Evaluation of a Strategy for Identifying Nodulation Competitiveness Genes in Rhizobium Leguminosarum Biovar Phaseoli

Of 105 rhizobial isolates obtained from nodules of commonly cultivated legumes, we selected 19 strains on the basis of a high rate of symbiotic plant growth promotion. Individual strains within the species Rhizobium leguminosarum bv. trifolii , R. leguminosarum bv. viciae , and Rhizobium etli displayed variation not only in plasmid sizes and numbers but also in the chromosomal 16S–23S internal transcribed spacer. The strains were tagged with gusA gene and their competitiveness was examined in relation to an indigenous population of rhizobia under greenhouse conditions. A group of 9 strains was thus isolated that were competitive in relation to native rhizobia in pot experiments. Nineteen selected competitive and uncompetitive strains were examined with respect to their ability to utilize various carbon and energy sources by means of commercial Biolog GN2 microplate test. The ability of the selected strains to metabolize a wide range of nutrients differed markedly and the competitive strains were able to utilize more carbon and energy sources than uncompetitive ones. A major difference concerned the utilization of amino and organic acids, which were metabolized by most of the competitive and only a few uncompetitive strains, whereas sugars and their derivatives were commonly utilized by both groups of strains. A statistically significant correlation between the ability to metabolize a broad range of substrates and nodulation competitiveness was found, indicating that metabolic properties may be an essential trait in determining the competitiveness of rhizobia.

Download Full-text

THE NODULATION COMPETITIVENESS OF TN5-MUTANTS RHIZOBIUM LEGUMINOSARUM BV. VICIAE

Agriciltural microbiology ◽

10.35868/1997-3004.6.18-28 ◽

2008 ◽

Vol 6 ◽

pp. 18-28

Author(s):

O.D. Krugova ◽

N.M. Mandrovskaya

Keyword(s):

Aboveground Biomass ◽

Competitive Ability ◽

Rhizobium Leguminosarum ◽

High Nitrogen ◽

Nodule Number ◽

Industrial Strains ◽

Nodulation Competitiveness ◽

Tn5 Mutants ◽

Wild Strains ◽

Competition Ability

There has been studied the nodulation competitiveness of Tn5 mutants of pea rhizobia which were obtained from Rhizobium leguminosarum bv. viciae 263 б and which had high nitrogen fixing activity and promoted the increase of both nodule number and aboveground biomass in comparison with wild strains. It was shown that the competition ability of M1 and М68 mutants did not differ from the competitive ability of strains 263 б and Rhizobium leguminosarum bv. viciae 245 a of industrial strains.

Download Full-text

Plasmid-Encoded Catabolic Genes in Rhizobium leguminosarum bv. trifolii: Evidence for a Plant-Inducible Rhamnose Locus Involved in Competition for Nodulation

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi.1998.11.12.1175 ◽

1998 ◽

Vol 11 (12) ◽

pp. 1175-1185 ◽

Cited By ~ 53

Author(s):

Ivan J. Oresnik ◽

Laurie A. Pacarynuk ◽

Shelley A. P. O'Brien ◽

Christopher K. Yost ◽

Michael F. Hynes

Keyword(s):

Rhizobium Leguminosarum ◽

Wild Type Strain ◽

Genomic Library ◽

Carbon Sources ◽

Gene Replacement ◽

Catabolic Genes ◽

Nodulation Competitiveness ◽

Clover Root ◽

Derivatives Of ◽

Isogenic Strains

Cosmids carrying genes involved in utilization of rhamnose, sorbitol, and adonitol were isolated from a genomic library of Rhizobium leguminosarum by complementation of plasmid-cured derivatives of strain Rlt100 that were unable to grow on these carbon sources. Transposon mutagenesis was used to identify regions of each cosmid necessary for catabolism of the respective carbon source; partial DNA sequencing, as well as analysis of gene fusions created with transposon Tn5-B20, helped to determine the orientation and possible function of genes required for growth on the three substrates. Representative Tn5 insertions in the cosmids were recombined into the wild-type strain Rlt100 by gene replacement to generate isogenic strains unable to use either rhamnose, sorbitol, or adonitol. These strains were tested for their nodulation competitiveness compared with Rlt100 in co-inoculation experiments on clover plants. While sorbitol and adonitol catabolic mutants were unaltered in their competitive behavior, the nodulation competitiveness of three different rhamnose utilization mutants was significantly impaired. This result, coupled with the fact that the rhamnose catabolic genes were inducible by clover root extracts, suggests an important role for rhamnose catabolism in the early stages of the interaction of R. leguminosarum with clover plants. Hybridization studies with probes derived from the rhamnose, sorbitol, and adonitol catabolic loci demonstrated that these genes are plasmid encoded in virtually all R. leguminosarum strains, including representatives from all three biovars from a variety of different geographic locations.

Download Full-text

Early production of rhizopine in nodules induced bySinorhizobium melilotistrain L5-30

Canadian Journal of Microbiology ◽

10.1139/w00-136 ◽

2001 ◽

Vol 47 (2) ◽

pp. 165-171 ◽

Cited By ~ 16

Author(s):

K Heinrich ◽

M H Ryder ◽

P J Murphy

Keyword(s):

Sinorhizobium Meliloti ◽

Rhizobium Leguminosarum ◽

Fold Increase ◽

Gas Chromatography Mass Spectrometry ◽

Post Inoculation ◽

Infection Threads ◽

Nodulation Competitiveness ◽

Meliloti Strain ◽

Early Production ◽

Early Effects

The rhizopine L-3-O-methyl-scyllo-inosamine (3-O-MSI) is metabolized by approximately 10% of the strains of Rhizobium leguminosarum bv. viciae and Sinorhizobium meliloti. Rhizopine strains enjoy a substantial competitive advantage in nodulation, which is manifest before 14 days post-inoculation, implying that rhizopine is produced before this time. We were able to detect this compound in the roots of alfalfa (Medicago sativum L. cv. Hunter River) four days after germination (six days post-infection) with S. meliloti strain L5-30 by gas chromatography-mass spectrometry (GC-MS). At four days, nodules were not visible, and the concentration of rhizopine was extremely low, estimated at 67 pg/gfw (picograms/gram fresh weight). The amount increased gradually but remained low until 16 days, when there was a 50-fold increase from day four, by which time nodules were well established. This pattern of synthesis is consistent with previous studies indicating that rhizopine synthesis is regulated by nifA/ntrA regulatory genes, which are maximally expressed in bacteroids at the onset of nitrogen fixation. However, the low level of rhizopine synthesis must be responsible for the early effects on competition for nodulation. Production of rhizopine at this time most likely results from micro-aerobic induction of mos genes in free-living bacteria, either in the infection threads or in the rhizosphere.Key words: Medicago sativum, nodulation competitiveness, Rhizobium, rhizopine, Sinorhizobium meliloti.

Download Full-text