Dissertations / Theses on the topic 'Rhizobium'
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1
Eggleston, Gillian. "Rhizobium gelling polysaccharides." Thesis, Cranfield University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317909.
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Bardin, Sylvie D. "Phosphate uptake in Rhizobium meliloti." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape16/PQDD_0011/NQ30071.pdf.
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Finnie, Christine. "Protein secretion by Rhizobium leguminosarum." Thesis, University of East Anglia, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.361420.
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WISNIEWSKI, JEAN-PIERRE. "Symbiose : lectines de rhizobium lupini." Orléans, 1993. http://www.theses.fr/1993ORLE2041.
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Les bacteries du genre rhizobium peuvent interagir avec les plantes legumineuses pour etablir une symbiose fixatrice d'azote qui permet la nutrition azotee de la plante a partir de l'azote de l'air. Cette association symbiotique se traduit par le developpement d'un organe racinaire nouveau, le nodule, que les bacteries colonisent. L'une des etapes cles de la nodulation implique l'attachement des bacteries fixatrices d'azote sur les cellules vegetales avant leur penetration au sein des tissus racinaires. En nous interessant plus particulierement aux interactions glycannes/proteines, nous nous sommes proposes, au cours de ce travail, de montrer l'existence de lectines associees a la surface de rhizobium lupini. Une etude spectrofluorimetrique utilisant les neoglycoproteines fluoresceinylees, ainsi que des tests d'hemagglutination, nous ont permis de mettre en evidence des activites lectine s a ph 5,0. Par chromatographie d'affinite, nous avons purifie une lectine specifique de l'-l-fucose a partir de la souche ll13. Cette proteine a une masse moleculaire relative de 19 000 et presente un point isoelectrique de 6,7. Dans le cadre de l'etude des interactions entre r. Lupini et son partenaire hote, nous avons extrait et fractionne des exsudats de lupinus albus. Nous avons montre que des composes phenoliques presents dans ces exsudats pouvaient moduler les activites lectines associees aux souches de r. Lupini. Ces exsudats ont egalement un effet chimioattractant sur les bacteries
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Poole, Philip. "Amino acid metabolism in Rhizobium." Thesis, Poole, Philip (1986) Amino acid metabolism in Rhizobium. PhD thesis, Murdoch University, 1986. https://researchrepository.murdoch.edu.au/id/eprint/51728/.
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Addition of a broad range of L-amino acids and several D-amino acids to washed cells of Rhizobium leguminosarum strains WU235 and MNF3841 grown on glucose/NH4Cl elicited a low rate of O2 consumption. L-Glutamate, L-glutamine, L-aspartate, L-asparagine, L-alanine or L-histidine served as the sole source of nitrogen and carbon for growth of strain WU235 and each caused a several-fold increase in the amino acid dependent O2 consumption. In all these cultures excess ammonia was liberated, with the quantity depending on the number of nitrogen atoms per amino acid molecule. A very high dicarboxylic acid dependent O2 consumption in cells of WU235 grown on aspartate was found to be due to the presence of aspartase (EC 4.3.1.1).
R. leguminosarum WU235 only expressed aspartase when grown on L-aspartate or L-asparagine as the sole carbon source. Cells grown on glucose plus L-aspartate, or fumarate plus L-aspartate, did not express aspartase. Although these results suggested catabolite control of an inducible enzyme, induction of aspartase could not be demonstrated. Aspartase-producing cells continued to synthesize the enzyme after repeated subculture on glucose plus NH4Cl. Cells grown in glucose plus NH4Cl and plated onto aspartate produced different colony sizes; the larger (0.1% of the total) expressed aspartase, while the smaller did not. At dilutions sufficient to exclude the large aspartase-producing colonies, all initial colonies were the same size. They later developed papillae or became cluster colonies and produced aspartase. The data suggest that strain WU235 is unable to produce aspartase unless a mutation occurs which leads to constitutive enzyme synthesis.
Rhizobium leguminosarum MNF3841 grown on glucose/NH4Cl constitutively transported several L-amino acids. Transport rates were elevated 1.5-4 fold after growth in the absence of anmonia. Uptake of L-glutamate, L-glutamine, L-asparagine and L-leucine was inhibited to varying extents by a broad range of L-amino acids. The use of structural analogues of Lglutanvate and metabolic inhibitors suggested that L-glutamate transport was an active process requiring the L-isaner to have a free alpha hydrogen and a free amino group. Cells loaded with either L-(14C) leucine or L-(14C) glutamate exhibited exchange with a wide range of amino acids. The apparent Km for L-glutamate transport was 81 nM and both Laspartate and L-alanine were competitive inhibitors of Lglutamate uptake. Thus there appears to be an extremely high affinity carrier for L-glutamate that is not only very sensitive to inhibition by L-aspartate but also capable of being inhibited by a broad range of amino acids at an order of magnitude higher concentration.
Batch cultures of R. leguminosarum MNF3841, R. leguminosarum WU235, R. phaseoli WU15, R. trifolii TA1 and R. meliloti WU38 used amnonia faster than glutamate when presented with an equimolar mixture of the two. Only the cowpea strain NGR234 used both nitrogen sources at the same rate. R. leguminosarum MNF3841 grew faster on ammonia than on glutamate as the nitrogen source. In chemostat culture grown under phosphate limitation strain MNF3841 did not release excess ammonia when grown on either mannitol/L-glutamate or fumarate/L-glutamate, showing that L-glutamate catabolism was tightly regulated to meet the cells nitrogen requirement. Furthermore the rate of consumption of ammonia was similar to that for L-glutamate when either was supplied as the sole nitrogen source. However with L-histidine or L-alanine as the nitrogen source large quantities of excess ammonia were released. When chemostat cultures of R. leguminosarum MNF3841 were supplied with an equimolar mixture of ammonia and Lglutamate, 81-100% of the nitrogen consumed was ammonia. Similarly with mixtures of L-glutamate/L-histidine or Lglutamate/ L-alanine almost no L-glutamate was consumed, a result attributable to the release of excess ammonia from either L-histidine or L-alanine. The use of 14C labelled fructose or L-glutamate suggested that the intra and extracellular L-glutamate pools were isolated. This indicated that the ammonia preference must be exerted by a restriction in Lglutamate transport. L-Glutamate transport rates were low in L-glutamate/NH4Cl containing chemostats, which suggests ammonia restricts L-glutamate transport both by repression and perhaps by inhibition by seme metabolic intermediate.
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Dooley, John J. "Molecular techniques for rhizobium identification." Thesis, University of Bath, 1997. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338595.
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Miller, Lance Delano. "Characterization of the Chemotaxis System of the Endosymbiotic Bacterium Rhizobium leguminosarum." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19707.
