Patterns of Sequence Divergence in 5′ Intergenic Spacers and Linked Coding Regions in 10 Species of Pathogenic Bacteria Reveal Distinct Recombinational Histories

Abstract

We compared the pattern of nucleotide difference in 8034 genes and in their 5′ intergenic spacers between conspecific pairs of genomes from 10 species of pathogenic bacteria. Certain genes or spacers showed much greater sequence divergence between the genotypes compared to others; such divergent regions plausibly originated by recombinational events by which a gene and/or spacers was donated from a divergent genome. Different patterns of divergence in genes and spacers identified different recombinational patterns. For example, in Chlamydophila pneumoniae, there were examples of both unusually divergent spacers and unusually divergent genes, but there were no cases in which a gene and its spacer were both unusually divergent. This pattern suggests that, in C. pneumoniae, recombination events have broken up the linkage between genes and 5′ spacers. By contrast, in Streptococcus agalactiae, there were a number of cases in which both spacer and gene were unusually divergent, indicating that a number of large-scale recombination events that included both genes and 5′ spacers have occurred; there was evidence of at least two large-scale recombination events in the genomic region including the pur genes in S. agalactiae.