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  • Key wordsCorynebacterium glutamicum  (2)
  • Sinorhizobium meliloti  (2)
  • Springer  (4)
  • 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: 1432-072X
    Keywords: Key wordsCorynebacterium glutamicum ; Biotin ; carboxylase ; Biotin-carboxyl-carrier protein ; Acetyl-CoA carboxylase ; Fatty acid synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Following the analysis of transposon Tn5432-induced mutants of Corynebacterium glutamicum ATCC 13032, a gene encoding a protein with a biotin-binding motif was cloned. The DNA sequence of this gene revealed an open reading frame encoding 591 amino acids with a calculated mol. mass of 63.4 kDa. The protein is composed of two domains, an N-terminal biotin carboxylase and a C-terminal biotin-carboxyl-carrier protein, that are highly similar to corresponding subunits from prokaryotic and eukaryotic biotin enzymes. Over 70% identity was found to a protein from Mycobacterium leprae proposed to be part of an acyl-CoA carboxylase. Since it was not possible to inactivate the C. glutamicum gene, the gene most likely encodes a subunit of the essential acetyl-CoA carboxylase, which catalyzes the committed step in fatty acid synthesis.
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  • 3
    ISSN: 1432-072X
    Keywords: Key wordsCorynebacterium glutamicum ; Amino acid ; production ; Branched-chain amino acids ; Isoleucine ; uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract By complementation analysis of an isoleucine-uptake-deficient Escherichia coli strain, it was shown that a 1.6-kb HindIII-StuI fragment of Corynebacterium glutamicum ATCC 13032, located downstream of the aecD gene, encodes an isoleucine uptake system. Sequence analysis revealed that the complementing fragment carried an open reading frame, termed brnQ, that encodes a protein with sequence similarities to branched-chain amino acid carriers of gram-positive and gram-negative bacteria. The brnQ gene specifies a predominantly hydrophobic protein of 426 amino acid residues with a calculated molecular mass of 44.9 kDa. A topology prediction by neural network computer analysis suggests the existence of 12 hydrophobic segments that most probably form transmembrane α-helices. A C. glutamicum mutant strain harboring a defined deletion of brnQ in the chromosome showed a considerably lower isoleucine uptake rate of 0.04 nmol min–1 mg (dry mass)–1 as compared to the wild-type strain rate of 1.2 nmol min–1 mg (dry mass)–1. Overexpression of brnQ by means of a tac promotor resulted in an elevated uptake rate for isoleucine of 11.3 nmol min–1 mg (dry mass)–1. Evidently, the brnQ gene encodes the only transport system in C. glutamicum directing isoleucine uptake.
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  • 4
    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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