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Chemotaxis is the process by which motile bacteria navigate chemical gradients in order to position themselves in optimum environments for growth and metabolism. Sensory input from both the external environment and the internal cellular environment are sensed by chemotaxis transducers and transduced to a two-component system whose output interacts with the flagellum thereby regulating motility.
Chemotaxis has been implicated in establishing the endosymbiotic relationship between the motile alpha-proteobacterium Rhizobium leguminosarum biovar viciae and its host Pisum sativa, the pea plant. An approach combing bioinformatical sequence analysis, molecular genetics, and behavioral analysis was used to characterize the chemotaxis system of R. leguminosarum and determine its contribution to this bacterium s lifestyle.
A genome search revealed the presence of two chemotaxis gene clusters, che1 and che2. Homologs of each che cluster are major chemotaxis operons controlling flagellar motility in other bacterial species. For this reason we sought to determine the contribution of each che cluster to chemotaxis in R. leguminosarum. We found that while both che clusters contribute to the regulation of motility, che1 is the major che cluster controlling chemotaxis. Using competitive nodulation assays we determined that che1, but not che2, is essential for competitive nodulation.
The major che cluster, che1, encodes a chemotaxis transducer, IcpA-Rl, with a globin coupled sensor domain. Chemotaxis transducers with a globin coupled sensor domain comprise a large class of proteins found in bacteria and archaea. These proteins have been shown to bind heme and sense oxygen and are therefore termed HemATs for heme-binding aerotaxis transducers. However, sequence analysis of IcpA-Rl reveals that it lacks the requisite amino acid residues for heme-binding and is therefore unlikely to sense oxygen. We present evidence that IcpA-Rl is likely an energy transducer and represents a novel function of the globin coupled sensor domain in sensing energy related parameters.
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Thorne, Stephen Howard. "Stationary phase survival of Rhizobium leguminosarum." Thesis, Imperial College London, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265401.
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Seaman, Jonathan. "Signature-tagged mutagenesis in Rhizobium leguminosarum." Thesis, University of Reading, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499374.
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Rhizobia are a diverse group of symbiotic alpha-proteobacterial diazotrophs which enter a relationship with specific leguminous plants, in which the plant supplies the bacteria with required compounds whilst the bacteria reduce atmospheric nitrogen into ammonia that the plant uses as a nitrogen source. Modification of rhizobial strains has produced mutants more effective at fixing nitrogen, which in turn results in an increase in biomass of host plants under laboratory conditions but these strains are frequently out competed by wild-type strains in field studies or lost in the intervening years of a crop rotation. This study aimed to establish a library of mutants and a system for screening these strains en masse to identify some of the genes involved in competitive rhizosphere colonization in Rhizobium leguminosam.
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Fox, Marc A. "Adaptation of Rhizobium to environmental stress." Thesis, University of Reading, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427836.
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Abdel, Magid H. M., P. W. Singleton, and J. W. Tavares. "Sesbania-Rhizobium Specificity and Nitrogen Fixation." University of Arizona (Tucson, AZ), 1988. http://hdl.handle.net/10150/609114.
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The compatibility of potentially nitrogen fixing associations between ten Rhizobium strains and six Sesbania accessions (species) was studied under glasshouse conditions. The rates of N₂ (C₂ H₂) fixation (u moles C₂ H₄ /plant/h) were determined. The various Sesbania accessions responded differently to inoculation with the strains tested. The ANOVA test revealed that there are real accessions (P = 0.01) and strains (P = 0.05) differences. In general the results obtained indicated that the highest mean rate of N₂ (C₂ H₂) fixation and the highest degree of compatibility with strains under test was shown by Sesbania bispinosa (accession BA12). Sesbania grandiflora (accession GL 2.02) ranked next. The performance of Sesbania pachycarpa (accession PCI), Sesbania macrantha (accession MNI), and Sesbania sesban (accession SBIO) in the N₂ (C₂ H₂) assay is lower than that of accessions BAI2 and GL2.02, thus indicating the possibility of lack of compatibility between these three accessions and almost all of the Rhizobium strains studied. Plants of Sesbania rostrata (accession RSI) produced either extremely low or no ethylene (C₂ H₄) quantities in the N₂ (C₂ H₂) assay thus indicative of high specificity or that this legume is not promiscuous at all. However, inoculated and fertilized Sesbania rostrata performed quite satisfactorily and formed profuse N₂-fixing nodules on roots and stems when grown in potted soil under Central Saudi Arabia climatic conditions. The results obtained indicated high variability among treatments in nodule number.
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Chen, Yung-Pin. "Pathways of aromatic metabolism in Rhizobium." Thesis, Chen, Yung-Pin (1986) Pathways of aromatic metabolism in Rhizobium. PhD thesis, Murdoch University, 1986. https://researchrepository.murdoch.edu.au/id/eprint/51776/.
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Studies on the oxidation of a variety of aromatic substrates by Rhizobium trifolii TA1 and Rhizobium leguminosarum MNF3841 indicated that the former could oxidise aromatic substrates normally leading to the catechol or protocatechuate branches of the 3-oxoadipate pathway, while the latter could not use substrates like benzoate requiring the catechol branch. Assays for typical enzymes of the catechol and protocatechuate branches confirmed this conclusion. The detection of a catechol 2,3-dioxygenase only in R. trifolii TA1 further suggested the existence of a meta-cleavage pathway, though no further characterization of such a pathway was attempted.
The uptake systems for benzoate and 4-hydroxybenzoate were studied specifically in R. trifolii TA1 and for 4-hydroxybenzoate in R. leguminosarum. Both systems are active in nature, and both have a pattern of inhibition by aromatic substrates. The two transport systems were not cross-inducible in R. trifolii, but were induced by growth on the appropriate substrate. The transport systems for 4-hydroxybenzoate and protocatechuate also appeared to be distinct. A mutant defective in 4-hydroxybenzoate transport was also isolated.
Removal of periplasmic proteins by lysozyme-EDTA treatment of R. trifolii TA1 abolished 4-hydroxy-benzoate uptake activity in cells grown on 4-hydroxy-benzoate. Cells grown on succinate and treated similarly continued to transport succinate. The periplasmic protein fraction from 4-hydroxybenzoate-grown cells bound radioactive 4-hydroxybenzoate, but similar fractions from cells grown on glucose, succinate, protocatechuate or benzoate did not. A protein was purified from the hydroxybenzoate-grown cells which bound up to 1 mole of [l4C}-4-hydroxy-benzoate per mole of protein. It has been suggested that a binding protein may be required for the transport of 4-hydroxybenzoate.
