A quantitative model of nitrogen fixation in the presence of ammonium - Fig 3

Simulated protein specific rates of (A) nitrogen fixation (B) respiration and (C) concentrations of protein in continuous cultures of Azotobacter vinelandii. The simulations (solid curves) are compared to laboratory data (points) redrawn from [34,41]. Different colors represent different O2 concentration in the culture (see the legend in upper right). Here 100% O2 equals 225 μM thus approximately O2 saturation under normal air composition at 30°C. At lower to medium C/N in (B) and (C), model results show same values for various O2 concentrations. In (A), “+” are data based on acetylene reduction, and “×” are based on the rate of total nitrogen incorporation. The right y-axis in (A) shows the model predicted ratio of nitrogen fixation relative to total nitrogen incorporated into biomass. In both the simulation and the laboratory data, the dilution rate was constant (0.15 h-1), and C/N ratio is based on the constant ammonium resource of 2.5 mol m-3.