Insights into the evolutionary relationships of lytA autolysin and ply pneumolysin-like genes in Streptococcus pneumoniae and related Streptococci

15 p.-8 fig.-1 tab.Streptococcus pneumoniae (pneumococcus) is amajor human pathogen. Themain pneumococcal autolysin LytA and the pneumolysin Ply are two of the bacterium’s most important virulence factors. The lytA- and ply-related genes are also found in other streptococci of the Mitis group (SMG). The precise characteristics of the lytA-related—but not the ply-related—genes of SMG and their prophages have been previously described. A search of the more than 400SMG genomic sequences available in public databases (ca. 300 for S. pneumoniae), showed Streptococcus pseudopneumoniae IS7493 to harbor four ply-related genes, two of which (plyA and plyB) have 98%identical nucleotides. The plyA homolog of S. pseudopneumoniae is conserved in all S. pneumoniae strains,and seems to be included in a pathogenicity island together with the lytA gene. However, only nonencapsulated S. pneumoniae strains possess a plyB gene,which is part of an integrative and conjugative element. Notably, the existence of a bacterial lytA-related gene in a genome is linked to the presence of plyA and vice versa. The present analysis also shows there are eight main types of plyA-lytA genomic islands. A possible stepwise scenario for the evolution of the plyA-lytA island in S. pneumoniae is proposed.This research was supported by grant SAF2012-39444-C01/02 from Ministerio de Economía y Competitividad (MINECO).A.J.M.-G. is the recipient of a Miguel Servet research contract funded by the Fondo de Investigación Sanitaria from the MINECO. Centro de Investigación Biomédica en Red de Enfermedades Respiratorias (CIBERES) is an initiative of ISCIII.Peer reviewe