A phosphate transport system is required for symbiotic nitrogen fixation by Rhizobium meliloti

• Published in: Journal of Bacteriology Vol. 178; no. 15; pp. 4540 - 4547
• Main Authors: Bardin, S. (McMaster University, Hamilton, Ontario, Canada.), Dan, S, Osteras, M, Finan, T.M
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.08.1996
• Subjects: Amino Acid Sequence; ANION; ANIONES; ARN MENSAJERO; ARN MESSAGER; BACTERIA; Bacterial Proteins - genetics; Bacteriology; Base Sequence; Biochemistry; Biological Transport, Active - genetics; Chromosome Mapping; COMPOSICION QUIMICA; COMPOSITION CHIMIQUE; DNA Primers - genetics; DNA, Bacterial - genetics; EXPRESION GENICA; EXPRESSION DES GENES; FIJACION DEL NITROGENO; FIXATION DE L'AZOTE; FOSFATOS; GENE; GENES; Genes, Bacterial; Hordeum vulgare; ION; IONES; LOCI; LOCUS; Medicago sativa - microbiology; MEMBRANAS CELULARES; MEMBRANE CELLULAIRE; Molecular Sequence Data; MUTANT; MUTANTES; Nitrogen; Nitrogen Fixation - genetics; Nitrogen Fixation - physiology; Phenotype; PHOSPHATE; Phosphates - metabolism; PROTEINAS; PROTEINE; RHIZOBIUM MELILOTI; SECUENCIA NUCLEOTIDICA; Sequence Homology, Amino Acid; SEQUENCE NUCLEOTIDIQUE; Sinorhizobium meliloti - genetics; Sinorhizobium meliloti - metabolism; Symbiosis - genetics; Symbiosis - physiology; TRANSPORT DES SUBSTANCES NUTRITIVES; TRANSPORTE DE NUTRIENTES
• ISSN: 0021-9193; 1098-5530; 1067-8832
• DOI: 10.1128/jb.178.15.4540-4547.1996

The bacterium Rhizobium meliloti forms N2-fixing root nodules on alfalfa plants. The ndvF locus, located on the 1,700-kb pEXO megaplasmid of R. meliloti, is required for nodule invasion and N2 fixation. Here we report that ndvF contains four genes, phoCDET, which encode an ABC-type transport system for the uptake of Pi into the bacteria. The PhoC and PhoD proteins are homologous to the Escherichia coli phosphonate transport proteins PhnC and PhnD. The PhoT and PhoE proteins are homologous to each other and to the E. coli phosphonate transport protein PhnE. We show that the R. meliloti phoD and phoE genes are induced in response to phosphate starvation and that the phoC promoter contains two elements which are similar in sequence to the PHO boxes present in E. coli phosphate-regulated promoters. The R. meliloti ndvF mutants grow poorly at a phosphate concentration of 2 mM, and we hypothesize that their symbiotic phenotype results from their failure to grow during the nodule infection process. Presumably, the PhoCDET transport system is employed by the bacteria in the soil environment, where the concentration of available phosphate is normally 0.1 to 1 micromolar