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  • 1
    Electronic Resource
    Electronic Resource
    Competitiveness and communication for effective inoculation byRhizobium, Bradyrhizobium and vesicular-arbuscular mycorrhiza fungi (1994)
    Springer
    Cellular and molecular life sciences 50 (1994), S. 884-889 
    Details
    ISSN: 1420-9071
    Keywords: Bradyrhizobium ; communication ; competitiveness ; Rhizobium ; vesicular-arbuscular (VA) mycorrhiza fungi
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract After a short summary on the ecology and rhizosphere biology of symbiotic bacteria and vesicular-arbuscular (VA) mycorrhiza fungi and their application as microbial inocula, results on competitiveness and communication are summarized. Stress factors such as high temperature, low soil pH, aluminium concentrations and phytoalexins produced by the host plants were studied withRhizobium leguminosarum bv.phaseoli andRhizobium tropici onPhaseolus beans. Quantitative data for competitiveness were obtained by usinggus + (glucoronidase) labelled strains, which produce blue-coloured nodules. ForPhaseolus-nodulating rhizobia, a group specific DNA probe was also developed, which did not hybridize with more than 20 other common soil and rhizosphere bacteria. Results from several laboratories contributing to knowledge of signal exchange and communication in theRhizobium/Bradyrhizobium legume system are summarized in a new scheme, including also defense reactions at the early stages of legume nodule initiation. Stimulating effects of flavonoids on germination and growth of VA mycorrhiza fungi were also found. A constitutive antifungal compound in pea roots, β-isoxazolinonyl-alanine, was characterized.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01923474
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  • 2
    Electronic Resource
    Electronic Resource
    Nodulation competitiveness of Rhizobium leguminosarum bv. phaseoli and Rhizobium tropici strains measured by glucuronidase (gus) gene fusion (1992)
    Springer
    Biology and fertility of soils 14 (1992), S. 140-144 
    Details
    ISSN: 1432-0789
    Keywords: Nodulation ; Competitiveness ; Rhizobium leguminosarum bv. phaseoli ; Rhizobium tropici ; Glucuronidase operon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The nodulation competitiveness of 17 Rhizobium leguminosarum bv. phaseoli and 3 R. tropici strains was analysed in growth pouches, at pH 5.2 and 6.4. All 20 strains were coinoculated with a gus + strain of R. leguminosarum bv. phaseoli strain KIM5s. The gus+ phenotype, carrying the glucuronidase gene, was used to type nodules directly in the growth pouches. Nodule occupancy ranged from 4% for the least competitive to 96% for the most competitive R. leguminosarum bv. phaseoli strain. The R. tropici strains showed low rates of nodule occupancy at pH 6.4 but their competitiveness improved significantly under acid conditions. CIAT 895 was the only R. leguminosarum bv. phaseoli strain that was less competitive (P〈0.05) at the lower pH. The competitiveness of all the other R. leguminosarum bv. phaseoli strains was unaffected by pH. Various physiological and genetic properties of the strains were analysed in search of correlations with nodulation competitiveness. Hybridisation patterns with three different DNA probes (nif KDH, common nod genes, and hup genes) and the metabolism of 53 different C sources were compared. No general correlations were found between hybridisation or growth pattern and competitiveness. The less competitive R. tropici strains had a unique DNA hybridisation pattern and were not able to use shikimate, ferulate, coumarate, or asparagine as C sources. Most of the less competitive R. leguminosarum bv. phaseoli strains could not metabolize either ferulate or coumarate. This might indicate a relationship between nodulation competitiveness and the ability to degrade aromatic compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336264
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  • 3
    Electronic Resource
    Electronic Resource
    Exopolysaccharide (EPS) synthesis in Bradyrhizobium japonicum : sequence, operon structure and mutational analysis of an exo gene cluster (1998)
    Springer
    Molecular genetics and genomics 259 (1998), S. 161-171 
    Details
    ISSN: 1617-4623
    Keywords: Key words Exopolysaccharide ; Symbiosis ; Nodule development ; Transcriptional reporter ; Gene fusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The nucleotide sequence of a 8330-bp DNA fragment from Bradyrhizobium japonicum 110spc4 was determined. Sequence analysis revealed that six ORFs were present and the deduced amino acid sequences were homologous to enzymes involved in exopolysaccharide (EPS) biosynthesis. The genes appear to be organized into at least four different operons. One gene was found to be homologous to exoB, which encodes a UDP-galactose 4′-epimerase. Other ORFs were homologous to UDP-hexose transferases and one ORF showed similarity to Sinorhizobium (Rhizobium) meliloti ExoP, which has been suggested to be involved in EPS chain-length determination. A set of deletion and insertion mutants was constructed and the resulting B. japonicum strains were tested for their symbiotic traits. Deletion mutant ΔP22, which lacks the C-terminal part of ExoP, the UDP-hexose transferase ExoT and the N-terminal part of ExoB, shows a delayed nodulation phenotype and induces symptoms of plant defense reactions; its EPS does not contain galactose and no high molecular weight fraction is synthesized. In contrast, insertion mutant EH3, which expresses an exoP gene product that is truncated in its putative periplasmic domain, produced an EPS containing both HMW and LMW fractions. However, the interaction of EH3 with soybeans was severely perturbed. As a rule, only the initial steps of nodule formation were observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004380050801
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