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Extensive DNA inversions in the B. fragilis genome control variable gene expression
Ana M Cerdeño-Tárraga1, Sheila Patrick, Lisa C Crossman
1Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, UK.
Science (New York, N.Y.)
|March 5, 2005
Summary
Bacteroides fragilis uses DNA inversions to vary its surface molecules, aiding its role as an opportunistic pathogen and gut microbe. This genetic flexibility allows for adaptation and immune evasion in the human colon.
Area of Science:
- Microbiology
- Genomics
- Bacterial Pathogenesis
Background:
- Bacteroides fragilis is an anaerobic bacterium found in the human gut microbiota.
- It is also an opportunistic pathogen capable of causing infections.
- B. fragilis exhibits significant variation in its surface components, contributing to its adaptability.
Purpose of the Study:
- To investigate the genetic mechanisms underlying the phase and antigenic variation of surface components in Bacteroides fragilis.
- To analyze the complete genome sequence for novel regulatory elements controlling gene expression.
Main Methods:
- Whole-genome sequencing of Bacteroides fragilis.
- Bioinformatic analysis to identify DNA inversion systems and gene clusters.
- Comparative genomics to identify similarities with other bacterial species.
Main Results:
- The genome revealed a large number of DNA inversion events controlling diverse cellular components.
- Two types of invertible promoters (12 group 1, 11 group 2) were identified, with one type sharing similarities with Salmonella typhimurium.
- Four intergenic shufflons were found, potentially regulating gene expression and function.
- Ten polysaccharide biosynthesis gene clusters were identified, seven with associated invertible promoters, suggesting O-antigen-like synthesis mechanisms.
Conclusions:
- DNA inversion is a key mechanism for extensive variation in Bacteroides fragilis.
- These inversions likely play a crucial role in the bacterium's adaptation, pathogenicity, and interaction with the host immune system.
- The identified polysaccharide synthesis pathways resemble those of Escherichia coli O-antigen capsules.
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