Effect of an ntrC mutation on amino acid or urea utilization and on nitrogenase switch-off in Herbaspirillum seropedicae.
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 x 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.
Gusso
Claudio L
CL
Departamento de Patologia Básica, Universidade Federal do Paraná, Curitiba, Paraná, Brasil.
de Souza
Emanuel M
EM
Rigo
Liu Un
LU
de Oliveira Pedrosa
Fábio
F
Yates
M G
MG
de M Rego
Fabiane G
FG
Klassen
Giseli
G
D000596:Amino Acids / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics*; D015536:Down-Regulation; D042803:Herbaspirillum / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D009154:Mutation; D009591:Nitrogenase / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics; D014508:Urea / Q000378:metabolism*
D000596:Amino Acids; D001426:Bacterial Proteins; C061338:NifA protein, Bacteria; D000644:Quaternary Ammonium Compounds; D014157:Transcription Factors; D014508:Urea; D009591:Nitrogenase