ANALYSIS OF PROTEINS ENCODED BY THE PTX AND PTL GENES OF BORDETELLA-BRONCHISEPTICA AND BORDETELLA-PARAPERTUSSIS

Bordetella pertussis is the only bacterial species which is known to p roduce pertussis toxin (PT); however, both Bordetella bronchiseptica a nd Bordetella parapertussis contain regions homologous to the ptx gene s of B. pertussis that encode the toxin subunits. After finding that s everal children with B. parapertussis infections exhibited modest anti body titers to PT, we examined the ptx genes of both B. parapertussis and B. bronchiseptica to determine whether they would encode stable, f unctional proteins even though their promoters are thought to be inact ive under the conditions that have been examined. We inserted a functi onal promoter directly upstream of the ptx-ptl region of both species and examined culture supernatants of the resulting strains for PT acti vity. Biologically active PT was found in the culture supernatants of both engineered species. The toxin encoded by the B. parapertussis ptx genes appeared more labile in culture supernatants than did toxin pro duced by either B. pertussis or the engineered strain of B. bronchisep tica. This lability might be due to the lack of a full-length S2 subun it. We also investigated the ptl genes of these species, which are nec essary for the secretion of this toxin, and found that both B. bronchi septica and B. parapertussis contain at least certain of these genes, including ptlE and ptlF. Moreover, B. bronchiseptica appeared to conta in all essential ptl genes since the introduction of a functional prom oter directly upstream of the ptx-ptl region resulted in both producti on and efficient secretion of toxin. These results indicate that despi te a number of amino acid changes in the sequences of the toxins, the toxins encoded by B. bronchiseptica and B. parapertussis are active.