Phylogeny of the staphylococcal major autolysin and its use in genus and species typing

The major staphylococcal autolysin Atl is an important player in cell separation and daughter cell formation. In this study, we investigated the amino acid sequences of Atl proteins derived from 15 staphylococcal and 1 macrococcal species representatives. The overall organization of the bifunctional precursor protein consisting of the signal peptide, a propeptide (PP), the amidase (AM), six repeat sequences (R(1) to R(6)), and the glucosaminidase (GL) was highly conserved in all of the species. The most-conserved domains were the enzyme domains AM and GL; the least-conserved regions were the PP and R regions. An Atl-based phylogenetic tree for the various species representatives correlated well with the corresponding 16S rRNA-based tree and also perfectly matched the phylogenetic trees based on core genome analysis. The phylogenetic distance analysis of 18 AtlA proteins of various Staphylococcus aureus strains and 15 AtlE proteins of S. epidermidis revealed that both species representatives formed a relatively homogeneous cluster. Two S. epidermidis strains, M23864:W1 and VCU116, were identified by Atl typing that clustered far more distantly and belonged to either S. caprae and S. capitis or a new subspecies. Here we show that Atl typing is a useful tool for staphylococcal genus and species typing by using either the highly conserved AM domain or the less-conserved PP domain.