Figure 5. Influence of nitrogen sources on nitrogenase activities of the σ⁵⁴-, and T7-dependent nif systems.

Relative nitrogenase activity of mutant E. coli strains with (A) the σ⁵⁴-dependent nif system and (B) the T7-dependent nif system under various nitrogen conditions. Activities were measured in the presence of the different nitrogen sources indicated on the x axis. The nitrogenase activity of cells grown in medium contained 10 mM glutamate as the sole nitrogen source was considered to be 100%, and 0.2 mM IPTG was used for induction. Each experiment was repeated at least three times, and the error bars represent standard error.