Sigma(B) activity depends on RsbU in Staphylococcus aureus

Area of Science:

• Microbiology
• Bacterial Genetics
• Stress Response Mechanisms

Background:

• Staphylococcus aureus NCTC8325 derivatives are natural rsbU mutants, lacking the positive regulator RsbU for the sigma(B) factor.
• The sigma(B) regulon controls crucial cellular functions including stress tolerance and virulence.
• RsbU's role in activating sigma(B) in this important laboratory strain was not fully understood.

Purpose of the Study:

• To investigate the function of RsbU in activating the alternative sigma factor sigma(B) in Staphylococcus aureus.
• To characterize the phenotypic consequences of rsbU mutations in S. aureus NCTC8325.
• To establish a reporter system for studying sigma(B) activity.

Main Methods:

• Utilized rsbU mutant strains of S. aureus NCTC8325.
• Employed reporter gene assays with firefly luciferase fused to sigma(B)-dependent promoters.
• Performed cis-complementation experiments by introducing the wild-type rsbU gene.

Main Results:

• rsbU mutants showed reduced H2O2/UV tolerance, increased alpha-hemolysin, and no Asp23 or staphyloxanthin production.
• Reporter gene assays indicated sigma(B) was largely inactive in 8325 derivatives.
• Complementation restored sigma(B) activity, heat inducibility, and wild-type phenotypes.

Conclusions:

• RsbU is indispensable for the activation and function of sigma(B) in Staphylococcus aureus laboratory strains.
• The absence of RsbU significantly impacts S. aureus stress response, virulence, and pigment production.
• The study provides a clear link between RsbU, sigma(B) activity, and key S. aureus phenotypes.