has acquired sequences within the capsule locus by horizontal genetic transfer.

Expression of a capsule from one of serogroups A, B, C, W, X or Y is usually required for ( ) to cause invasive meningococcal disease. The capsule is encoded by the capsule locus, , which is proposed to have been acquired by a formerly capsule null organism by horizontal genetic transfer (HGT) from another species. Following identification of putative capsule genes in non-pathogenic species, this hypothesis is re-examined. Whole genome sequence data from species, including genomes from a diverse range of clonal complexes and capsule genogroups, and non- species, were obtained from PubMLST and GenBank. Sequence alignments of genes from the meningococcal , and predicted orthologues in other species, were analysed using Neighbor-nets, BOOTSCANing and maximum likelihood phylogenies. The meningococcal was highly mosaic within regions B, C and D. A subset of sequences within regions B and C were phylogenetically nested within homologous sequences belonging to , consistent with HGT event in which was the donor. In the of 23/39 isolates, the two copies of region D were highly divergent, with sequences being more closely related to predicted orthologues in the proposed species (GenBank accession number CP023429.1) than the same genes in isolates lacking a capsule. There was also evidence of mosaicism in the sequences of the remaining 16 isolates, as well as from many isolates. Data are consistent with the acquisition of in meningococci from , followed by further recombination events with other species. Nevertheless, the data cannot refute an alternative model, in which native meningococcal capsule existed prior to undergoing HGT with and other species. Within-genus recombination events may have given rise to the diversity of meningococcal capsule serogroups.