Construction and characterization of Bordetella pertussis toxin mutants

Pertussis toxin is one of the major virulence determinants produced by Bordetella pertussis. The DNA encoding the structural genes for pertussis toxin was cloned in Escherichia coli, and pertussis toxin subunit S4 was expressed under the control of the tac promoter. Mutations were introduced into the cloned toxin genes, and a conjugative shuttle vector system was devised for delivering the mutations from E. coli back into B. pertussis. The mutations were introduced by allelic exchange into the chromosome of B. pertussis resulting in a series of B. pertussis strains which were isogenic except at the loci encoding the structural genes for pertussis toxin. These B. pertussis strains were utilized to study the biogenesis of pertussis toxin. Polar mutations in the S1 gene led to a lack of detectable S2 or S4 subunits in whole-cell lysates, suggesting a polycistronic arrangement for these genes. Mutations in the S5 subunit gene resulted in a truncated S1 subunit, while mutations in the S4 gene resulted in a lack of detectable S2 subunit, suggesting that physical relationships among the toxin subunits are directly reflected in the stable biogenesis of the subunits.