Serotype variation in Bordetella pertussis is governed by cis-acting elements

Area of Science:

• Microbiology
• Molecular Biology
• Immunology

Background:

• Bordetella pertussis possesses two genes, fim 2 and fim 3, encoding serospecific fimbrial subunit proteins.
• These proteins assemble into fimbriae that stimulate the production of agglutinating antibodies.
• Independent regulation of fim 2 and fim 3 gene expression influences serotype variation.

Purpose of the Study:

• To investigate the genetic basis of serotype variation in Bordetella pertussis.
• To identify the genetic loci responsible for fimbrial subunit protein expression.
• To determine whether cis-acting factors or trans-acting repressors mediate serotype variation.

Main Methods:

• Construction of a Bordetella pertussis gene library from a strain with fimbrial serotype 0.3.
• Screening the gene library using an oligonucleotide probe specific for fimbrial subunit genes.
• Cloning and expression of the fim 3 gene in Bordetella parapertussis and B. pertussis variants.

Main Results:

• Three homologous genetic loci were identified: an active fim 3 gene, an inactive fim 2 gene, and an unknown fim-homologous region.
• The active fim 3 gene, when carried on a cosmid, successfully produced agglutinating fimbrial structures in Bordetella parapertussis.
• Expression of the fim 3 gene also restored agglutinogen production in Bordetella pertussis variants that had lost this capacity.

Conclusions:

• Serotype variation in Bordetella pertussis is primarily associated with cis-acting factors that regulate gene expression.
• The findings suggest that trans-acting repressor molecules are not the primary mechanism driving serotype variation.
• The fim 3 gene plays a crucial role in the assembly of functional fimbriae and the expression of specific serotypes.