Interspecies recombination and phylogenetic distortions within the glutamine synthetase and shikimate dehydrogenase genes of Neisseria meningitidisand commensal Neisseria species.

Visual inspection showed clear evidence of a history of intraspecies recombinational exchanges within the neighbouring meningococcal shikimate dehydrogenase (aroE) and glutamine synthetase (glnA) genes, which was supported by the non-congruence of the trees constructed from the sequences of these genes from different meningococcal strains, and by statistical tests for mosaic structure. Many examples were also found of highly localized interspecies recombinational exchanges between the meningococcal aroE and glnA genes and those of commensal Neisseria species. These exchanges appear to have inflated the sequence variation at these loci, and have resulted in major distortions of the phylogenetic trees constructed from the sequences of the aroE and glnA genes of human pathogenic and commensal Neisseria species. Statistical tests for sequence mosaicism, and for anomalies within the Neisseria species trees, strongly supported the view that frequent interspecies recombination has occurred within aroE and glnA. The high levels of sequence variation, and intra- and interspecies recombination, within aroE and glnA did not appear to be due to a 'hitch-hiking' effect caused by positive selection for variation at a neighbouring gene. Our results suggest that interspecies recombinational exchanges with commensal Neisseria occur frequently in some meningococcal 'housekeeping' genes as they can be observed readily even when there appears to be no obvious selection for the recombinant phenotypes.