The two dioxygenases involved in cleavage of the aromatic ring - protocatechuate 3,4-dioxygenase and catechol 1,2-dioxygenase were purified from R. trifolii TA1, and some of their biochemical properties established. In general, they show considerable resemblance to comparable enzymes purified from Pseudomonas species. Both appeared to be dependent on Fe(III) for activity; the iron could be removed from them by 1,10-phenanthroline after reduction, and activity restored only with an EDTA chelate of Fe(III). Both were extremely sensitive to inhibition by the EDTA chelates of Ni(III) and Al(III) where EDTA itself was ineffective. It has been suggested that inhibition of the dioxygenases by soil aluminium in highly acid soils might well prevent utilization of aromatic compounds by rhizobia and lead to poor survival.
The regulation of the pathways from 4-hydroxy-mandelate and L-mandelate to 4-hydroxybenzoate and catechol, respectively, was studied. Unlike the situation in many Pseudomonas species, the pathways from mandelate and 4-hydroxymandelate appear to involve quite distinct enzymes in R. trifolii TA1.
Studies of enzyme induction in the 4-hydroxy-mandelate and mandelate pathways to protocatechuate and catechol, respectively, suggested that induction of enzymes was sequential for all enzymes, though only a limited range of substrates was available for growth.
When cells were grown on particular substrates, and another substrate downstream from it added, the enzymes upstream showed lowered activities. This finding was true for both the mandelate and hydroxymandelate pathways and for those segments of the 3-oxoadipate pathway which were tested.
Cells grown on aromatic substrates in the presence of other carbon sources showed lowered activities of the enzymes of aromatic degradation. These activities occurred whether the non-aromatic substrate lower were a product of aromatic degradation (succinate or acetate) or glucose. It was not clear whether this represented an end-product type of repression or a limited catabolite repression.
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Guezzar, Mounir El. "Contribution à l'étude de la symbiose rhizobium-légumineuse : obtentions et études de deux mutants métaboliques de rhizobium meliloti." Lille 1, 1987. http://www.theses.fr/1987LIL10220.
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El, Guezzar Mounir. "Contribution à l'étude de la symbiose rhizobium-légumineuse obtentions et études de deux mutants métaboliques de Rhizobium meliloti /." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376056398.
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Ibrahim, Mohamed M. "Pyrimidine Metabolism in Rhizobium: Physiological Aspects of Pyrimidine Salvage." Thesis, University of North Texas, 1989. https://digital.library.unt.edu/ark:/67531/metadc330907/.
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The objective of this research was to study the pyrimidine salvage pathways of Rhizobium. Three approaches were used to define the pyrimidine salvage pathways operative in two species of Rhizobium, R. meliloti and R. leguminosarum . The first approach was to ascertain the pyrimidine bases and nucleosides that could satisfy the pyrimidine requirement of pyrimidine auxotrophs. Uracil, cytosine, uridine or cytidine all satisfied the absolute pyrimidine requirement. The second approach was to select for mutants resistant to 5-fluoropyrimidine analogues which block known steps in the interconversion of the pyrimidine bases and nucleosides. Mutants resistant to 5-fluorouracil lacked the enzyme uracil phosphoribosyltransferase (upp ) and could no longer use uracil to satisfy their pyrimidine requirement. Mutants resistant to 5-fluorocytosine, while remaining sensitive to 5- fluorouracil, lacked cytosine deaminase (cod) and thus could no longer use cytosine to satisfy their pyrimidine auxotrophy. The third approach used a reversed phase HPLC column to identify the products that accumulated when cytidine, uridine or cytosine was incubated with cell extracts of wild type and analogue resistant mutants of Rhizobium. When cytidine was incubated with cell extracts of Rhizobium wild type, uridine, uracil and cytosine were produced. This Indicated that Rhizobium had an active cytidine deaminase (cdd) and either uridine phosphorylase or uridine hydrolase. By dialyzing the extract and reincubating it with cytidine, uridine and uracil still appeared. This proved that it was a hydrolase ( nuh ) rather than a phosphorylase that degraded the nucleoside. Thus, Rhizobium was found to contain an active cytidine deaminase and cytosine deaminase with no uridine phosphorylase present. The nucleoside hydrolase was active with cytidine, uridine and to a far lesser extent with purines, adenosine and inosine. When high concentrations of cytidine were added to mutants devoid of hydrolase, cytosine was produced from cytidine - 5-monophosphate by the sequential action of uridine ( cytidine ) kinase and nucleoside monophosphate glycosylase. Both ft meliloti and ft leguminosarum had identical salvage pathways.
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Heinrich, Keith. "Ecological and molecular studies on rhizobial rhizopines." Title page, contents and summary only, 1999. http://web4.library.adelaide.edu.au/theses/09PH/09phh469.pdf.
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Corrigendum attached to back cover. Includes bibliographical references (leaves 160-190). Investigates the role of rhizopines in rhizobial competition for nodulation, and to isolate the rhizopine synthesis genes in Rhizobium leguminosarum bv. viciae.
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Lethbridge, Benjamin James. "The structure of trifolitoxin : A bacteriocin from Rhizobium leguminosarum biovar trifolii strain T24 /." Title page, table of contents and summary only, 1989. http://web4.library.adelaide.edu.au/theses/09PH/09phl647.pdf.
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Wexler, Margaret. "Molecular biology and distribution of rhizopine genes in Rhizobium species." Title page, contents and summary only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phw545.pdf.
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Kyei-Boahen, Stephen. "Evaluation of granular Rhizobium inoculant for chickpea." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0033/NQ63957.pdf.
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Latchford, J. W. "Genetic analysis of exopolysaccaride synthesis in Rhizobium." Thesis, University of East Anglia, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334211.
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Borthakur, D. "Molecular genetics of exopolysaccharide synthesis in Rhizobium." Thesis, University of East Anglia, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373728.
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Simpkins, Sean A. "The DnaK molecular chaperone of Rhizobium leguminosarum." Thesis, University of East Anglia, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.302035.
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Jones, M. A. "Molecular genetics of exopolysaccharide production in Rhizobium." Thesis, University of East Anglia, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384809.
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Johnson, Andrew C. "The mechanism of aluminium toxicity to rhizobium." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324290.
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Lusby, John. "Hemin Utilization in Rhizobium leguminosarum ATCC 14479." Digital Commons @ East Tennessee State University, 2021. https://dc.etsu.edu/etd/3897.
