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1.
Mol Microbiol ; 53(5): 1319-30, 2004 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-15387812

RESUMO

The chromosome of Bacteroides fragilis has been shown to undergo 13 distinct DNA inversions affecting the expression of capsular polysaccharides and mediated by a serine site-specific recombinase designated Mpi. In this study, we demonstrate that members of the tyrosine site-specific recombinase family, conserved in B. fragilis, mediate additional DNA inversions of the B. fragilis genome. These DNA invertases flip promoter regions in their immediate downstream region. The genetic organization of the genes regulated by these invertible promoter regions suggests that they are operons and many of the products are predicted to be outer membrane proteins. Phenotypic analysis of a deletion mutant of one of these DNA invertases, tsr15 (aapI), which resulted in the promoter region for the downstream genes being locked ON, confirmed the synthesis of multiple surface proteins by this operon. In addition, this deletion mutant demonstrated an autoaggregative phenotype and showed significantly greater adherence than wild-type organisms in a biofilm assay, suggesting a possible functional role for these phase-variable outer surface proteins. This study demonstrates that DNA inversion is a universal mechanism used by this commensal microorganism to phase vary expression of its surface molecules and involves at least three conserved DNA invertases from two evolutionarily distinct families.


Assuntos
Proteínas de Bactérias/genética , Bacteroides fragilis/enzimologia , Bacteroides fragilis/genética , Inversão Cromossômica , Proteínas de Membrana/genética , Recombinases/metabolismo , Tirosina/metabolismo , Sequência de Aminoácidos , Animais , Cápsulas Bacterianas/química , Proteínas de Bactérias/metabolismo , Bacteroides fragilis/ultraestrutura , Sequência de Bases , DNA/genética , DNA/metabolismo , Regulação Bacteriana da Expressão Gênica , Proteínas de Membrana/metabolismo , Dados de Sequência Molecular , Óperon , Fenótipo , Polissacarídeos/genética , Polissacarídeos/metabolismo , Regiões Promotoras Genéticas , Alinhamento de Sequência
2.
Proc Natl Acad Sci U S A ; 100(18): 10446-51, 2003 Sep 02.
Artigo em Inglês | MEDLINE | ID: mdl-12915735

RESUMO

The mammalian gut represents a complex and diverse ecosystem, consisting of unique interactions between the host and microbial residents. Bacterial surfaces serve as an interface that promotes and responds to this dynamic exchange, a process essential to the biology of both symbionts. The human intestinal microorganism, Bacteroides fragilis, is able to extensively modulate its surface. Analysis of the B. fragilis genomic sequence, together with genetic conservation analyses, cross-species cloning experiments, and mutational studies, revealed that this organism utilizes an endogenous DNA inversion factor to globally modulate the expression of its surface structures. This DNA invertase is necessary for the inversion of at least 13 regions located throughout the genome, including the promoter regions for seven of the capsular polysaccharide biosynthesis loci, an accessory polysaccharide biosynthesis locus, and five other regions containing consensus promoter sequences. Bacterial DNA invertases of the serine site-specific recombinase family are typically encoded by imported elements such as phage and plasmids, and act locally on a single region of the imported element. In contrast, the conservation and unique global regulatory nature of the process in B. fragilis suggest an evolutionarily ancient mechanism for surface adaptation to the changing intestinal milieu during commensalism.


Assuntos
Cápsulas Bacterianas/biossíntese , Proteínas de Bactérias/fisiologia , Bacteroides fragilis/genética , Inversão Cromossômica , DNA Nucleotidiltransferases/fisiologia , Regiões Promotoras Genéticas , Simbiose , Sequência de Bases , Mapeamento Cromossômico , Humanos , Dados de Sequência Molecular , Fenótipo , Recombinases
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