Representational difference analysis identifies a strain-specific LPS biosynthesis locus in Bordetella spp.

Bordetella pertussis and B. bronchiseptica are genetically very closely related but differ significantly in their virulence properties. Using Representational Difference Analysis (RDA), 11 DNA fragments specific for B. pertussis Tohama I or B. bronchiseptica BB7865 were identified. All B. bronchiseptica BB7865-derived fragments also hybridized with chromosomal DNA from B. parapertussis but not from the B. pertussis strains Tohama I and W28, underlining the close phylogenetic relationship between B. bronchiseptica and B. parapertussis. The B. pertussis type strain BP18323 is a special case, as it contains DNA sequences characteristic for both B. pertussis and B. bronchiseptica. As demonstrated by pulsed-field gel electrophoresis, several of the BB7865-derived fragments are present on a single 30-kb XbaI fragment. Based on the sequences of putative coding regions, four of these fragments may code for proteins involved in carbohydrate metabolism or transport. In agreement with this notion, a mutant for one of these loci synthesizes a significantly altered lipopolysaccharide that lacks the O-specific side chains. The analysis of the corresponding genomic region in various Bordetella species showed that this locus is present in B. bronchiseptica and B. parapertussis but not in B. pertussis. This confirms that the RDA approach has identified a novel strain-specific LPS biosynthesis locus which accounts for the differences between the LPS structures elaborated by different Bordetella species.