EFFECT OF NITROGEN-COMPOUNDS ON NITROGENASE ACTIVITY IN HERBASPIRILLUM-SEROPEDICAE SMR1

The effect of nitrogen compounds on growth and nitrogenase activity of Herbaspirillum seropedicae SMR1 was determined. L-Glutamate or L-glut amine as sole nitrogen sources supported growth, and nitrogenase activ ity was observed only after exhaustion of L-glutamate or L-glutamine f rom the culture medium. L-Serine, L-alanine, or ammonium chloride supp orted growth but not acetylene reduction activity. No growth was obser ved with L-histidine, L-lysine, L-arginine, or with the amines methyla mmonium chloride, tetramethylammonium chloride, or ethylenediamine chl oride. All the compounds promoted the switch off of nitrogenase activi ty except L-histidine, L-lysine, or L-arginine, which were not taken u p. The results showed that H. seropedicae cannot utilize exogenously a dded L-histidine, L-arginine, L-lysine, methylammonium chloride, tetra methylammonium chloride, or ethylediamine as the sole N source for gro wth. The inability of the positively charged amino acids to promote ni trogenase switch off might be a result of the lack of transport system s and the eventual further metabolism of these compounds.