Figure 3. N₂ fixation by strain SC2.

(A) Growth dynamics (OD₆₀₀) of strain SC2 in batch cultures on N-free medium (with atmospheric N₂ as sole nitrogen source). Oxygen concentrations of 1% (blue), 5% (green), 10% (red), 15% (brown) and 20% (black) were used to test their effect on N₂ fixation-mediated growth. Note that the x-axis is not in scale. (B) Effect of oxygen on the nitrogenase activity (acetylene reduction assay) in strain SC2. Ethylene production was measured after 24 hours of incubation under different concentrations of oxygen in the headspace. Data points are means ±SD of three separate experiments.