Abstract
BackgroundStaphylococcus aureus Repeat (STAR) elements are a type of interspersed intergenic direct repeat. In this study the conservation and variation in these elements was explored by bioinformatic analyses of published staphylococcal genome sequences and through sequencing of specific STAR element loci from a large set of S. aureus isolates.ResultsUsing bioinformatic analyses, we found that the STAR elements were located in different genomic loci within each staphylococcal species. There was no correlation between the number of STAR elements in each genome and the evolutionary relatedness of staphylococcal species, however higher levels of repeats were observed in both S. aureus and S. lugdunensis compared to other staphylococcal species. Unexpectedly, sequencing of the internal spacer sequences of individual repeat elements from multiple isolates showed conservation at the sequence level within deep evolutionary lineages of S. aureus. Whilst individual STAR element loci were demonstrated to expand and contract, the sequences associated with each locus were stable and distinct from one another.ConclusionsThe high degree of lineage and locus-specific conservation of these intergenic repeat regions suggests that STAR elements are maintained due to selective or molecular forces with some of these elements having an important role in cell physiology. The high prevalence in two of the more virulent staphylococcal species is indicative of a potential role for STAR elements in pathogenesis.
Highlights
Staphylococcus aureus Repeat (STAR) elements are a type of interspersed intergenic direct repeat
The available S. aureus and staphylococcal genomes were probed in silico for the presence of the degenerate STAR
We hypothesised that the abundance of STAR elements in staphylococcal species other than S. aureus would vary depending on the relatedness of that species to S. aureus, with more closely related species containing similar numbers of elements
Summary
Staphylococcus aureus Repeat (STAR) elements are a type of interspersed intergenic direct repeat. STAR elements consist of 14 bp direct repeats of the consensus sequence T(G/A/T). Full list of author information is available at the end of the article often have no clear role within the cell, prokaryotic repeat elements tend to be functionally significant [2,3]. These roles include transcriptional or translational phase variation of gene expression [4], modulation of mRNA transcript stability [5] and in the case of the well characterised
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