Acid and base stress and transcriptomic responses in Bacillus subtilis

Area of Science:

• Microbiology
• Environmental Science
• Molecular Biology

Background:

• Bacillus subtilis exhibits varying responses to environmental pH shifts.
• Adaptation to moderate acid or base conditions can enhance survival in more extreme environments.

Purpose of the Study:

• To investigate the environmental stress responses of Bacillus subtilis to acid and base conditions.
• To analyze gene expression changes in B. subtilis under different pH levels.

Main Methods:

• Bacterial cultures were subjected to pH shifts (pH 8.5 to 6.0 and 6.0 to 8.5).
• Survival rates were assessed at extreme pH values (4.5 and 10).
• Gene expression profiling was performed using Affymetrix chip hybridization for 4,095 protein-encoding open reading frames at pH 6, 7, and 9.

Main Results:

• Rapid growth recovery occurred when shifting from pH 8.5 to 6.0, but a long lag time was observed for the reverse shift.
• Cells grown at pH 6.0 showed high survival at pH 4.5, while cells grown at pH 9.0 showed high survival at pH 10.
• Growth at pH 6 upregulated genes involved in acetoin production, dehydrogenases, decarboxylases, malate metabolism, metal export, and oxidative stress.
• Growth at pH 9 upregulated genes related to arginine catabolism, glutamate synthase, polyamine transport, K(+)/H(+) antiporter, and cytochrome oxidoreductases.
• Greater genetic adaptation was observed at pH 9 compared to pH 6.

Conclusions:

• Bacillus subtilis demonstrates significant adaptation to both acidic and alkaline environments.
• The observed lag time in shifting to high pH is likely due to greater genetic adaptation required at alkaline conditions.
• Acidic pH favors pathways that consume acids and produce bases, while alkaline pH favors acid-generating catabolism.