Extensive DNA inversions in the B. fragilis genome control variable gene expression.
The obligately anaerobic bacterium Bacteroides fragilis, an opportunistic pathogen and inhabitant of the normal human colonic microbiota, exhibits considerable within-strain phase and antigenic variation of surface components. The complete genome sequence has revealed an unusual breadth (in number and in effect) of DNA inversion events that potentially control expression of many different components, including surface and secreted components, regulatory molecules, and restriction-modification proteins. Invertible promoters of two different types (12 group 1 and 11 group 2) were identified. One group has inversion crossover (fix) sites similar to the hix sites of Salmonella typhimurium. There are also four independent intergenic shufflons that potentially alter the expression and function of varied genes. The composition of the 10 different polysaccharide biosynthesis gene clusters identified (7 with associated invertible promoters) suggests a mechanism of synthesis similar to the O-antigen capsules of Escherichia coli.
Cerdeño-Tárraga
Ana M
AM
Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, UK.
Patrick
Sheila
S
Crossman
Lisa C
LC
Blakely
Garry
G
Abratt
Val
V
Lennard
Nicola
N
Poxton
Ian
I
Duerden
Brian
B
Harris
Barbara
B
Quail
Mike A
MA
Barron
Andrew
A
Clark
Louise
L
Corton
Craig
C
Doggett
Jonathan
J
Holden
Matthew T G
MT
Larke
Natasha
N
Line
Alexandra
A
Lord
Angela
A
Norbertczak
Halina
H
Ormond
Doug
D
Price
Claire
C
Rabbinowitsch
Ester
E
Woodward
John
J
Barrell
Bart
B
Parkhill
Julian
J
D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D001441:Bacteroides fragilis / Q000235:genetics* / Q000378:metabolism / Q000472:pathogenicity; D001483:Base Sequence; D007446:Chromosome Inversion; D004269:DNA, Bacterial / Q000235:genetics*; D021901:DNA, Intergenic; D015964:Gene Expression Regulation, Bacterial; D016680:Genome, Bacterial; D008969:Molecular Sequence Data; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis / Q000235:genetics; D011401:Promoter Regions, Genetic; D045522:Recombinases / Q000235:genetics; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D014158:Transcription, Genetic
D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; D021901:DNA, Intergenic; D011135:Polysaccharides, Bacterial; D045522:Recombinases