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  • 1
    Electronic Resource
    Electronic Resource
    Biocontrol strain Pseudomonas fluorescens CHA0 and its genetically modified derivative with enhanced biocontrol capability exert comparable effects on the structure of a Sinorhizobium meliloti population in gnotobiotic systems (1997)
    Springer
    Biology and fertility of soils 25 (1997), S. 240-244 
    Details
    ISSN: 1432-0789
    Keywords: Key words Ecological impact ; Genetically modified ; organisms ; Microcosm studies ; Symbiotic nitrogen ; fixation ; Plant-beneficial bacteria ; Sinorhizobium meliloti
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The impact of biocontrol strain Pseudomonas fluorescens CHA0 and of its genetically modified, antibiotic-overproducing derivative CHA0/pME3424 on a reconstructed population of the plant-beneficial Sinorhizobium meliloti bacteria was assessed in gnotobiotic systems. In sterile soil, the final density of the reconstructed S. meliloti population decreased by more than one order of magnitude in the presence of either of the Pseudomonas strains when compared to a control without addition of P. fluorescens. Moreover, there was a change in the proportion of each individual S. meliloti strain within the population. Plant tests also revealed changes in the nodulating S. meliloti population in the presence of strains CHA0 or CHA0/pME3424. In both treatments one S. meliloti strain, f43, was significantly reduced in its root nodule occupancy. Analysis of alfalfa yields showed a slight but statistically significant increase in shoot dry weight when strain CHA0 was added to the reconstructed S. meliloti population whereas no such effect was observed with CHA0/pME3424.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003740050309
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  • 2
    Electronic Resource
    Electronic Resource
    The Sinorhizobium meliloti MucR protein, which is essential for the production of high-molecular-weight succinoglycan exopolysaccharide, binds to short DNA regions upstream of exoH and exoY (1998)
    Springer
    Molecular genetics and genomics 257 (1998), S. 433-441 
    Details
    ISSN: 1617-4623
    Keywords: Key words Regulation of gene expression ; Sinorhizobium meliloti ; Rhizobium meliloti ; Exopolysaccharide biosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sinorhizobium meliloti (Rhizobium meliloti) is able to produce two different exopolysaccharides, succinoglycan and galactoglucan. Mutations in the mucR gene of S. meliloti result in the stimulation of galactoglucan synthesis, while the type of succinoglycan produced is modified. In culture supernatants of a mucR mutant, low-molecular-weight succinoglycan is present, whereas no high-molecular-weight succinoglycan could be detected. The biosynthesis of succinoglycan is directed by the products of the exo gene cluster. Two DNA fragments from this cluster, one located in front of the exoH gene and one in the intergenic region between the divergently transcribed genes exoX and exoY, were shown to represent effective binding sites for MucR. Whereas the latter binding site contains an inverted repeat motif, the former does not. However, the binding of MucR did not strongly modify the transcription of the exo genes involved. In the mucR mutant the expression levels of exoH-lacZ and exoX-lacZ transcriptional fusions were found to be increased 1.5- and 1.7-fold, respectively. On the other hand, the expression level of an exoY-lacZ transcriptional fusion was found to be 1.5-fold lower in the mucR mutant than in the wild-type background. Comparison of the DNA sequences of MucR-binding sites provides insight into the structural requirements for binding of MucR.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004380050667
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  • 3
    Electronic Resource
    Electronic Resource
    Characterization of recA genes and recA mutants of Rhizobium meliloti and Rhizobium leguminosarum biovar viciae (1991)
    Springer
    Molecular genetics and genomics 229 (1991), S. 86-95 
    Details
    ISSN: 1617-4623
    Keywords: Rhizobium meliloti ; Rhizobium leguminosarum bv. viciae ; recA ; Homologous recombination ; Symbiotic nitrogen fixation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary DNA fragments carrying the recA genes of Rhizobium meliloti and Rhizobium leguminosarum biovar viciae were isolated by complementing a UV-sensitive recA − Escherichia coli strain. Sequence analysis revealed that the coding region of the R. meliloti recA gene consists of 1044 by coding for 348 amino acids whereas the coding region of the R. leguminosarum bv. viciae recA gene has 1053 bp specifying 351 amino acids. The R. meliloti and R. leguminosarum bv. viciae recA genes show 84.8% homology at the DNA sequence level and of 90.1% at the amino acid sequence level. recA − mutant strains of both Rhizobium species were constructed by inserting a gentamicin resistance cassette into the respective recA gene. The resulting recA mutants exhibited an increased sensitivity to UV irradiation, were impaired in their ability to perform homologous recombination and showed a slightly reduced growth rate when compared with the respective wild-type strains. The Rhizobium recA strains did not have altered symbiotic nitrogen fixation capacity. Therefore, they represent ideal candidates for release experiments with impaired strains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00264217
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  • 4
    Electronic Resource
    Electronic Resource
    The persistence of bioluminescent Rhizobium meliloti strains L1 (RecA-) and L33 (RecA+) in non-sterile microcosms depends on the soil type, on the co-cultivation of the host legume alfalfa and on the presence of an indigenous R. meliloti population (1997)
    Springer
    Plant and soil 188 (1997), S. 257-266 
    Details
    ISSN: 1573-5036
    Keywords: biological containment ; firefly luciferase ; microcosm studies ; recA ; Rhizobium meliloti ; rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In comparative analyses the influence of soil type, the rhizosphere of plants and the presence of an indigenous R. meliloti population on the population dynamics of bioluminescent R. meliloti strains L1 (RecA-) and L33 (RecA+) was assessed in microcosm studies. Both strains established better in a loamy and a clayey soil compared to a sandy soil. RecA- strain L1 showed a slightly but statistically significant reduced survival ability compared to RecA+ strain L33 (p ≤ 0.05). The presence of the host plant alfalfa stimulated the growth of both strains in non-sterile soil and no differences in the survival between both strains were observed. Co-cultivation of clover or wheat plants, respectively, neither positively nor negatively influenced the strains' survival. The most pronounced effect on the survival of both strains was exerted by the presence of an indigenous R. meliloti population. RecA- strain L1 showed a significantly impaired survival compared to RecA+ strain L33 (p ≤ 0.002). Moreover, no growth stimulation of strains L1 and L33 by the presence of the host plant alfalfa could be observed. These results indicate that the recA mutation affects the long-term rather than the short-term persistence of R. meliloti after environmental release.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004229819988
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