National Institute of Animal Health (NIAH)

Topics in Animal Health Research 2002

08. Evidence for horizontal transfer of the sly gene in Streptococcus suis


Suilysin, encoded by the sly gene, is a cholesterol-binding cytolysin of S. suis that may have a role in virulence.  However, both suilysin-productive and nonproductive strains of S. suis have been isolated from diseased pigs.  In this study we compared sequences of the sly region from a suilysin productive strain, DAT2, and a nonproductive strain, DAT1.  We found the presence of another gene, orf102, encoding a protein of unknown function, in the sly coding region of DAT1.  We then analyzed the genetic organization of the sly loci in 38 S. suis disease isolates and 28 reference strains using PCR and Southern hybridization.  The loci in six of the reference strains were rearranged.  All of the remaining strains were categorized as one of two types, i.e., DAT2 (sly) or DAT1 (orf102).  A phylogenetic tree based on 16S rRNA sequences was generated and revealed that both DAT types were present in strains with identical 16S rRNA sequences.  Interestingly, two strains, DAT1 and a DAT1-type reference strain, serotype 7 whose 16S rRNA sequences are relatively divergent, contain identical copies of orf102.  These results strongly suggest that S. suis acquired sly or orf102 from a foreign source and that these genes subsequently spread among S. suis strains by homologous recombination. (Molecular Bacteriology Section, Department of Infectious Diseases TEL +81-29-838-7743)


Takamatsu et al. (2002) J. Bacteriol. 184:2050-2057.