title: (Methyl)ammonium transport in the nitrogen-fixing bacterium Azospirillum brasilense.
abstract: An ammonium transporter of Azospirillum brasilense was characterized. In contrast to most previously reported putative prokaryotic NH4+ transporter genes, A. brasilense amtB is not part of an operon with glnB or glnZ which, in A. brasilense, encode nitrogen regulatory proteins PII and PZ, respectively. Sequence analysis predicts the presence of 12 transmembrane domains in the deduced AmtB protein and classifies AmtB as an integral membrane protein. Nitrogen regulates the transcription of the amtB gene in A. brasilense by the Ntr system. amtB is the first gene identified in A. brasilense whose expression is regulated by NtrC. The observation that ammonium uptake is still possible in mutants lacking the AmtB protein suggests the presence of a second NH4+ transport mechanism. Growth of amtB mutants at low ammonium concentrations is reduced compared to that of the wild type. This suggests that AmtB has a role in scavenging ammonium at low concentrations.
authors.affiliation: F. A. Janssens Laboratory of Genetics, 3001 Heverlee, Belgium.
authors.forename: A
authors.initials: A
authors.lastname: Van Dommelen
authors.forename: V
authors.initials: V
authors.lastname: Keijers
authors.forename: J
authors.initials: J
authors.lastname: Vanderleyden
authors.forename: M
authors.initials: M
authors.lastname: de Zamaroczy
mesh_terms: D015806:Azospirillum brasilense / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics*; D009584:Nitrogen / Q000378:metabolism; D010802:Phylogeny; D011401:Promoter Regions, Genetic / Q000235:genetics; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics
chemical_list: C111096:AmtB protein, E coli; D002352:Carrier Proteins; D027682:Cation Transport Proteins; D029968:Escherichia coli Proteins; D000644:Quaternary Ammonium Compounds; D011993:Recombinant Fusion Proteins; D009584:Nitrogen