal infections.
Main Methods:
- Transposon mutagenesis was employed to locate genes involved in capsular polysaccharide biosynthesis.
- A large genomic region (24,454 bp) was sequenced, revealing a 15,379-bp locus (wcf) with 16 open reading frames (ORFs).
- Deletion mutants were created to assess the function of the wcf locus and its encoded products, including WcfH.
Main Results:
- The wcf locus contains genes with homology to enzymes involved in nucleotide sugar biosynthesis, sugar transfer, O-acetylation, and polysaccharide transport/polymerization.
- The wcf locus was confirmed as essential for the synthesis of polysaccharide B, one of two capsular polysaccharides in B. fragilis 9343.
- A mutant deficient in polysaccharide B exhibited virulence comparable to the wild type in a rat model of intra-abdominal infection.
Conclusions:
- The wcf gene locus plays a critical role in the biosynthesis of Bacteroides fragilis capsular polysaccharide B.
- Despite the importance of polysaccharide B synthesis, its absence did not attenuate the organism's ability to induce intra-abdominal abscesses in a rat model.
- These findings suggest that other virulence factors or capsular polysaccharides may be more critical for abscess formation in this model, warranting further investigation.