Regions of the cloned Vibrio cholerae rfb genes needed to determine the Ogawa form of the O-antigen

The O-antigen of the lipopolysaccharides of Vibrio cholerae 01 can exist in two forms termed Inaba and Ogawa. We used a complementation system to demonstrate that the Ogawa phenotype is dominant over the Inaba phenotype. By using a set of deletions affecting the Ogawa rfb genes, we identified two regions which are needed to confer the Ogawa phenotype. In vitro mutagenesis of the cloned Ogawa rfb genes resulted in the isolation of variants with the Inaba phenotype. The results are interpreted with respect to previous studies demonstrating interconversion between the two forms of the V. cholerae O-antigen.