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Different foreign genes incidentally integrated into the same locus of the Streptococcus suis genome

Tsutomu Sekizaki1, Daisuke Takamatsu, Makoto Osaki

  • 1Molecular Bacteriology Section, National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan. sekizaki@affrc.go.jp

Journal of Bacteriology
|January 22, 2005
PubMed

Insights

Foreign DNA, including restriction-modification (RM) genes, is inserted into the Streptococcus suis genome via illegitimate recombination at the purHD locus. Diverse genetic elements were found, suggesting multiple acquisition events.

Area of Science:

  • Microbiology
  • Genetics
  • Molecular Biology

Background:

  • Some Streptococcus suis strains contain type II restriction-modification (RM) systems.
  • These RM genes are hypothesized to integrate into the bacterial genome between the purH and purD genes via illegitimate recombination.

Purpose of the Study:

  • To investigate the genetic makeup of the purHD locus in 28 Streptococcus suis serotype reference strains.
  • To characterize the foreign genetic elements present in this locus and understand their integration mechanisms.

Main Methods:

  • DNA sequencing of the purHD locus from 28 S. suis reference strains.
  • Bioinformatic analysis of identified genetic regions, including G+C content analysis.
  • Experimental integration of RM genes using a thermosensitive suicide plasmid.

Main Results:

  • Four strains contained RM genes in the purHD locus.
  • Eleven strains possessed other foreign genetic regions of seven distinct classes, some containing unknown or hypothetical genes.
  • These foreign regions exhibited atypical G+C content, suggesting foreign origin.
  • Integration of foreign DNA occurred via illegitimate recombination, mediated by short nucleotide sequence identity (2-10 bp).
  • Experimental integration of RM genes did not target the purHD locus but occurred at various chromosomal sites.

Conclusions:

  • The purHD locus in Streptococcus suis is a hotspot for the integration of diverse foreign genetic elements.
  • Illegitimate recombination, driven by short sequence homology, is the primary mechanism for acquiring these foreign genes.
  • The integration appears to be incidental, with various foreign DNA types accumulating in the same genomic location.

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