Hydrogen ion control of autolysin-dependent functions in Bacillus subtilis

Area of Science:

• Microbiology
• Bacterial Physiology
• Cell Wall Metabolism

Background:

• Autolysins are essential bacterial enzymes involved in cell wall remodeling.
• Bacillus subtilis cell wall turnover and autolysis are influenced by environmental pH.
• Understanding autolysin function is critical for bacterial lysis and antibiotic action.

Purpose of the Study:

• To investigate the influence of pH on Bacillus subtilis autolysin activity.
• To determine the role of N-acetyl-muramyl-L-alanine amidase in cell separation and antibiotic susceptibility.
• To characterize the relationship between pH, bacterial growth, and lysis.

Main Methods:

• Measurement of autolysin activity in Bacillus subtilis across various pH conditions.
• Assessing whole cell and cell wall autolysis in the presence of azide.
• Evaluating bacterial lysis and non-lytic killing induced by nafcillin at different pH levels.
• Observing bacterial growth rates and morphology (chain formation) at specific pH values.

Main Results:

• Autolysin activity was maximal in slightly alkaline media, with whole cell lysis peaking at pH 6 and 9, and cell wall autolysis at pH 9.
• Nafcillin-induced lysis was most pronounced at pH 7, with resistance observed below pH 6 and above pH 7.9.
• Maximal non-lytic killing by nafcillin occurred between pH 5 and 6.
• Bacterial growth was inhibited at pH 5 (with chain formation) and pH > 8.

Conclusions:

• The N-acetyl-muramyl-L-alanine amidase (amidase) is suggested to be involved in Bacillus subtilis cell separation due to its minimal activity at pH 5 and observed chain formation.
• Amidase activity is primarily responsible for cell wall turnover and susceptibility to nafcillin-induced lysis.
• pH significantly impacts Bacillus subtilis autolysis, growth, and response to antibiotics, highlighting the amidase's multifaceted role.