Genetic basis for lipopolysaccharide O-antigen biosynthesis in bordetellae

Bordetella bronchiseptica and Bordetella parapertussis express a surface po lysaccharide, attached to a lipopolysaccharide, which has been called O ant igen. This structure is absent from Bordetella pertussis. We report the ide ntification of a large genetic locus in B. bronchiseptica and B. parapertus sis that is required for O-antigen biosynthesis. The locus is replaced by a n insertion sequence in B. pertussis, explaining the lack of O-antigen bios ynthesis in this species. The DNA sequence of the B. bronchiseptica locus h as been determined and the presence of 21 open reading frames has been reve aled. We have ascribed putative functions to many of these open reading fra mes based on database searches. Mutations in the locus in B. bronchiseptica and B. parapertussis prevent O-antigen biosynthesis and provide tools for the study of the role of O antigen in infections caused by these bacteria.