Deletion of mazF increases Staphylococcus aureus biofilm formation in an ica-dependent manner

Toxin-antitoxin (TA) systems are composed of a toxin that inhibits an essential cellular process (e.g. DNA replication, transcription, membrane integrity) and its cognate antitoxin that neutralizes the effect of the toxin. Staphylococcus aureus harbors two types of chromosomally encoded TA systems, namely mazEF_sa encoding a UACAU-specific mRNA interferase and two paralogous genes of yefM-yoeB_sa encoding a ribosome-dependent endoribonuclease system. However, little is known about the physiological role of MazEF_sa and YefM-YoeB_sa in S. aureus. Upon characterizing the phenotypes of single, double and triple gene deletion mutants, we found that mazF_sa deletion led to increased biofilm formation. Subsequently, transcriptional analysis revealed that expression of intercellular adhesin (ica) gene, icaADBC, increased in a mazF_sa deletion mutant. mazF_sa/icaADBC double gene deletion and genetic complementation approaches provided convincing evidence that increased biofilm formation was caused by an increase in poly_saccharide intercellular adhesin synthesized by icaADBC-encoded proteins. Furthermore, through the use of alanine substitutions at the conserved active residues of MazF_sa, our results suggested that ica-mediated biofilm formation depended on the mRNA interferase activity of MazF_sa. These findings give new insights not only into the physiological role of MazEF_sa in S. aureus, but also into the regulatory mechanism of ica-dependent biofilm formation.