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Rhizobium leguminosarum is a Gram negative, motile, nitrogen-fixing soil bacterium. Due to the scarcity of iron in the soil bacteria have developed a wide range of iron scavenging systems. The two types of iron scavenging systems used are indirect and direct. In-silico analysis of the genome identified a unique direct iron scavenging system the Hmu operon. This system has been identified in other closely related rhizobium species and is believed to be involved in utilizing heme compounds as a sole source of iron. We have attempted to characterize the role of the Hmu operon in iron utilization by monitoring the growth of R. leguminosarum ATCC 14479 in hemin supplemented media. Growth curves show that it is capable of using hemin as a sole source of iron. The outer membrane profiles were analyzed for the presence of hemin binding proteins.
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Dalla, Venezia Nicole. "Etude des lipopolysaccharides d'entérobactéries et de rhizobium." Lyon 1, 1985. http://www.theses.fr/1985LYO12585.
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McKay, Ian. "Carbon metabolism in Rhizobium leguminosarum MNF 3841." Thesis, McKay, Ian (1988) Carbon metabolism in Rhizobium leguminosarum MNF 3841. PhD thesis, Murdoch University, 1988. https://researchrepository.murdoch.edu.au/id/eprint/51790/.
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So much depends upon a red wheel barrow glazed with rain water beside the white chickens - William Carlos Williams 1923.
Carbon catabolism of Rhizobium lequminosarum MNF3841 was studied in free-living cells grown in chemostat and in bacteroids.
Enzymes of the Entner-Doudoroff (ED) pathway, the pentose phosphate (PP) pathway and the TCA cycle were present, though the absence of phosphofruetokinase prec1uded the operation of the complete Embden- Meyerhof-Parnas (EMP) pathway. The low activity of fructose-bisphosphate aldolase in sugar-grown cells indicated that recycling of glyceraldehyde 3-phosphate (produced by the ED pathway) to fructose 6-phosphate is unlikely. Further catabolism of glyceraldehyde 3-phosphate is probably achieved via the enzymes of the latter part of the EMP pathway which were shown to be present in this organism.
In phosphate-limited chemostat culture the activities of invertase, glucose-6-phosphate de hydro- genase, the ED enzymes and 6-phosphogluconate dehydrogenase were two- to three-fold lower in cells grown on fumarate compared to the activities in cells grown on sucrose. Glucose-6-phosphate dehydrogenase also showed modulation of activity due to the nature of the growth limitation with oxygen-limited cells possessing only 50% of the activity of phosphate-limited cells when fumarate was the carbon source. None of the other sugar catabolic enzymes, nor any of those of the TCA cycle showed any modulation in response to the growth substrate or the nature of the growth limitation.
Since modulation of some sugar catabolic enzymes was demonstrated in free-living cells in response to growth substrate, the preferences of free-living cells for C4-dicarboxylates, or sugars, were further investigated. In chemostat culture under phosphate-limitation MNF3841 co-utilised fumarate in combination with glucose, or sucrose, or glucose plus fructose. A slight preference for Ca-dicarboxylates was indicated, since the inhibition of sugar utilisation by fumarate was greater than the inhibition of fumarate utilisation by equivalent concentrations of glucose, or sucrose, or glucose plus fructose.
Though the obvious importance of Ca-dicarboxylates as carbon sources for both free-living rhizobia and bacteroids is recognised, the ancillary enzymes required for their catabolism have not yet been identified. R. lequminosarum MNF3841 catabolised Ca-dicarboxylates and L-arabinose vi a the TCA cycle with the requirement for acetyl CoA being met by the action of malic enzyme and pyruvate dehydrogenase. Malic enzyme was present in sugar-grown free-living cells though higher levels were observed when fumarate or L-arabinose was the growth substrate. Manganese-dependent malic enzyme activity was evident with either NADP* or NAD* as the cofactor and the activity was stimulated by the presence of KC1. The activity of pyruvate dehydrogenase, which is also required for the catabolism of sugars via the TCA cycle, was higher in sucrose-grown cells than those grown on fumarate.
In addition to the TCA cycle and the ancillary enzymes (malic enzyme and pyruvate dehydrogenase) the growth of rhizobia on C4-dicarboxylates (and other substrates which feed into the TCA cycle such as L-glutamate, L-aspartate, L-histidine and L-arabinose) also requires a system of gluconeogenesis. This is accomplished in MHF3841 vi a phosphoenolpyruvate carboxykinase (PEPCK), fruetose-bisphosphate aldolase and fructose-bisphosphatase in conjunction with enzymes of the EMP pathway. In addition R. lequminosarum MNF3085, a PEPCK-deficient mutant, failed to grow on succinate, pyruvate, L-arabinose or L-glutamate, yet grew as well as MNF3841 on glucose, sucrose and glycerol showing that PEPCK is essential for gluconeogenesis.
PEPCK and fruetose-bisphosphate aldolase were rapidly derepressed following transfer of cells from a medium with sucrose as the carbon source to one with fumarate as the carbon source. In chemostat culture, the addition of 0.1 mM sucrose caused an 80% inhibition of PEPCK and fructose-bisphosphate aldolase synthesis and 0.4 mM sucrose caused complete inhibition of PEPCK synthesis.
Although Ca-dicarboxylate transport was rapidly inducible in free-living cells, bacteroids of MNF3841 isolated from pea nodules could immediately transport 1 4 C-succinate. Furthermore, blocking pyruvate dehydrogenase with arsenite resulted in bacteroids immediately accumulating pyruvate and malate from fumarate indicating that bacteroids in the nodules are in receipt of C*- dicarboxylates.
Bacteroids isolated on a Percoll gradient had activities of TCA cycle enzymes, pyruvate dehydrogenase and malic enzyme up to six-fold higher than those in free-living cells, whereas the activities of sugar catabolic enzymes in bacteroids were 2- to 14- fold lower than those in free-living cells grown on sucrose. These activities are a further indication that Ca-dicarboxylates (and not sugars) are the principal form of carbon catabolised by bacteroids.
Additionally bacteroids of MNF3841 contained low levels of PEPCK and fruetose-bisphosphate aldolase. The bacteroid-associated PEPCK activity was clearly of bacterial and not plant origin because of its nucleotide requirement and the fact that bacteroids of MNF3085 (PEPCK deficient in the free-living form) contained no PEPCK activity. MNF3085 nodulated and fixed nitrogen as effectively as t he parent which demonstrates that the capacity to synthesise sugars via gluconeogenesis is not required for an effective symbiosis. Thus these data suggest that although bacteroids of MNF 3085 receive sufficient sugar to compensate for their gluconeogenic defect, there is insufficient sugar available to bacteroids of the wild type to completely repress the synthesis of PEPCK. A low amount of sugar available to the bacteroid suggested by these data would be in keeping with the very low activities of sugar catabolic enzymes in the bacteroid. These data in conjunction with the transport of C4-dicarboxylates by bacteroids immediately after their isolation and the elevated activities of the enzymes of C4-dicarboxylate catabolism in bacteroids indicate that C4-dicarboxylates are indeed the major carbon substrate used by them for N2 fixation.
