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

Bordetella pertussis contains two genes encoding the serospecific fimbrial subunit proteins 2 and 3 which are assembled into completed fimbriae, which elicit the formation of agglutinating antibodies. Expression of these agglutinogens can vary independently of each other. A gene library from a B. pertussis strain (fimbrial serotype 0.3) was probed with an oligonucleotide probe specific for fimbrial subunit genes. Three homologous genetic loci were identified; an active fim 3 gene, an inactive fim 2 gene and an unknown fim-homologous region. The fim 3 gene carried on a cosmid produced agglutinating fimbrial structures in B. parapertussis and in variants of B. pertussis which had lost the capacity to produce the agglutinogen. This indicated that cis-acting factors are associated with serotype variation in B. pertussis rather than the production of trans-acting repressor molecules.