Ammonium utilization in Bacillus subtilis: transport and regulatory functions of NrgA and NrgB.
Bacillus subtilis uses glutamine as the best source of nitrogen. In the absence of glutamine, alternative nitrogen sources such as ammonium can be used. Ammonium utilization involves the uptake of the gas or the ammonium ion, the synthesis of glutamine by the glutamine synthetase and the recycling of the glutamate by the glutamate synthase. In this work, ammonium transport in B. subtilis was studied. At high ammonium concentrations, a large fraction of the ammonium is present as ammonia, which may enter the cell via diffusion. In contrast, the ammonium transporter NrgA is required for ammonium utilization at low concentrations or at low pH values when the equilibrium between uncharged ammonia and the ammonium ion is shifted towards ammonium. Moreover, a functional NrgA is essential for the transport of the ammonium analogue methylammonium. NrgA is encoded in the nrgAB operon. The product of the second gene, NrgB, is a member of the PII family of regulatory proteins. In contrast to PII proteins from other organisms, there is no indication for a covalent modification of NrgB in response to the nitrogen supply of the cell. It is demonstrated here that NrgB is localized at the membrane, most likely in association with the ammonium transporter NrgA. The presence of a functional NrgB is required for full-level expression of the nrgAB operon in response to nitrogen limitation, suggesting that NrgB might relay the information on ammonium availability to downstream regulatory factors and thus fine-tune their activity.
Lehrstuhl für Mikrobiologie, Institut für Mikrobiologie, Biochemie und Genetik der Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 5, D-91058 Erlangen, Germany.
Christian
C
Detsch
Lehrstuhl für Mikrobiologie, Institut für Mikrobiologie, Biochemie und Genetik der Friedrich-Alexander-Universität Erlangen-Nürnberg, Staudtstr. 5, D-91058 Erlangen, Germany.
Jörg
J
Stülke
D001412:Bacillus subtilis / Q000254:growth & development / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001692:Biological Transport; D017931:DNA Primers; D005838:Genotype; D007700:Kinetics; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008744:Methylamines / Q000378:metabolism*; D051922:PII Nitrogen Regulatory Proteins; D010641:Phenotype; D016133:Polymerase Chain Reaction; D000644:Quaternary Ammonium Compounds / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014169:Transformation, Bacterial / Q000235:genetics
D001426:Bacterial Proteins; D017931:DNA Primers; D008565:Membrane Proteins; D008744:Methylamines; C085245:NrgA protein, Bacillus subtilis; C085246:NrgB protein, Bacillus subtilis; D051922:PII Nitrogen Regulatory Proteins; D000644:Quaternary Ammonium Compounds; D014157:Transcription Factors; C027451:methylamine