Fig. 8.—

Possible evolutionary steps leading to the present diversity of the plyA–lytA island of S. pneumoniae. It is proposed that the starting point corresponds to an island of about 10 kb that was introduced into the pneumococcal genome from an unknown source (A). Arrangements B, G, and H may arise by insertions of IS1167 (B), a prophage (G), and/or Tn916 (H), respectively. Insertion of an ≈8.6 kb fragment (mauve bar) and successive insertions/deletions (indels) are proposed to have taken place for arrangements C−F.