SarA is an essential positive regulator of Staphylococcus epidermidis biofilm development

Staphylococcus epidermidis biofilm formation is associated with the production of the polysaccharide intercellular adhesin (PIA)--poly-N-acetylglucosamine polysaccharide (PNAG) by the products of the icaADBC operon. Recent evidence indicates that SarA, a central regulatory element that controls the production of Staphylococcus aureus virulence factors, is essential for the synthesis of PIA/PNAG and the ensuing biofilm development in this species. Based on the presence of a sarA homolog, we hypothesized that SarA could also be involved in the regulation of the biofilm formation process in S. epidermidis. To investigate this, we constructed nonpolar sarA deletions in two genetically unrelated S. epidermidis clinical strains, O-47 and CH845. The SarA mutants were completely defective in biofilm formation, both in the steady-state conditions of a microtiter dish assay and in the flow conditions of microfermentors. Reverse transcription-PCR experiments showed that the mutation in the sarA gene resulted in downregulation of the icaADBC operon transcription in an IcaR-independent manner. Purified SarA protein showed high-affinity binding to the icaA promoter region by electrophoretic mobility shift assays. Consequently, mutation in sarA provoked a significant decrease in the amount of PIA/PNAG on the cell surface. Furthermore, heterologous complementation of S. aureus sarA mutants with the sarA gene of S. epidermidis completely restored biofilm formation. In summary, SarA appeared to be a positive regulator of transcription of the ica locus, and in its absence, PIA/PNAG production and biofilm formation were diminished. Additionally, we present experimental evidence showing that SarA may be an important regulatory element that controls S. epidermidis virulence factors other than biofilm formation.