Most non-core meningococcal genes are clustered in approximately 20 genomic islands (GIs) in a limited number of genomic regions. (a) Presence and distribution of GIs possibly acquired by horizontal transfer (see Additional data file 4 for a detailed list of genes in the GIs). (b) Novel genomic context of some minimal mobile elements (MME), regions of high plasticity occupied by different GIs in different strains. Genes of the same color encode orthologous proteins. All the genes are drawn to scale.