The relative contributions of recombination and mutation to the divergence of clones of Neisseria meningitidis

Multilocus sequence typing (MLST) is a recently developed nucleotide sequence-based method for the definitive assignment of isolates within bacterial populations to specific clones. MLST uses the same principles as multilocus enzyme electrophoresis and provides data that can be used to investigate aspects of the population genetics and evolution of bacterial species. We used an MLST data set consisting of the sequences of approximately 450-bp fragments from seven housekeeping loci from a large strain collection of Neisseria meningitidis to estimate the relative impact of recombination compared with point mutation in the diversification of N. meningitidis clonal complexes. 126 meningococcal isolates were assigned to 10 clonal complexes, 9 of which contained minor clonal variants. The allelic variation within each complex was classified as a recombinational exchange or a putative point mutation through a comparison of the sequences of each variant allele with that of the allele typically found in the clonal complex. The nine clonal complexes contained a total of 23 allelic variants, and analysis of the sequences of these variant alleles revealed that a single nucleotide site in a meningococcal housekeeping gene is at least 80-fold more likely to change as a result of recombination than as a result of mutation. This value is estimated to be 10-50-fold for Escherichia coli and approximately 50-fold for Streptococcus pneumoniae.