The C4-dicarboxylate transport system ofRhizobium meliloti and its role in nitrogen fixation during symbiosis with alfalfa (Medicago sativa)

1994 ◽  
Vol 50 (10) ◽  
pp. 874-883 ◽  
Author(s):  
D. Jording ◽  
C. Uhde ◽  
R. Schmidt ◽  
A. Pühler
Keyword(s):  
Nitrogen Fixation ◽  
Medicago Sativa ◽  
Transport System ◽  
Dicarboxylate Transport ◽  
Ofrhizobium Meliloti

Overexpression of the dctA gene in Rhizobium meliloti: effect on transport of C4 dicarboxylates and symbiotic nitrogen fixation

1992 ◽  
Vol 38 (6) ◽  
pp. 555-562 ◽  
Author(s):  
Vipin Rastogi ◽  
Monika Labes ◽  
Turlough Finan ◽  
Robert Watson
Keyword(s):  
Nitrogen Fixation ◽  
Acetylene Reduction ◽  
Symbiotic Nitrogen Fixation ◽  
Plasmid Stability ◽  
Rhizobium Meliloti ◽  
Mrna Synthesis ◽  
Dicarboxylate Transport ◽  
Fusion Strain ◽  
Tryptophan Operon ◽  
Specific Mrna

Symbiotic nitrogen fixation may be limited by the transport of C4 dicarboxylates into bacteroids in the nodule for use as a carbon and energy source. In an attempt to increase dicarboxylate transport, a plasmid was constructed in which the Rhizobium meliloti structural transport gene dctA was fused to a tryptophan operon promoter from Salmonella typhimurium, trpPO. This resulted in a functional dctA gene that was no longer under the control of the dctBD regulatory genes, but the recombinant plasmid was found to be unstable in R. meliloti. To stably integrate the trpPO-dctA fusion, it was recloned into pBR325 and recombined into the R. meliloti exo megaplasmid in the dctABD region. The resultant strain showed constitutive dctA-specific mRNA synthesis which was about 5-fold higher than that found in fully induced wild-type cells. Uptake assays showed that [14C]succinate transport by the trpPO-dctA fusion strain was constitutive, and the transport rate was the same as that of induced control cells. Acetylene reduction assays indicated a significantly higher rate of nitrogen fixation in plants inoculated with the trpPO-dctA fusion strain compared with the control. Despite this apparent increase, the plants had the same top dry weights as those inoculated with control cells. Key words: acetylene reduction, genetic engineering, nodule, plasmid stability, promoter.

scholarly journals EFFETS DES SOUCHES DE RHIZOBIUM MELILOTI ET DES COUPES SUCCESSIVES DE LA LUZERNE (MEDICAGO SATIVA) SUR LA FIXATION SYMBIOTIQUE D’AZOTE

1977 ◽  
Vol 57 (2) ◽  
pp. 433-439 ◽  
Author(s):  
L. M. BORDELEAU ◽  
H. ANTOUN ◽  
R. A. LACHANCE
Keyword(s):  
Nitrogen Fixation ◽  
Medicago Sativa ◽  
Statistical Study ◽  
Symbiotic Nitrogen Fixation ◽  
Rhizobium Meliloti ◽  
Dry Weight ◽  
Indirect Measurement ◽  
Controlled Environment ◽  
Symbiotic Efficiency ◽  
Plant Yield

Symbiotic nitrogen fixation with 49 isolates of Rhizobium meliloti was studied under controlled environment with alfalfa cv. Saranac. It was shown that plant yield in dry weight can be used as an indirect measurement of nitrogen fixation, and as a criterion for selecting efficient strains of R. meliloti. Statistical study on yields of three cuttings has established that the second cutting gives the most necessary information to correctly evaluate the symbiotic efficiency of the isolates. Six very efficient strains were selected.

scholarly journals New Substrates for the Dicarboxylate Transport System of Sinorhizobium meliloti

2000 ◽  
Vol 182 (15) ◽  
pp. 4216-4221 ◽  
Author(s):  
Svetlana Yurgel ◽  
Michael W. Mortimer ◽  
Kimberly N. Rogers ◽  
Michael L. Kahn
Keyword(s):  
Dicarboxylic Acid ◽  
Transport System ◽  
Sinorhizobium Meliloti ◽  
Monocarboxylic Acid ◽  
Dicarboxylic Acids ◽  
Carbonyl Groups ◽  
Nitrogen Fixing ◽  
Extended Conformation ◽  
Dicarboxylate Transport ◽  
Succinamic Acid

ABSTRACT The dicarboxylate transport (Dct) system of Sinorhizobium meliloti, which is essential for a functional nitrogen-fixing symbiosis, has been thought to transport only dicarboxylic acids. We show here that the permease component of the Dct system, DctA, can transport orotate, a monocarboxylic acid, with an apparentKm of 1.7 mM and a V maxof 163 nmol min−1 per mg of protein in induced cells. DctA was not induced by the presence of orotate. The transport of orotate was inhibited by several compounds, including succinamic acid and succinamide, which are not dicarboxylic acids. The dicarboxylic acid maleate (cis-butenedioic acid) was not an inhibitor of orotate transport, which suggests that it was not recognized by DctA. However, maleate was an excellent inducer of DctA expression. Our evaluation of 17 compounds as inducers and inhibitors of transport suggests that substrates recognized by S. meliloti DctA must have appropriately spaced carbonyl groups and an extended conformation, while good inducers are more likely to have a curved conformation.

scholarly journals THE ELECTION TRANSPORT SYSTEM IN NITROGEN FIXATION BY Azotobacter, I. AZOTOFLAVIN AS AN ELECTRON CARRIER

1969 ◽  
Vol 64 (3) ◽  
pp. 1079-1086 ◽  
Author(s):  
J. R. Benemann ◽  
D. C. Yoch ◽  
R. C. Valentine ◽  
D. I. Arnon
Keyword(s):  
Nitrogen Fixation ◽  
Transport System ◽  
Electron Carrier
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