Effect of nitrogen compounds on nitrogenase activity inHerbaspirillum seropedicaeSMR1

The effect of nitrogen compounds on growth and nitrogenase activity of Herbaspirillum seropedicae SMR1 was determined. L-Glutamate or L-glutamine as sole nitrogen sources supported growth, and nitrogenase activity was observed only after exhaustion of L-glutamate or L-glutamine from the culture medium. L-Serine, L-alanine, or ammonium chloride supported growth but not acetylene reduction activity. No growth was observed with L-histidine, L-lysine, L-arginine, or with the amines methylammonium chloride, tetramethylammonium chloride, or ethylenediamine chloride. All the compounds promoted the switch off of nitrogenase activity except L-histidine, L-lysine, or L-arginine, which were not taken up. The results showed that H. seropedicae cannot utilize exogenously added L-histidine, L-arginine, L-lysine, methylammonium chloride, tetramethylammonium chloride, or ethylediamine as the sole N source for growth. The inability of the positively charged amino acids to promote nitrogenase switch off might be a result of the lack of transport systems and the eventual further metabolism of these compounds.