FIGURE 1.

Physiological parameters of NH₄⁺ run-out and diazotrophy. Ko M5a1 wild-type (black) and ΔnifLA (gray) strains were cultured for 24 h in NFDM medium supplemented with 0.5 mM NH₄Cl under micro-aerobic conditions. (A) Cell density (OD₆₀₀, filled circles) and supernatant NH₄⁺ concentration (dashed lines) were measured at 2.5 h intervals and again after 24 h. Cell growth attributable to NifLA expression and diazotrophy is represented by shaded fill (pale green). (B) Culture headspace was sampled at 2.5-h intervals (between 2.5 and 12.5 h) for detection of nitrogenase activity via the acetylene reduction assay. Acetylene was injected into the head space at t = 0 h. Activity values correspond to ethylene evolved per hour and per unit cell density at 25°C. Error bars represent SEM of three biological replicates. Acetylene reduction was not assayed at 24 h.