Fig. 3
O2 sensitivity at various concentrations of air or O2. Wild-type (open circles), FO (closed circles), and ΔfrhA mutant (closed inverted triangles) strains were cultured in formate-supplemented medium in the presence of 0, 10, 20, 30, 40% (v/v) of air (a) or 0, 4, 8, 10, 16, or 20% (v/v) of O2 (b) in the headspace. Cell densities of the wild-type strain cultured in the presence of air and O2 were 0.09 ± 0.02 and 0.09 ± 0.03, respectively, and each was set to 100%. Cell densities of the FO strain cultured in the presence of air and O2 were 0.14 ± 0.03 and 0.118 ± 0.006, respectively, and each was set to 100%. Cell density of the ΔfrhA mutant strain cultured in the presence of O2 was 0.069 ± 0.007 and was set to 100%. Cell growth was monitored by measuring the optical density at 600 nm (OD600) after 12-h cultivation. All experiments were carried out twice independently, each in triplicate