Study of a fructose-negative mutant of Rhizobium meliloti

Guezzar, M El

doi:10.1016/0378-1097(88)90337-0

Cited by 3 publications

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“…Furthermore, the inability of R. meliloti and R. leguminosarum mutants lacking fructokinase or phosphoglucose isomerase activity to grow with fructose as sole carbon source indicates that this sugar is accumulated in its nonphosphorylated form. In fact, fructose catabolism occurs by phosphorylation into fructose-6-phosphate and conversion into glucose-6-phosphate, prior to its metabolization via the Entner-Doudoroff pathway known to be present in these microorganisms (8,15,17). A periplasmic fructose-binding protein (FBP) has been detected recently in Agrobacterium radiobacter, a member of the family Rhizobiaceae, and Western blotting with antiserum to FBP has shown the presence of an immunologically similar protein in S. meliloti and R. leguminosarum (60).…”

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Fructose Uptake in Sinorhizobium meliloti Is Mediated by a High-Affinity ATP-Binding Cassette Transport System

et al. 2001

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By transposon mutagenesis, we have isolated a mutant of Sinorhizobium meliloti which is totally unable to grow on fructose as sole carbon source as a consequence of its inability to transport this sugar. The cloning and sequencing analysis of the chromosomal DNA region flanking the TnphoA insertion revealed the presence of six open reading frames (ORFs) organized in two loci, frcRS and frcBCAK, transcribed divergently. The frcBCA genes encode the characteristic components of an ATP-binding cassette transporter (FrcB, a periplasmic substrate binding protein, FrcC, an integral membrane permease, and FrcA, an ATP-binding cytoplasmic protein), which is the unique high-affinity (K m of 6 M) fructose uptake system in S. meliloti. The FrcK protein shows homology with some kinases, while FrcR is probably a transcriptional regulator of the repressor-ORFkinase family. The expression of S. meliloti frcBCAK in Escherichia coli, which transports fructose only via the phosphotransferase system, resulted in the detection of a periplasmic fructose binding activity, demonstrating that FrcB is the binding protein of the Frc transporter. The analysis of substrate specificities revealed that the Frc system is also a high-affinity transporter for ribose and mannose, which are both fructose competitors for the binding to the periplasmic FrcB protein. However, the Frc mutant was still able to grow on these sugars as sole carbon source, demonstrating the presence of at least one other uptake system for mannose and ribose in S. meliloti. The expression of the frcBC genes as determined by measurements of alkaline phosphatase activity was shown to be induced by mannitol and fructose, but not by mannose, ribose, glucose, or succinate, suggesting that the Frc system is primarily targeted towards fructose. Neither Nod nor Fix phenotypes were impared in the TnphoA mutant, demonstrating that fructose uptake is not essential for nodulation and nitrogen fixation, although FrcB protein is expressed in bacteroids isolated from alfalfa nodulated by S. meliloti wild-type strains.Carbohydrates represent one of the major structural building blocks of all organisms. In bacterial cells, three energydependent sugar uptake mechanisms have been characterized. One that is widely used operates by proton symport (19); this system belongs to the major facilitator superfamily MFS (43) and is used in Escherichia coli for the uptake of galactose, xylose, and lactose. A second system, the phosphoenolpyruvate:sugar phosphotransferase system (PTS), is found in many bacteria (44) and is the main transporter for glucose, fructose, mannose, and sucrose in many gram-negative bacteria (41). A third transport mechanism found in all three kingdoms is the periplasmic binding protein-dependent ATP-binding cassette (ABC)-type carrier (4). In bacteria, the ABC superfamily transports a wide range of substrates, including a variety of monosaccharides like arabinose or ribose as well as disaccharides such as maltose and tri-or higher oligosaccharides (43).Sinorhizobium meliloti i...

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Fructose Uptake in Sinorhizobium meliloti Is Mediated by a High-Affinity ATP-Binding Cassette Transport System

et al. 2001

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“…The relative unimportance of these sugars in N 2 fixation is further suggested by the findings that R. leguminosarum bv. trifolii [11] and R. meliloti [12] mutants incapable of utilizing these sugars are still able to form effective symbioses.…”

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confidence: 99%

Carbon metabolism in Bradyrhizobium japonicum bacteroids

McDermott

1989

FEMS Microbiology Letters

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SUMMARYCarbon metabolism in Bradyrhizobium japonicum bacteroids is reviewed. Additionally, the bacteroid tricarboxylic acid (TCA) cycle and its regulation under oxygen-limited conditions is considered, with emphasis on possible sites of TCA cycle rate-limiting reactions. Furthermore, kve consider other adaptive pathways that may be employed by these organisms while in symbiosis. These pathways include: (1) a poly-fl-hydroxybutyrate shunt, (2) a malate-aspartate shuttle, (3) an a-ketoglutarate-glutamate shunt, (4) a modified dicarboxylic acid cycle, and (5) fermentation pathways leading to lactate, acetaldehyde and ethanol. The effects of oxygen limitation on host carbon metabolism are also considered briefly. INTRODUCTIONLegume root nodules represent a unique ecological niche for Bradyrhizobium and Rhizobium.

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Genetic characterization of a Rhizobium meliloti lactose utilization locus

Jelesko

Leigh

1994

Molecular Microbiology

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We identified several linked genes of a lactose regulon in Rhizobium meliloti. These were lacZ, the structural gene for beta-galactosidase; lacR, the lactose repressor gene; and two genes encoding proteins of unknown function, lacW and lacX. Insertion mutants in lacW and lacZ belonged to a single genetic complementation group, and lacW appeared to lie upstream of lacZ in an operon. Expression of lacZ, lacW and lacX was repressed by lacR, and expression of lacZ and lacW was derepressed by lactose. lacZ was not required for induction of lacW by lactose, suggesting that lactose itself, rather than a processed form of lactose, may be the actual inducer molecule. Expression of all three genes was repressed by succinate, and the lacR independence of this repression showed that inducer exclusion could not be the sole mechanism. This pattern of lac gene organization and regulation differs in several ways from that observed in enteric bacteria.

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Study of a fructose-negative mutant of Rhizobium meliloti

Cited by 3 publications

References 13 publications

Fructose Uptake in Sinorhizobium meliloti Is Mediated by a High-Affinity ATP-Binding Cassette Transport System

Fructose Uptake in Sinorhizobium meliloti Is Mediated by a High-Affinity ATP-Binding Cassette Transport System

Carbon metabolism in Bradyrhizobium japonicum bacteroids

Genetic characterization of a Rhizobium meliloti lactose utilization locus

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