Characterization of a mazEF Toxin-Antitoxin Homologue from Staphylococcus equorum

Toxin-antitoxin (TA) systems encoded in prokaryotic genomes fall into five types, typically composed of two distinct small molecules, an endotoxic protein and a cis-encoded antitoxin of ribonucleic or proteinaceous nature. In silico analysis revealed seven putative type I and three putative type II TA systems in the genome of the nonpathogenic species strain Staphylococcus equorum SE3. Among these, a MazEF system orthologue termed MazEFseq was further characterized. 5′ rapid amplification of cDNA ends (RACE) revealed the expression and the transcriptional start site of mazEseq, indicating an immediately upstream promoter. Heterologous expression of the putative toxin-encoding mazFseq gene imposed growth cessation but not cell death on Escherichia coli. In vivo and in vitro, MazFseq was shown to cleave at UACAU motifs, which are remarkably abundant in a number of putative metabolic and regulatory S. equorum gene transcripts. Specific interaction between MazFseq and the putative cognate antitoxin MazEseq was demonstrated by bacterial two-hybrid analyses. These data strongly suggest that MazEFseq represents the first characterized TA system in a nonpathogenic Staphylococcus species and indicate that MazEF modules in staphylococci may also control processes beyond pathogenicity.