title: Increased pyruvate orthophosphate dikinase activity results in an alternative gluconeogenic pathway in Rhizobium (Sinorhizobium) meliloti.
abstract: The formation of phosphoenolpyruvate (PEP) is a major step in the gluconeogenic pathway in which tricarboxylic acid (TCA) cycle intermediates are converted to hexose sugars. In Rhizobium (now Sinorhizobium) meliloti this step is catalysed by the enzyme PEP carboxykinase (PCK) which converts oxaloacetate to PEP. R. meliloti Pck- mutants grow very poorly with TCA cycle intermediates as the sole source of carbon. Here, the isolation and mapping of suppressor mutations which allow Pck- mutants to grow on succinate and other TCA cycle intermediates is reported. Tn5 insertions which abolished the suppressor phenotype and mapped to the suppressor locus were located within the pod gene encoding pyruvate orthophosphate dikinase (PPDK). Strains carrying suppressor mutations had increased PPDK activity compared to the wild-type. The suppressor phenotype was dependent on the combined activities of malic enzyme and PPDK, which thus represent an alternative route for the formation of PEP in R. meliloti. PPDK activity was not required for symbiotic N2 fixation.
authors.affiliation: Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, CanadaL8S 4K1.
authors.forename: Østerås
authors.initials: Ø
authors.lastname: Magne
authors.affiliation: Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, CanadaL8S 4K1.
authors.forename: Brian T
authors.initials: BT
authors.lastname: Driscoll
authors.affiliation: Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario, CanadaL8S 4K1.
authors.forename: Turlough M
authors.initials: TM
authors.lastname: Finan
mesh_terms: D000483:Alleles; D001426:Bacterial Proteins / Q000378:metabolism*; D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial / Q000235:genetics; D003227:Conjugation, Genetic; D004251:DNA Transposable Elements / Q000235:genetics; D005798:Genes, Bacterial; D016153:Genes, Suppressor; D005943:Gluconeogenesis; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009586:Nitrogen Fixation; D010728:Phosphoenolpyruvate / Q000378:metabolism; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism; D011772:Pyruvate, Orthophosphate Dikinase / Q000235:genetics / Q000378:metabolism*; D016962:Sinorhizobium meliloti / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development
chemical_list: D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D010728:Phosphoenolpyruvate; D011772:Pyruvate, Orthophosphate Dikinase; D010729:Phosphoenolpyruvate Carboxykinase (GTP)