Phylogenetic associations of ISAa1 and IS150-like insertion sequences in Actinobacillus actinomycetemcomitans

The distribution and number of two insertion sequences (ISs), ISAa1 and an IS150-like element, in the genomes of a collection of Actinobacillus actino mycetemcomitans strains previously subjected to population genetic analysis were determined to obtain information about their stability and biological significance. The hybridization patterns revealed that these 15 elements a re widespread in the genome of A. actinomycetemcomitans strains and that th eir occurrence agrees with the overall population structure of the species. While the patterns of ISAa1 showed significant evolutionary stability, the IS150-like element showed evidence of intra-genomic variability even withi n members of the previously identified high-toxicity JP2 clone. Searching o f the available genome sequence of strain HK1651 of the JP2 clone (www.geno me.ou.edu/act.html) revealed close proximity of the IS elements to housekee ping genes, but no evidence of structural disruption of genes or integratio ns that may be presumed to influence pathogenic potential.