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Catlow, Helga Y. "Chemotaxis and motility of Rhizobium trifolii TA1." Thesis, Catlow, Helga Y. (1988) Chemotaxis and motility of Rhizobium trifolii TA1. PhD thesis, Murdoch University, 1988. https://researchrepository.murdoch.edu.au/id/eprint/51979/.
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The work in this thesis set out to examine the importance of motility and chemotaxis to the behaviour of Rhizobium trifolii TA1 in soil. Mutants defective in chemotaxis or motility were therefore generated by Tn5- mutagenesis (Beringer et a1., 1978) of Rhizobium trifolii TA1.
Attempts to produce totally non-chemotactic mutants of R. trifolii were unsuccessful, though several partially non-chemotactic mutants were isolated. These mutants lacked chemotaxis to a wide range of single carbon sources, but were responsive to yeast extract in every case. They were therefore considered unsuitable for investigating the role of chemotaxis in nodulation and migration of root nodule bacteria in soil, since the possibility remained that plant exudates or soil substrates could still elicit chemotactic responses.
Non-motile mutants were obtained using transposon Tn-5 mutagenesis. These mutants were indistinguishable from the wild type in growth rates in both laboratory media and in the clover rhizosphere. They also produced as many nodules on clover plants (Trifolium subterraneum cv Mount Barker) as the wild type and were as effective as the parent at nitrogen fixation.
When motile and non-motile (flagellate or nonflagellate) strains were inoculated simultaneously onto clover plants the non-motile strain was found in only about 15% of the resultant nodules and the motile strain in 85%. This implies that the non-motile mutants are at some disadvantage in competition with the motile parent.
The vertical movement of root nodule bacteria was examined in vertical columns of steam-treated sand. The non-motile strain did not move away from the inoculation site whereas the motile one did. Other experiments to determine the nodulation pattern of motile and non-motile organisms, on the tap roots of clover in steamed soil, showed that the motile strain could produce nodules further down the clover tap root than the non-motile strains. Similar experiments examining the lateral movement of both motile and non-motile strains from a central inoculated clover plant again showed that the motile strain had a definite advantage over the non-motile strain in its ability to move through steamed soil to produce nodules on clover roots.
When these experiments were carried out in untreated sand, quite different results were obtained. In experiments using soil columns to examine the vertical movement of root nodule bacteria, neither the motile or non-motile strains moved significantly from the inoculation point. Similarly, in experiments to examine lateral movement of root nodule bacteria, in non-treated soil, little movement of either motile or non-motile strain was observed.
These experiments showed that in steam-treated soil, motile strains, but not non-motile strains, have the capacity to move considerable distances. However, this movement potential may not be achieved under natural conditions in soil.
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Gomes, Douglas Fabiano. "Análise proteômica de Rhizobium tropici PRF 81." Universidade Estadual de Londrina. Centro de Ciências Exatas. Programa de Pós-Graduação em Biotecnologia, 2011. http://www.bibliotecadigital.uel.br/document/?code=vtls000166050.
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A estirpe PRF 81 (= SEMIA 4080) de Rhizobium tropici é utilizada no Brasil em inoculantes agrícolas para a cultura do feijoeiro (Phaseolus vulgaris L.) desde 1998, devido à sua alta eficiência em fixar nitrogênio, elevada competitividade com estirpes nativas e capacidade de adaptar-se a diferentes condições de estresse. Neste contexto, o objetivo deste estudo consistiu em obter uma visão geral das respostas adaptativas ao estresse térmico apresentadas pela estirpe PRF 81. A partir da separação por eletroforese bidimensional foram identificados, por espectrometria de massas MALDI-TOF/TOF-TOF, 59 proteínas diferencialmente expressas na condição de estresse, representada pela expressão diferencial no crescimento in vitro a 35 oC em comparação com a temperatura de 28 oC. As proteínas diferencialmente expressas, in vitro, a 35 oC pela PRF 81 foram associadas às classes funcionais do COG (Clusters of Orthologous Groups) de metabolismo, processos celulares e sinalização e processamento e armazenamento de informações. Dentre as proteínas induzidas pela temperatura elevada, duas são, frequentemente, associadas ao estresse térmico, sendo elas as chaperonas DnaK e GroEL. Diversas proteínas responsivas ao estresse oxidativo também tiveram expressão diferencial na temperatura de 35 oC, revelando assim a diversidade de adaptações a condições de estresse apresentados por esta estirpe, sugerindo ainda um -cross-talk" entre os estresses térmico e oxidativo. Assim, através da análise proteômica diferencial, foi possível caracterizar as respostas ao calor apresentadas pela estirpe PRF 81.Rhizobium tropici strain PRF 81 (= SEMIA 4080) is commercially used in inoculants to the common bean crop in Brazil since 1998 due its high efficiency in fixing nitrogen, competitiveness against indigenous rhizobial populations and capacity of adaptation to stressful of tropical environments. The objective of this study was to obtain an overview of adaptative responses to heat stress of PRF 81, by analyzing the differentially expressed proteins when the bacterium was grown at 28°C and 35°C. Two-dimensional gel electrophoresis (2-DE) revealed the differential expression of 59 proteins that were identified by MALDI-TOF/TOF-TOF. The in vitro up-regulated proteins were associated with functional classes of methabolism, cellular process and signaling and Information storage and processing of COG (Clusters of Orthologous Groups). Among the differentially expressed proteins, two are often related with heat stress; the DnaK and GroEL chaperones. Interestingly, several oxidative stress responsive proteins were up-regulated in 35°C, and these results reveal the diversity of adaptations presented by this thermo-tolerant strain to stress condictions, and suggests a cross talk between heat and oxidative stress. Therefore, the proteomics analysis allowed to characterize the responses to heat stress showed by PRF 81 strain.
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Rodpothong, Patsarin, and n/a. "Host-specific Nod factor requirements for nodulation of Lotus species by Mesorhizobium loti." University of Otago. Department of Microbiology & Immunology, 2008. http://adt.otago.ac.nz./public/adt-NZDU20080910.113419.
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Mesorhizobium loti possesses a symbiosis island (ICEMlSym[R7A]) that confers upon the bacterium the ability to form a symbiotic association with legumes of the genus Lotus. Nodulation (nod, nol and noe) genes located on the ICEMlSym[R7A] encode enzymes that are responsible for the production of a species-specific signaling molecule, named Nod factor. Perception of Nod factors by plant receptors triggers several plant responses and facilitates bacterial invasion, leading to the formation of root nodules. The studies in this thesis aimed to examine the impact of various structural components of the M. loti Nod factor on host specificity and recognition within Lotus species. The minimal gene requirement for eliciting nodule development on Lotus plants was also determined.
