Figure 5.

Phylogenetic location and genetic origin of spa from GAS strains by comparison with other Streptococcus species. (A) The phylogenetic construction shows that the Spa protein in GAS strains is phylogenetically close to the M-proteins Szm from S. equi subsp. zooepidemicus and Sem from S. equi subsp. equi. The phylogenetic topology was constructed based on the C-terminal conserved sequences of Spa using maximum-likelihood method with 1000 bootstraps. The following synonyms for species names are used: Szoo for Streptococcus equi subsp. zooepidemicus, Sequi for Streptococcus equi subsp. equi and Spyo for Streptococcus pyogenes. The synonyms for strain names are also used: M18–8232 for M18 MGAS8232, M71-NS53 for M71 NS53, M53-AP53 for M53 AP53, M6–10394 for M6 MGAS10394, M1-SF370 for M1 SF370, and M12–9429 for M12 MGAS9429. Most GAS strains cluster in one single branch, including NS53. Two GAS strains M18 MGAS8232 and M36 ss873 cluster in a separate branch with S. equi. (B) The gene organization and break-point identification show that spa and its flanking sequences of length ∼ 5 kb from M18 MGAS8232 may have been acquired from donors of S. equi via gene conversion by replacing a fragment of length ∼ 2.9 kb containing the gene encoding the collagen-binding protein SclA. The double arrows indicate the break points, where the replacement may have occurred. (C) The spa and its flanking sequences of length ∼ 5.9 kb in NS53 may have been inserted between the gene nusG and nga probably via a transposon element IS1562 downstream spa.