Indispensability of the Escherichia coli Carbonic Anhydrases YadF and CynT in Cell Proliferation at a Low CO₂ Partial Pressure

We found that a carbonic anhydrase, YadF, is essential for cell growth in the absence of another carbonic anhydrase, CynT, in Escherichia coli. However, mutant strains lacking both of them grew at high CO₂ concentrations (5%), where non-enzymatic mechanisms generate HCO₃⁻. This suggests that these carbonic anhydrases are essential because they maintain HCO₃⁻ levels at ambient CO₂ concentrations.