Figure 6: Proposed hypothetical model of events in the capture and re-organisation of the cps island in meningococci.

(A) A hypothetical E-C-A-D-B cassette, containing a mono-functional galE1, was formed in an ancestral isolate (donor). This was recombined into a recipient strain containing a cnl locus to create the arrangement of the cps island found in modern pathogenic N. meningitidis in which the A-C-E cassette is flanked by the repetitive regions D and D’. (B) The D’-E-C-A-D cassette may undergo inversion via homologous recombination since Region D and D’ are able to form a hair-pin loop. (C) Serogroup switching involves the replacement of one serogroup synthetic cassette (eg. Serogroup C) with another (eg. Serogroup W). Multiple recombination events have been shown to occur within galE1, tex and galE2 in multiple studies (see text).