title: Polymorphism, genetic exchange and intragenic recombination of the aureolysin gene among Staphylococcus aureus strains.
abstract: BACKGROUND
  Staphylococcus aureus expresses several proteases, which are thought to contribute to the virulence of this bacterium. Here we focus on aureolysin, the major thermolysin-like metalloprotease. Despite the importance of aureolysin in the physiology and pathogenesis of S. aureus, relatively little information was so far available concerning the aur gene diversity and mobility within and between the major subdivisions of the S. aureus population. Therefore, an epidemiologically and genetically diverse collection of S. aureus strains was used to determine the range of aureolysin (aur) gene polymorphism.
  
  
  RESULTS
  Sequence analyses support the conclusion that the aur gene occurs in two distinct types of related sequences. The aur gene was much more polymorphic but, at the same time, showed higher purifying selection than genes utilized for multilocus sequence typing (MLST). Gene trees constructed from aur and concatenated MLST genes revealed several putative assortative recombination events (i.e. entire aur gene exchanges) between divergent lineages of S. aureus. Evidence for intragenic recombination events (i.e. exchanges of internal aur segments) across aur genes was also found. The biochemical properties and substrate specificity of the two types of aureolysin purified to homogeneity were studied, revealing minor differences in their affinity to low molecular weight synthetic substrates.
  
  
  CONCLUSIONS
  Although numerous nucleotide differences were identified between the aur alleles studied, our findings showed that a strong purifying selection is acting on the aur gene. Moreover, our study distinguishes between homologous exchanges of the entire aur gene (assortative recombination) between divergent S. aureus lineages and recombination events within aur genes.
authors.affiliation: National Medicines Institute, 00-725 Warsaw, Poland. artur_sabat@yahoo.com
authors.forename: Artur J
authors.initials: AJ
authors.lastname: Sabat
authors.forename: Benedykt
authors.initials: B
authors.lastname: Wladyka
authors.forename: Klaudia
authors.initials: K
authors.lastname: Kosowska-Shick
authors.forename: Hajo
authors.initials: H
authors.lastname: Grundmann
authors.forename: Jan Maarten
authors.initials: JM
authors.lastname: van Dijl
authors.forename: Julia
authors.initials: J
authors.lastname: Kowal
authors.forename: Peter C
authors.initials: PC
authors.lastname: Appelbaum
authors.forename: Adam
authors.initials: A
authors.lastname: Dubin
authors.forename: Waleria
authors.initials: W
authors.lastname: Hryniewicz
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D015373:Bacterial Typing Techniques; D019143:Evolution, Molecular; D005798:Genes, Bacterial; D008666:Metalloendopeptidases / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D010802:Phylogeny; D011110:Polymorphism, Genetic; D011995:Recombination, Genetic; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D013211:Staphylococcus aureus / Q000145:classification / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; D008666:Metalloendopeptidases; C115504:aureolysin