The M. loti strain R7A Nod factor has a backbone of five N-acetyl-D-glucosamine (GlcNAc) residues. The non-reducing terminal GlcNAc residue carries an acyl chain of either a vaccenic acid (C[18:1]) or palmitic acid (C[16:0]), a carbamoyl group and a methyl group, while an acetylfucose is present at the reducing terminus. Analysis of loss-of-function [Delta]nodZ and [Delta]nolL mutants showed that the acetylfucose at the reducing terminus was required for efficient nodulation of Lotus species, especially during the initiation of infection threads and for induction of symbiotic gene, NIN. Upon inoculation with R7A[Delta]nodZ, nodulation of Lotus corniculatus and L. filicaulis was significantly delayed and reduced, while only a delay in the onset of nodulation was observed with L. japonicus. Interestingly, nodulation of L. burttii induced by R7A[Delta]nodZ was as efficient as that induced by R7A. Hence, the absolute requirement for the acetylfucose during nodulation was host-dependent.
In planta complementation and domain swap experiments using transgenic L. japonicus nfr1 and nfr5 mutants were employed to investigate the role of the reducing terminal acetylfucose in the perception of Nod factor. Nodulation of complemented L. japonicus nfr1 and nfr5 mutants inoculated with R7A[Delta]nodZ was poor, whereas similar plants inoculated with R7A nodulated well. This suggests that the in planta complementation was inefficient and as a result accentuated the effect of the acetylfucose on the Nod factor recognition. The responses of recombinant inbred lines (RILs) derived from a cross between L. filicaulis and L. japonicus to inoculation with strain R7A[Delta]nodZ suggested that at least two genetic loci on chromosome 4, in addition to the Nfr1 and Nfr5 genes, contribute to Nod factor perception and in particular the host-specific recognition of the acetylfucose, This suggests the involvement of multiple receptors or a receptor with multiple components in the perception of Nod factors.
A gain-of-function study demonstrated that the presence of nodulation genes alone in nonsymbiotic mesorhizobia was sufficient to induce nodulation and bacteroid formation on Lotus plants, indicating that no other ICEMlSym[R7A] genes were required for infection thread formation or bacterial release. Nodulation assays of four Lotus species indicated host-specific requirements for nodulation genes. The presence of the nodA, nodC, nodD1, nodD2, nodZ, noeL and nolK genes was sufficient to permit nodulation of L. burttii, but was insufficient to induce nodulation of L. japonicus, L. corniculatus and L. filicaulis. The importance of the carbamoyl and methyl groups, and the influence of Nod factor concentration during nodulation were also implicated in this study. A model for the Nod factor perception in Lotus was proposed.
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Kiers, Erica Tobyn. "Evolution of cooperation in the legume-rhizobium symbiosis /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
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Sumpton, David. "Mass Spectrometric Studies Of The Rhizobium-Legume Symbiosis." Thesis, University of York, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485143.
Full textAbstract:
The highly specific symbiotic interaction between leguminous plants and rhizobial bacteria culminates in the fixation of atmospheric nitrogen which is made available to the host plant and ultimately replenishes the soil. This has the potential to act as a natural means to the benefits now frequently derived through the use of fertilizers Within agriculture. We have been investigating this symbiosis for soybean cultivars cropped in China, where the level of soluble nitrogen often limits crop yields. Through the use of classic carbohydrate isolation methodologies and' state-of-the-art mass spectrometric approaches, the profiling and structural characterisation of key glycoconjugate mediators ofthe symbiosis was performed. The LPS profile fromMesorhizobium tianshanenese, a rhizobium strain which has surprising symbiotic properties, was established and compared to the LPS profiles of other strains of rhizobia. The isolation and the structural characterisation of the capsular polysaccharide from 'the efficient soybean nodulator S. fredii SMHI2, was attempted. It was shown that SMH12 does not produce KPS which resembles any of the other previously identified rhizobial KPSs. The capsular polysaccharide of a Sinorhizobium fredii HH103 mutant (HH103rif ) was also successfully isolated and its structure was shown to be identical to that ofthe HHI03 strain. The structures of the periplasmic and secreted forms ofthe ~-cycloglucan from S. fredii HHI03 were characterised. The degree of polymerisation of the secreted form was found to vary between GlcI8 and Glc26 glucose residues. The periplasmic form was found to vary between 21 and 23 glucoses, and was substituted with three phosphoglycerol moieties. The structures of the major Nod Factor species secreted from two Mesorhizobium loti nod gene mutants (nodZ, nolL) which had shown phenotypic variation in their nodulation behavior, were profiled. Through the analysis ofanother nod mutant ofm. loti, the minimum nodgenes required forM loti to be able to nodulate L. japonicus were identified, namely nodDI, nodD2, nodA and node. Modifications to the structure of rhizobial membrane lipids can significantly compromise the successful outcome of the symbiosis. The /px02 gene is involved in .the synthesis of lipids in Burkholderia cenocepacia and is thought to be important for pathogenesis. In order to investigate the activity of the B. cenocepacia lpx02 gene, the extractable lipids of B. enocepacia and a B. cenocepacia mutant in which extra copies of the lpx02 gene had been introduced were identified using mass spectrometry. The study focused on identifying the site of lipid hydroxylation catalysed by the Ipx02 gene product. The structures of a range of lipid classes (pG, CL, PE, PE-OR, OL, and OL-OR) were profiled in both the wild type and mutant strain. Introduction of extra copies of lpx02 into B. cenocepacia resuIt~d in two additional lipid species, the first of which was consistent with a hydroxylated ornithine lipid structure, hydroxylation being on the amide linked acyl chain. The second species was hydroxylated, on both fatty acid residues. These results suggest that the lpx02 gene is capable of hydroxylating both ornithine lipids and hydroxylated ornithine lipids. Several targeted studies ofthe proteomes ofthe two symbiotic partners were undertaken. Due to the inherent problems associated with plant proteomics, especially the recalcitrant nature of the sample, alternative monolithic LC-MS/MS based methods were developed that allowed the successful analysis of selected sub-proteomes, where classical approaches failed. These approaches were evaluated through the analysis of several different protein mixtures ranging in complexity and generated during the study of the rhizobium-legume symbiosis. These enabled the identification of two new proteins secreted via a type III secretion mechanism, by the beneficial soybean nitrogen fixing micro-symbiont S.fredii HHI03.
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Huyop, Fahrul Zaman. "Analysis of Rhizobium sp. dehalogenases and their regulation." Thesis, University of Leicester, 2001. http://hdl.handle.net/2381/29661.
