Evidence for a common molecular origin of the capsule gene loci in Gram-negative bacteria expressing group II capsular polysaccharides

Capsular polysaccharides of Gram-negative bacteria contribute to a large extent to the pathogenicity of these organisms. We show here that the molecular organization of the capsule gene loci in different serogroups of Neisseria meningitidis is similar to that of Haemophilus influenzae and Escherichia coli. A common molecular origin of the mechanisms of encapsulation is indicated by strong homology of the genes involved in transport of the capsular polysaccharides to the cell surface in all these organisms. The proteins involved in capsular polysaccharide transport fit the characteristics of ABC (ATP-binding cassette) transporters. Furthermore, by sequence comparison of the sialytransferases of N. meningitidis B and E. coli K1, the capsule of which is composed of alpha 2,8-linked polyneuraminic acid, a significant degree of homology was observed, indicating that the capsular polysaccharide type itself has the same evolutionary origin in these two pathogens.