Genomic Localization of a T Serotype Locus to a Recombinatorial Zone Encoding Extracellular Matrix-Binding Proteins in Streptococcus pyogenes

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Abstract
Streptococcus pyogenes is an important bacterial pathogen afflicting humans. A striking feature is its extraordinary biological diversity, evident in the wide range of diseases it can cause and the antigenic heterogeneity present on its surface. The T antigens form the basis of a major serological typing scheme that is often used as an alternative or supplement to M typing. Unlike M typing, the genetic basis for T typing is poorly understood. In this report, the tee6 gene is localized to a position ≈3.3 kb downstream from prtF1 (or sfbI ), which encodes the Fn-binding protein, protein F, a key virulence factor. Comparison of this portion of the genome with those of four additional strains reveals the presence of genes encoding a collagen-binding protein (Cpa) and a second Fn-binding protein (PrtF2 or PfbpI). This chromosomal region—here designated the FCT region—is ≈11 to 16 kb in length and is flanked at both ends by long stretches of highly conserved sequence. For each of the five strains, the FCT region contains a unique combination of semiconserved loci, indicative of extensive intergenomic recombination. The data provide evidence that the highly recombinatorial FCT region of the S. pyogenes genome is under strong selection for change in response to the host environment.