A COMPARISON OF THE NUCLEOTIDE-SEQUENCES OF THE ADK AND RECA GENES OFPATHOGENIC AND COMMENSAL NEISSERIA SPECIES - EVIDENCE FOR EXTENSIVE INTERSPECIES RECOMBINATION WITHIN ADK

The sequences of the adenylate kinase gene (adk) and the RecA gene (re cA) were determined from the same isolates of Neisseria gonorrhoeae, N . meningitidis, N. lactamica, N. polysaccharea, N. cinerea, N. mucosa, N. pharyngis var. flava, N. flavescens, and N. animalis. The patterns of sequence divergence observed at adk and recA were very different. Dendrograms constructed from the recA data using two different algorit hms were statistically robust and were congruent with each other and w ith the relationships between the species previously proposed using ot her data. In contrast, the dendrograms derived from the adk data were noncongruent with each other, and with those from the recA data, and w ere statistically poorly supported. These results, along with the unif orm distribution of pairwise sequence divergences between the species at adk, suggest there has been a history of interspecies recombination within the adk gene of the human Neisseria species which has obscured the phylogenetic relationships between the species. This view was sup ported by Sawyer's runs test, and the Index of Association (I-A) betwe en codons, which provided significant evidence for interspecies recomb ination between the adk genes from the human Neisseria species, but no evidence of interspecies recombination between the recA sequences.