Staphylococcus aureus Stress Response to Bicarbonate Depletion

Area of Science:

• Microbiology
• Bacterial Physiology
• Cell Wall Biology

Background:

• Bicarbonate and CO2 are vital for bacterial carboxylation.
• Staphylococcus aureus relies on the MpsABC transporter for carbon concentration.
• mpsABC deletion mutants exhibit impaired growth in ambient air.

Purpose of the Study:

• To investigate cellular and molecular changes in S. aureus under CO2/bicarbonate deficiency.
• To understand the mechanisms behind the observed resistance in the mutant strain.
• To analyze the impact of carbon limitation on S. aureus cell wall composition and gene expression.

Main Methods:

• Electron microscopy to assess cell wall thickness.
• Mass spectrometry for muropeptide analysis.
• Flow cytometry for wall teichoic acid (WTA) glycosylation profiling.
• Comparative transcriptome analysis.

Main Results:

• The ΔmpsABC mutant displayed a twofold thicker cell wall.
• Mutant cells showed resistance to lysostaphin and Triton X-100.
• Alanine incorporation into pentaglycine bridges conferred lysostaphin resistance.
• Altered WTA glycosylation (less alpha, more beta) explained Triton X-100 resistance.
• Upregulation of autolysin genes (e.g., sceD) and downregulation of cell wall-anchored proteins, secreted proteins, transporters, and toxins.

Conclusions:

• Bicarbonate deficiency acts as a stressor in S. aureus.
• This stress induces significant changes in cell wall composition.
• Global gene expression is altered, contributing to enhanced resilience.
• The study elucidates a novel stress response mechanism impacting bacterial survival.