Ectopic Expression of O Antigen in by a Novel Genomic Integration System.

We describe a novel genome integration system that enables the introduction of DNA fragments as large as 50 kbp into the chromosomes of recipient bacteria. This system, named BPI, comprises a bacterial artificial chromosome vector and phage-derived gene integration machinery. We introduced the locus of , which is required for O antigen biosynthesis, into the chromosome of , which intrinsically lacks O antigen, using the BPI system. After the introduction of the locus, presented an additional substance in the lipooligosaccharide fraction that was specifically recognized by the anti- antibody but not the anti- antibody, indicating that expressed O antigen corresponding to that of . O antigen-expressing was less sensitive to the bactericidal effects of serum and polymyxin B than the isogenic parental strain. In addition, an competitive infection assay showed that O antigen-expressing dominantly colonized the mouse respiratory tract over the parental strain. These results indicate that the BPI system provides a means to alter the phenotypes of bacteria by introducing large exogenous DNA fragments. Some bacterial phenotypes emerge through the cooperative functions of a number of genes residing within a large genetic locus. To transfer the phenotype of one bacterium to another, a means to introduce the large genetic locus into the recipient bacterium is needed. Therefore, we developed a novel system by combining the advantages of a bacterial artificial chromosome vector and phage-derived gene integration machinery. In this study, we succeeded for the first time in introducing a gene locus involved in O antigen biosynthesis of into the chromosome of , which intrinsically lacks O antigen, and using this system we analyzed phenotypic alterations in the resultant mutant strain of . The present results demonstrate that this system successfully accomplished the above-described purpose. We consider this system to be applicable to a number of bacteria other than .