Effect of an ntrC mutation on amino acid or urea utilization and on nitrogenase switch-off in Herbaspirillum seropedicae

• Published in: Canadian journal of microbiology Vol. 54; no. 3; pp. 235 - 239
• Main Authors: Gusso, C.L, Souza, E.M. de, Rigo, L.U, Pedrosa, F. de O, Yates, M.G, Rego, F.G. de M, Klassen, G
• Format: Journal Article
• Language: English
• Published: Ottawa, ON National Research Council of Canada 01.03.2008; NRC Research Press; Canadian Science Publishing NRC Research Press
• Subjects: amino acid metabolism; Amino acids; Amino Acids - metabolism; Ammonia; Ammonium; ammonium nitrogen; Bacteria; Bacterial proteins; Bacterial Proteins - genetics; Bacteriology; Biological and medical sciences; Down-Regulation; enzyme activity; Fundamental and applied biological sciences. Psychology; Gene mutations; Genetic transcription; Herbaspirillum - genetics; Herbaspirillum - growth & development; Herbaspirillum - metabolism; Herbaspirillum seropedicae; inhibition de la nitrogénase; Metabolism. Enzymes; Microbiology; Mutation; nitrate nitrogen; Nitrogen; Nitrogen fixation; nitrogen metabolism; Nitrogen sources; Nitrogenase; Nitrogenase - metabolism; nitrogenase switch-off; NtrC; NtrC protein; Physiological aspects; Quaternary Ammonium Compounds - metabolism; regulatory proteins; Transcription Factors - genetics; Urea; Urea - metabolism; Canada; Urea; Enzyme; Aminoacid; Nitrogenase; Herbaspirillum; Bacteria; Oxidoreductases; Mutation
• ISSN: 0008-4166; 1480-3275
• DOI: 10.1139/W07-135

Herbaspirillum seropedicae is a nitrogen-fixing bacterium that grows well with ammonium chloride or sodium nitrate as alternative single nitrogen sources but that grows more slowly with l -alanine, l -serine, l -proline, or urea. The ntrC mutant strain DCP286A was able to utilize only ammonium or urea of these nitrogen sources. The addition of 1 mmol·L -1 ammonium chloride to the nitrogen-fixing wild-type strain inhibited nitrogenase activity rapidly and completely. Urea was a less effective inhibitor; approximately 20% of nitrogenase activity remained 40 min after the addition of 1 mmol·L -1 urea. The effect of the ntrC mutation on nitrogenase inhibition (switch-off) was studied in strain DCP286A containing the constitutively expressed gene nifA of H. seropedicae. In this strain, nitrogenase inhibition by ammonium was completely abolished, but the addition of urea produced a reduction in nitrogenase activity similar to that of the wild-type strain. The results suggest that the NtrC protein is required for assimilation of nitrate and the tested amino acids by H. seropedicae. Furthermore, NtrC is also necessary for ammonium-induced switch-off of nitrogenase but is not involved in the mechanism of nitrogenase switch-off by urea.