The cloning and characterization of a Bordetella pertussis gene encoding a putative hemolysin.

Abstract

Bordetella pertussis, the etiologic agent of whooping cough or pertussis, produces a multitude of virulence factors including a hemolysin. Virulent phase B. pertussis isolates are hemolytic, whereas avirulent isolates are not. Other investigations concerning B. pertussis adenylate cyclase toxin indicate it has hemolytic activity and is a member of the bacterial RTX toxin family. In an attempt to further characterize hemolysis by B. pertussis, a new B. pertussis gene was isolated which conferred a hemolytic phenotype on non-hemolytic E. coli. DNA sequencing of the putative B. pertussis hemolysin gene revealed it encoded a 27 kDa protein similar to HlyX, an FNR-like transcriptional regulator from Actinobacillus pleuropneumonia, which also confers hemolysis upon E. coli. No similarity to bacterial cytolysins was found. The B. pertussis transcriptional regulator-like gene and its encoded protein were named btr and BTR, respectively. BJB1, a BTR deficient B. pertussis strain was constructed. The btr::kan mutation was shown to have no effect on the production, or phenotypic modulation, of hemolysis by B. pertussis. BTR production was not regulated by the BvgA-S two component sensor-regulator. An FNR deficient E. coli, JRG1728 (Δfnr), was transformed with a btr recombinant plasmid pHLY1A. The B. pertussis btr gene complemented the FNR deficient E. coli to grow anaerobically on a non-fermentable carbon source. This suggested that BTR may function as a B. pertussis transcriptional regulator which responds to anoxic conditions.