title: Effect of an ntrC mutation on amino acid or urea utilization and on nitrogenase switch-off in Herbaspirillum seropedicae.
abstract: 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.
authors.affiliation: Departamento de Patologia Básica, Universidade Federal do Paraná, Curitiba, Paraná, Brasil.
authors.forename: Claudio L
authors.initials: CL
authors.lastname: Gusso
authors.forename: Emanuel M
authors.initials: EM
authors.lastname: de Souza
authors.forename: Liu Un
authors.initials: LU
authors.lastname: Rigo
authors.forename: Fábio
authors.initials: F
authors.lastname: de Oliveira Pedrosa
authors.forename: M G
authors.initials: MG
authors.lastname: Yates
authors.forename: Fabiane G
authors.initials: FG
authors.lastname: de M Rego
authors.forename: Giseli
authors.initials: G
authors.lastname: Klassen
mesh_terms: 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*
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; C061338:NifA protein, Bacteria; D000644:Quaternary Ammonium Compounds; D014157:Transcription Factors; D014508:Urea; D009591:Nitrogenase