Abstract
Bordetella bronchiseptica is a pathogenic bacterium causing respiratory infections in a broad range of mammals. Recently, we determined the whole genome sequence of B. bronchiseptica S798 strain isolated from a pig infected with atrophic rhinitis and found four single-nucleotide polymorphisms (SNPs) at positions -129, -72, +22, and +38 in the region upstream of dnt encoding dermonecrotic toxin (DNT), when compared with a rabbit isolate, RB50. DNT is known to be involved in turbinate atrophy observed in atrophic rhinitis. Immunoblotting, quantitative real-time PCR, and β-galactosidase reporter assay revealed that these SNPs resulted in the increased promoter activity of dnt and conferred the increased ability to produce DNT on the bacteria. Similar or identical SNPs were also found in other pig isolates kept in our laboratory, all of which produce a larger amount of DNT than RB50. Our analysis revealed that substitution of at least two of the four bases, at positions -72 and +22, influenced the promoter activity for dnt. These results imply that these SNPs are involved in the pathogenicity of bordetellae specific to pig diseases.
Highlights
Pathogenic bordetellae including Bordetella bronchiseptica, B. pertussis, and B. parapertussis are known to cause respiratory infections in mammals. These bordetellae share many virulence factors, such as filamentous hemagglutinin, adenylate cyclase toxin, dermonecrotic toxin (DNT), and type III secretion apparatus and effectors. Comparative analysis of their genome sequences revealed that B. pertussis and B. parapertussis independently evolved from a B. bronchiseptica-like ancestor [1] through genome decay including extensive loss and translocation of genes, which resulted in different host tropism: B. bronchiseptica infects various mammals, causing atrophic rhinitis in pigs, kennel cough in dogs, bronchopneumonia in guinea pigs and rabbits, and sporadic infections in humans
When compared with B. bronchiseptica RB50, a pig isolate S798 was found to contain four single-nucleotide polymorphisms (SNPs) at positions -129, -72, +22, and +38 in the region upstream of dnt, where position +1 is assigned for the transcriptional start site that was determined by the 5’-Rapid amplification of cDNA ends (RACE) method (Fig. 1A)
B. pertussis Tohama strain belonging to D1 type was found to produce as a small amount of DNT as B. bronchiseptica strains of D1 type (Fig. 1, A and B)
Summary
Pathogenic bordetellae including Bordetella bronchiseptica, B. pertussis, and B. parapertussis are known to cause respiratory infections in mammals. These bordetellae share many virulence factors, such as filamentous hemagglutinin, adenylate cyclase toxin, dermonecrotic toxin (DNT), and type III secretion apparatus and effectors. Comparative analysis of their genome sequences revealed that B. pertussis and B. parapertussis independently evolved from a B. bronchiseptica-like ancestor [1] through genome decay including extensive loss and translocation of genes, which resulted in different host tropism: B. bronchiseptica infects various mammals, causing atrophic rhinitis in pigs, kennel cough in dogs, bronchopneumonia in guinea pigs and rabbits, and sporadic infections in humans. DNT Expression of B. bronchiseptica Pig Isolates analysis, decision to publish, or preparation of the manuscript
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