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The genus of the organism was confirmed as Rhizobium by partial sequencing of its 16S rRNA gene. The Rhizobium sp. DehL, DehE and DehD were produced by heterologous expression of the cloned genes in Escherichia coli K-12 and the proteins purified. All three dehalogenases were further characterised by kinetic analysis. The Km, Kcat and the Specificity Constants of these enzymes were determined. Rhizobium sp. was able to grow at 0.2mM 2,2DCP, which were 100x lower than the concentration of the substrate routinely used. Apparently, no new dehalogenases are required to allow growth on this low concentration of 2,2DCP as judged by electrophoretic mobility of dehalogenase proteins on Native-PAGE analysis and protein separation by anion-exchange column chromatography. The kinetic analysis suggested that the known dehalogenases were able to act efficiently on low concentrations of haloalkanoic acids. The amount of each dehalogenase, from cells grown on low substrate concentration was different to that seen at 20mM 2,2DCP due to complex regulatory controls, which respond to the growth environment. The cloning of the putative Rhizobium sp. regulator gene was achieved using phenotypic co-selection and the deduced amino acid sequence was compared to the databases. The putative regulatory sequence of Rhizobium sp. was highly homologous to the DehR1 of Pseudomonas putida PP3 with a sequence identify of 72% and the DhlR of Xanthobacter autotrophicus GJ10 with 48% identity. The regulatory gene was cloned into a high expression vector but the protein produced was found in inclusion bodies and presumably not active.
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Gagnon, Hubert. "Molecular signalling in Lupinus albus-Rhizobium lupini symbiosis." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0005/NQ40296.pdf.
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Gray, Kathryn Margaret. "Regulation of oxidative stress responses of rhizobium leguminosarum." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408404.
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Luca, Nicola de. "The regulation of iron acquisition in Rhizobium leguminosarum." Thesis, University of East Anglia, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267474.
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Krehenbrink, Martin. "Protein secretion in Rhizobium leguminosarum biovar viciae 3841." Thesis, University of East Anglia, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432434.
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Hawkins, Fiona K. L. "Studies on the nifA gene of Rhizobium leguminosarum." Thesis, University of East Anglia, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329054.
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Wilkinson, Adam. "N-acyl-homoserine lactone signalling in Rhizobium leguminosarum." Thesis, University of East Anglia, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267721.
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White, James. "Amino acid transport and metalobism by Rhizobium leguminosarum." Thesis, University of Reading, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.440075.
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Fry, Judith. "myo-Inositol utilisation by Rhizobium leguminosarum biovar viciae." Thesis, University of Reading, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326187.
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Issa, Salaheddine Issa. "Survival and movement of Rhizobium in dry soil." Thesis, University of Reading, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278037.
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Hood, Graham. "Physiological response of Rhizobium leguminosarum during bacteroid development." Thesis, University of East Anglia, 2013. https://ueaeprints.uea.ac.uk/48693/.
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legume-rhizobia symbioses, free-living rhizobia colonise root nodules and develop into N2 fixing specialists known as bacteroids. During bacteroid development, rhizobia must adapt to the nodule environment, consisting of reactive oxygen species, low oxygen, antimicrobial secondary metabolites, low pH and in some nodules, antimicrobial peptides. This study offers a holistic insight into the processes required by R. leguminosarum during bacteroid development in nodules formed on four legumes: Pisum sativum, Vicia faba, Vicia hirsuta and Phaseolus vulgaris. Initially, a high-throughput mutagenesis strategy was used to target genes upregulated during bacteroid development. Screening forty-two mutants on P. sativum identified some moderate phenotypes but more importantly, highlighted functional redundancy between certain gene products. A clear example of functional redundancy was seen between the Mn2+ transporters SitABCD and MntH. Single mutations in sitA or mntH did not cause a symbiotic phenotype whereas the double mutant could not form bacteroids on P. sativum, V. faba or V. hirsuta. Intriguingly, no symbiotic phenotype for the double mutant was observed on P. vulgaris. In addition to Mn2+ transporters, a Mg2+ channel, MgtE, that is essential for growth in Mg2+-limited medium at low pH was identified. As with the Mn2+ transporters, the requirement of MgtE during symbiosis depended upon the species of the hostlegume. Reasons for host-dependent requirement of SitABCD, MntH and MgtE are discussed. The requirement of three O2-responsive regulators that govern regulatory pathways essential to N2 fixation was also investigated. FnrN appears to be the major O2- responsive regulator required for symbiosis but in addition to fnrN, two genes, fixL and fixLc, need to be mutated to prohibit N2 fixation. Other findings include a putative toxin-antitoxin system that hinders N2 fixation when disturbed.
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Cairns, Stephen Scott. "The cloning and analysis of Rhizobium dehalogenase genes." Thesis, University of Leicester, 1994. http://hdl.handle.net/2381/35190.
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A Rhizobium genomic library was constructed in Escherichia coli NM522 and the library was screened for the ability to grow on the halogenated compound 2-chloropropionate (2CP). Two positive clones were identified and the plasmids designated pSC1 and pSC530. Both clones allowed E. coli to grow on 2CP at growth rates slower than that seen for the Rhizobium. Investigation of the dehalogenase activities of the clones showed that extracts from cells containing pSC1 were active against D-, L- and D/L-2CP and extracts from cells containing pSC530 were also active against dichloropropionate. Restriction enzyme mapping of the clones indicated that they were unique regions of the genome that conferred the new growth ability on E. coli. Southern analysis of the Rhizobium genomic DNA using insert DNA as probes confirmed that both of the clones were from the Rhizobium and that the clones were not contiguous on the genome. Subcloning of pSC1 resulted showed that the insert encoded two stereospecific dehalogenase genes and two plasmids were constructed by subcloning that were each able to express each of the two dehalogenases. The stereospecific dehalogenases (HadD and HadL) were purified and the N-terminal amino acid sequences were determined. HadL was also purified from the Rhizobium and the N-terminal sequence was shown to be the same as the cloned HadL. The complete nucleotide sequences of the hadD and hadL genes were determined and showed little similarity to each other or to other known dehalogenases. HadD and HadL were used, both in vivo and in vitro, to resolve a racemic solution of 2CP, an analagous situation to possible industrial applications of dehalogenases.
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Ouahal, Mohamed. "Étude de l'activité de restriction chez Rhizobium meliloti." Lille 1, 1985. http://www.theses.fr/1985LIL10114.
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Mazurier, Sylvie. "Diversité de populations naturelles nodulantes de Rhizobium leguminosarum." Lyon 1, 1989. http://www.theses.fr/1989LYO10067.
