FIG. 2.

Effects of ammonia and nitrate addition on nitrogenase activity of N₂-fixing cultures of wild-type Azoarcus sp. strain BH72 and glnB, glnK, glnBK, and amtB knockout mutants. Data are based on at least two independent experiments for all conditions tested. Arrows indicate time of ammonia or nitrate addition. (A and B) Influence of ammonium addition (2 mM NH₄Cl) on acetylene reduction (nitrogenase activity) of wild-type Azoarcus sp. strain BH72 (•), glnB (○), glnK (▪), glnBK (□), and amtB (▵) mutant strains, and glnK complementation strain BHGLKK/pKKOM (▿). (C) Effect of nitrate addition (2 mM KNO₃) on acetylene reduction (nitrogenase activity) of wild-type Azoarcus sp. strain BH72 (•) and glnB (○), glnK (▪) and glnBK (□) mutant strains.