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  • 1
    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.
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  • 2
    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.
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  • 3
    ISSN: 1573-5028
    Keywords: Rhizobium meliloti ; symbiotic nitrogen fixation ; nif genes ; expression in E. coli minicells ; Tn5 mutagenesis ; determination of coding regions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract An EcoRI fragment of Rhizobium meliloti M2011 which shows homology to Klebsiella pneumoniae DNA carrying nifH and nifD was cloned in both orientations into the Cm gene of plasmid pACYC184 and expressed in Escherichia coli minicells. Fragment specific polypeptides of Mr 12 500, 21 000, 30 000, and 31 000 could be identified. By transposon mutagenesis it was shown that two of them (Mr 12 500 and 21 000) are fusion products with parts of the chloramphenicol acetyltransferase. The other two polypeptides are specified by one coding region which could be mapped by transposon mutagenesis. There are several reasons (homology to Klebsiella nifH, sequence data and molecular weight of the gene products) to assume that this coding region represents the R. meliloti nifH gene (gene for the subunit of the R. meliloti nitrogenase reductase, RmII).
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Molecular genetics and genomics 211 (1988), S. 424-429 
    ISSN: 1617-4623
    Keywords: Streptomyces ghanaensis ; Tn5 mutagenesis ; Replication probe vectors ; Minimal replicon ; Shuttle vectors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cryptic plasmid pSG5 of Streptomyces ghanaensis 5/1B (DSM 2932) was characterized to have a molecular size of 12.7 kb and an approximate copy number of 20–50 per chromosome. A bifunctional derivative, designated pSW344E, consisting of pSG5 and an Escherichia coli vector plasmid was constructed. Following Tn5 mutagenesis in E. coli, the replication functions of the mutagenized pSW344E plasmids were analysed in S. lividans. A 2 kb DNA fragment of the pSG5 replicon was found to carry replication functions. Subcloning of pSG5 DNA into various replication probe vectors resulted in the identification of the pSG5 minimal replicon, identical to the above mentioned 2 kb DNA region. Several small bifunctional plasmids, able to replicate in E. coli as well as in Streptomyces, were generated during subcloning. Some of these plasmids were found to be useful shuttle vectors.
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