FIGURE 4.

Growth of WT and nirBD narB S. meliloti strains. WT (●) or nirBD narB (▲) strain were grown to exponential phase (OD₆₀₀= 0.2–0.3) in Vincent Minimal Medium (VMM) containing either glutamate (red lines) or NH₄Cl (black lines) as the sole nitrogen source. At time zero, cells grown in VMM with glutamate or NH₄Cl were collected, centrifuged, washed once by centrifugation, and resuspended at the same OD₆₀₀ in VMM containing only KNO₃ (dotted line), or a combination of KNO₃ and glutamate (red solid line) or NH₄Cl (black solid line). OD₆₀₀ was measured over a 24 h period. A representative experiment is shown on the figure.