Abstract
The bacterial genus Staphylococcus comprises diverse species with most being described as colonizers of human and animal skin. A relational analysis of features that discriminate its species and contribute to niche adaptation and survival remains to be fully described. In this study, an interspecies, whole-genome comparative analysis of 21 Staphylococcus species was performed based on their orthologues. Three well-defined multi-species groups were identified: group A (including aureus/epidermidis); group B (including saprophyticus/xylosus) and group C (including pseudintermedius/delphini). The machine learning algorithm Random Forest was applied to prioritize orthologs that drive formation of the Staphylococcus species groups A-C. Orthologues driving staphylococcal intrageneric diversity comprised regulatory, metabolic and antimicrobial resistance proteins. Notably, the BraSR (NsaRS) two-component system (TCS) and its associated BraDE transporters that regulate antimicrobial resistance showed limited distribution in the genus and their presence was most closely associated with a subset of Staphylococcus species dominated by those that colonize human skin. Divergence of BraSR and GraSR antimicrobial peptide survival TCS and their associated transporters was observed across the staphylococci, likely reflecting niche specific evolution of these TCS/transporters and their specificities for AMPs. Experimental evolution, with selection for resistance to the lantibiotic nisin, revealed multiple routes to resistance and differences in the selection outcomes of the BraSR-positive species S. hominis and S. aureus. Selection supported a role for GraSR in nisin survival responses of the BraSR-negative species S. saprophyticus. Our study reveals diversification of antimicrobial-sensing TCS across the staphylococci and hints at differential relationships between GraSR and BraSR in those species positive for both TCS.
Highlights
Staphylococcus Species and GenomicsThe existence of taxonomically distinct species groups was first proposed for Staphylococcus based on differential DNA–DNA hybridization methods (Kloos et al, 1991)
In contrast to the conclusions of 16S rDNA and multilocus data (Takahashi et al, 1999; Lamers et al, 2012) their analysis revealed discrete clustering of Staphylococcus species. In contrast with this analysis, no distinct clustering of S. hominis with S. haemolyticus was observed, and S. saprophyticus was assigned to the S. epidermidis group of species (Suzuki et al, 2012)
Three species pairs showed a high degree of shared orthologous clusters of genes and branched together in the cladogram: S. aureus/S. simiae, S. simulans/S. carnosus, and S. lentus/S. vitulinus
Summary
The existence of taxonomically distinct species groups was first proposed for Staphylococcus based on differential DNA–DNA hybridization methods (Kloos et al, 1991) These groups were supported by 16S rDNA sequence analysis of 38 taxa (Takahashi et al, 1999) and multilocus sequence data of around 60 species and subspecies (Lamers et al, 2012). In contrast to the conclusions of 16S rDNA and multilocus data (Takahashi et al, 1999; Lamers et al, 2012) their analysis revealed discrete clustering of Staphylococcus species. In contrast with this analysis, no distinct clustering of S. hominis with S. haemolyticus was observed, and S. saprophyticus was assigned to the S. epidermidis group of species (Suzuki et al, 2012).
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