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Evolution of Bordetella pertussis and Bordetella parapertussis as Deduced from Comparative Genome Analyses, Page 1 of 2
< Previous page Next page > /docserver/preview/fulltext/10.1128/9781555815639/9781555814144_Chap33-1.gif /docserver/preview/fulltext/10.1128/9781555815639/9781555814144_Chap33-2.gifAbstract:
The genus Bordetella contains three widely studied species: Bordetella pertussis, B. parapertussis, and B. bronchiseptica. These gram-negative coccobacilli cause respiratory disease in humans and other mammals. The significance of insertion sequence (IS) elements to the evolution of B. pertussis and B. parapertussis is discussed. The bordetellae provide an opportunity to propose hypotheses to answer questions about speciation, host restriction, and differences in genotype that could account for virulence phenotypes. This was the rationale behind the Bordetella genome sequence project in which the genome sequences of representative strains of B. bronchiseptica, B. pertussis, and B. parapertussis were generated and analyzed. The evolution of any bacterium is shaped by the selection pressures faced by the organism. The evolution of species toward causing highly contagious infections, but with a low infectivity period, from a progenitor that is much less contagious but with a very prolonged infectious period is a recurrent theme in the evolution of human pathogens. A number of putative mutations are predicted to increase the level of expression of the pertussis toxin (PT) genes in B. pertussis compared to B. bronchiseptica or B. parapertussis, and this might have contributed to the change from chronic to acute infections during B. pertussis evolution. Analysis of B. parapertussis reveals that it appears to have evolved in the face of selection pressure against the expression of factors that might be recognized by existing host immunity, but in this case directed against B. pertussis.