Glutamine biosynthesis and the utilization of succinate and glutamine by Rhizobium etli and Sinorhizobium meliloti.
Sinorhizobium meliloti 1021 and Rhizobium etli CE3 turn over nitrogen and carbon from glutamine to ammonium and CO2, respectively. Some of the ammonium released is assimilated back into glutamine, indicating that a glutamine cycle similar to that in Neurospora operates in Rhizobium. In addition, a previously unrecognized metabolic pathway in Rhizobium was discovered--namely, conversion of glutamine-carbon to gamma-hydroxybutyric acid and beta-hydroxybutyric acid. Additionally, some of the 2-oxoglutarate derived from glutamine catabolism in Rhizobium is converted to succinate in glutamine-containing medium. Both S. meliloti 1021 and R. etli CE3 oxidize succinate preferentially over glutamine when provided with both carbon sources. In contrast to Sinorhizobium meliloti 1021 and Rhizobium etli CE3, an S. meliloti double mutant that lacks both glutamine synthetase (GS) I and II preferentially oxidizes glutamine over succinate when supplied with both substrates. GSII activity is induced in wild-type S. meliloti 1021 and R. etli CE3 grown in succinate-glutamine medium, and this enzyme participates in the cycling of glutamine-carbon and -nitrogen. On the other hand, GSII activity is repressed in both micro-organisms when glutamine is the only carbon source. These findings show that, in medium containing both glutamine and succinate, glutamine synthesis helps drive the utilization of succinate. When glutamine is in excess as an energy-providing substrate its synthesis is restricted, allowing for more effective utilization of glutamine as an energy source.
Departamento de Ecologie Molecular, Centro de Investigación Sobre Fijación de N itrogeno, Universidad National Autónoma de MexicoApartado Postal 56 5-A, Cuernavaca, MorelosMexico.
Sergio
S
Encarnación
Departamento de Biotecnologia, Instituto de lnvestigaciones Biomedicas, Universidad Nacional Autónoma de MexicoAparto Postal 70228Mexico.
Jorge
J
Calderón
Departments of Biochemistry3 and Cornell University Medical CollegeNew York, NYUSA.
Alan S
AS
Gelbard
Neurology and Neuroscience4, Cornell University Medical CollegeNew York, NYUSA.
Arthur J L
AJL
Cooper
Departamento de Ecologie Molecular, Centro de Investigación Sobre Fijación de N itrogeno, Universidad National Autónoma de MexicoApartado Postal 56 5-A, Cuernavaca, MorelosMexico.
Jaime
J
Mora
D000596:Amino Acids / Q000378:metabolism; D002244:Carbon / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000235:genetics / Q000378:metabolism; D005973:Glutamine / Q000096:biosynthesis* / Q000378:metabolism*; D007700:Kinetics; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D010084:Oxidation-Reduction; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012231:Rhizobium / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D016962:Sinorhizobium meliloti / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D019802:Succinic Acid / Q000378:metabolism*
D000596:Amino Acids; D000644:Quaternary Ammonium Compounds; D005973:Glutamine; D002244:Carbon; D019802:Succinic Acid; C083818:glutamine synthetase 2; C081173:glutamine synthetase I; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen