FIG. 6.
Effects of ammonium addition on nitrogenase activity (acetylene reduction) of N2-fixing cultures. (A) Reversible, fast, and complete inhibition (switch-off) of nitrogenase activity in Azoarcus sp. strain BH72 upon addition of 0.2 (closed circles) or 2 mM (open circles) NH4Cl (final concentration). (B) Influence of ammonium addition (2 mM) on nitrogenase activity of BH72 (wild type; open circles), BHΔfdxN(pfdxN) (complemented mutant; triangles), and BHΔfdxN (deletion mutant; closed circles). Results are from one representative of three independent experiments where similar kinetics were observed.