Rot is a key regulator of S taphylococcus aureus biofilm formation

Abstract

Summary: S taphylococcus aureus is a significant cause of chronic biofilm infections on medical implants. We investigated the biofilm regulatory cascade and discovered that the repressor of toxins ( R ot) is part of this pathway. A USA 300 community‐associated methicillin‐resistant S . aureus strain deficient in R ot was unable to form a biofilm using multiple different assays, and we found rot mutants in other strain lineages were also biofilm deficient. By performing a global analysis of transcripts and protein production controlled by R ot, we observed that all the secreted protease genes were up‐regulated in a rot mutant, and we hypothesized that this regulation could be responsible for the biofilm phenotype. To investigate this question, we determined that R ot bound to the protease promoters, and we observed that activity levels of these enzymes, in particular the cysteine proteases, were increased in a rot mutant. By inactivating these proteases, biofilm capacity was restored to the mutant, demonstrating they are responsible for the biofilm negative phenotype. Finally, we tested the rot mutant in a mouse catheter model of biofilm infection and observed a significant reduction in biofilm burden. Thus S . aureus uses the transcription factor R ot to repress secreted protease levels in order to build a biofilm.