pH tolerance in Bacillus: alkaliphiles versus non-alkaliphiles

Area of Science:

• Microbiology
• Biochemistry
• Molecular Biology

Background:

• Monovalent cation/proton antiporters are crucial for bacterial pH homeostasis, especially under alkaline stress.
• These antiporters facilitate the electrogenic uptake of protons (H+) in exchange for cytoplasmic cations like potassium (K+) and sodium (Na+).

Purpose of the Study:

• To systematically identify genes encoding antiporters involved in pH homeostasis in Bacillus subtilis (a neutrophile) and Bacillus firmus OF4 (an alkaliphile).
• To compare the roles and characteristics of these antiporters in different bacterial species with varying pH optima.

Main Methods:

• Comparative genomics and genetic analysis to identify antiporter genes in B. subtilis and B. firmus OF4.
• Functional characterization of identified antiporter systems.

Main Results:

• At least three distinct antiporters are involved in pH homeostasis in both B. subtilis and B. firmus OF4.
• B. firmus OF4 utilizes Na+/H+ antiport, while B. subtilis uses either Na+ or K+/H+ antiport for pH homeostasis.
• Homologous antiporter families (NhaC and Mrp/Pha) are present in both alkaliphiles and neutrophiles.
• A unique antiporter family found in B. subtilis is not yet identified in alkaliphiles.
• Constitutive and inducible antiporter components were observed.

Conclusions:

• Significant differences exist in the antiporter systems and other factors (e.g., cation re-entry, surface properties) contributing to the pH homeostasis capacity of neutrophilic and alkaliphilic bacteria.
• Understanding these antiporter mechanisms provides insights into bacterial adaptation to extreme environments.