Cell-Surface Phenol Soluble Modulins Regulate Staphylococcus aureus Colony Spreading

Area of Science:

• Microbiology
• Molecular Biology
• Bacterial Pathogenesis

Background:

• Staphylococcus aureus utilizes phenol-soluble modulins (PSMs) for various functions, including colony spreading.
• PSMα1-4 peptides stimulate S. aureus colony spreading, while δ-toxin (Hld, PSMγ) inhibits it.
• The precise mechanisms behind these opposing effects on colony spreading were previously unclear.

Purpose of the Study:

• To elucidate the underlying mechanisms of how PSMα1-4 and δ-toxin differentially regulate Staphylococcus aureus colony spreading.
• To investigate the roles of cell surface-associated and secreted PSMs in colony spreading.

Main Methods:

• Comparative analysis of wild-type, PSMα1-4 knockout, δ-toxin knockout, and double knockout S. aureus strains.
• Quantification of cell surface and supernatant PSM levels using various techniques.
• In vitro binding assays to assess the interaction between δ-toxin and PSMα peptides.
• Functional assays measuring S. aureus colony spreading on soft agar plates.

Main Results:

• δ-toxin knockout increased cell surface PSMα1-4 and decreased secreted PSMα1-4, indicating an interaction.
• δ-toxin inhibited the binding of PSMα2 and PSMα3 to the S. aureus cell surface in vitro.
• A double knockout strain showed reduced colony spreading, which was restored by expressing cell surface PSMα1-4 but not secreted PSMα1-4.
• Restoring δ-toxin expression did not rescue colony spreading in the double knockout strain.

Conclusions:

• Cell surface-localized PSMα1-4 are crucial for promoting Staphylococcus aureus colony spreading.
• δ-toxin suppresses colony spreading primarily by inhibiting the cell surface binding of PSMα1-4.
• This study reveals a novel regulatory mechanism controlling bacterial motility and expansion via peptide-surface interactions.