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L'etude d'une population naturelle de r. Leguminosarum a porte deux annees de suite sur quatre ensembles de bacteries nodulant des especes vegetales differentes cultivees dans un meme champ dans des conditions experimentales choisies pour permettre l'etude du biovar phaseoli (haricot), biovar trifolii (trefle) et de deux echantillons du biovar viceae (pois et lentille) en estimant l'influence de facteurs de milieu sur la diversite de ces populations; genotype vegetal, espace, temps et historique cultural. L'analyse des profils plasmidiques d'une centaine d'isolats de chacun de ces ensembles a montre que les rhizobium peuvent etre regroupes en types de similarite totale ou en classes definies par la presence de quelques plasmides communs, le plus souvent cryptiques. Des similitudes entre profils de restriction d'adn total ou isoenzymatiques des isolats ainsi regroupes revelent des caracteristiques chromosomiques communes. Ces resultats permettent, en outre, de rapprocher des isolats de biovars differents. La diversite estimee par le nombre de profils differents et les dominances de classes plasmidiques varient selon les ensembles etudies. Les isolats de ces ensembles possedent egalement des capacites variables a fixer l'azote en symbiose: les rhizobium nodulant le trefle et le pois sont fixateurs alors que le cinquieme, pour la lentille, et la moitie, pour le haricot, sont inefficients. Certaines classes plasmidiques permettent de regrouper des isolats de capacites fixatrices homogenes. Ce niveau de caracterisation est ainsi valide. En comparant les differents ensembles etudies, le genotype vegetal apparait comme un facteur determinant l'expression de la diversite microbienne lors de la mise en place d'une population nodulante et en tant que culture specifique precedant un isolement. Le facteur temps ne semble pas modifier la diversite decrite. Concernant le facteur espace, cette diversite est du meme
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Galiana, Antoine. "La symbiose fixatrice d'azote chez acacia mangium - rhizobium." Paris 6, 1990. http://www.theses.fr/1990PA066516.
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Quarante deux souches de rhizobium ont ete isolees de nodules d'acacia mangium recoltes dans l'aire d'origine (australie) et dans diverses zones d'introduction de l'espece. La caracterisation de ces souches a montre qu'elles appartenaient toutes au genre bradyrhizobium. Les souches originaires d'australie presentent une effectivite superieure aux souches d'autres origines ou aux souches de collection isolees chez d'autres especes. Nous avons tente d'etablir une relation entre les quantites d'aia et de cytokinines produites par trois souches (aust 13c, tal 72, ors 800) ex-plants et celles contenues dans les nodules formes par ces souches. Les nodules formes par la souche aust 13c ont une teneur en zr, ip et ipa deux a trois fois plus elevee que ceux formes par les autres souches. Ceci pourrait etre lie a une activite meristematique et une activite fixatrice d'azote prolongees de ces nodules. La troisieme partie de notre etude concerne l'amelioration de la fixation de l'azote par selection clonale d'a. Mangium. Apres la mise au point d'une technique de micropropagation conforme (stimulation du bourgeonnement axillaire de jeunes explants de tiges), cinq clones ont pu etre selectionnes a un stade precoce en fonction de leur potentiel fixateur d'azote. L'inoculation de cinq clones avec trois souches de bradyrhizobium sp. D'effectivites variables montre que: (1) le potentiel fixateur d'azote des clones est conserve quelle que soit la souche testee; (2) l'effectivite des trois souches varie dans le meme sens quel que soit le clone considere. L'effet de l'interaction souche x clone n'etant pas significatif, les partenaires de la symbiose peuvent etre selectionnes separement. Les essais d'inoculation d'a. Mangium au champ sur differents types de sol (benin, iles cook et cote d'ivoire) ont montre un effet positif de l'inoculation sur la nodulation et la croissance des plants plus d'un an pres transplantation au champ. Ils ont egalement confirme l'effectivite superieure des souches d'a. Mangium d'origine australienne par rapport aux autres souches testees
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Donaldson, Pauline A. (Pauline Alison) Carleton University Dissertation Biology. "Nodulation and tumorgenesis by Agrobacterium carrying Rhizobium plasmids." Ottawa, 1985.
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Reeve, Wayne. "The molecular basis of acid-tolerance in Rhizobium." Thesis, Reeve, Wayne (1995) The molecular basis of acid-tolerance in Rhizobium. PhD thesis, Murdoch University, 1995. https://researchrepository.murdoch.edu.au/id/eprint/41087/.
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The aim of this study was to investigate the molecular basis of acidtolerance in Rhizobium. Transposon Tn5-induced mutants were used to identify genes required for acid-tolerance in the Sardinian strain Rhizobium meliloti WSM419 and the Japanese strainR. leguminosarum bv. viceae WSM710. Plant inoculation tests showed that nodulation by these acid-sensitive mutants on their respective hosts was comparable to that of the wild-type.
Calcium affected the growth of both wild-type Rhizobium strains at acidic pH. Cells of R. meliloti WSM419 grew faster at acidic pH and could grow at a progressively lower pH as the calcium concentration was increased. R.
leguminosarum WSM710 was able to grow below pH 4.9 if the concentration of calcium was increased in the medium. The acid-sensitive mutants could be divided into two groups on the basis of their response at acidic pH to the external calcium concentration. The first group (R. meliloti strains TG 1-6, TG 1-11, TG2-6, TGS-46 and R. leguminosarum WR6-35) grew at low pH if extra calcium was supplied in the medium. In the second group were those mutants (R. meliloti RT3-27 and R. leguminosarum WRl-14) that were unable to grow at low pH even if a high concentration of calcium was supplied.
Southern hybridisation studies using Tn5 as a probe demonstrated that each mutant contained only a single copy of Tn5. The re-insertion of Tn5 back into the wild-type using a suitable site-directed homologous recombination strategy (with an appropriate suicide vehicle for R. meliloti or phage RL38 mediated transduction for R. leguminosarum) recreated the acid-sensitive phenotype which verified that Tn5 was the causative agent of the disruption of a gene required for acid-tolerance.
The rhizobial DNA flanking Tn5 was cloned from the mutants TG2-6, TGS-46, RT3-27, WR6-35, and WRl-14 and the DNA was sequenced and analysed for protein encoding regions. DNA or protein sequences were then used to search for similarity in the GenBank, EMBL, or GenPeptide databases. The genes interrupted by Tn5 in the mutants were designated as act genes (acidtolerance genes) and numbered according to the name of the mutant; for example, the gene disrupted by Tn5 in TG2-6 was labelled as act206.
The predicted protein (Act206) encoded by act206 in WSM419 is 541 amino acids in length and has an estimated molecular weight of 57, 963 D and a pl of 9.0. An incomplete open reading frame contiguous to act206 appears to code for a DNA binding protein homologous to URF4 of Rhodospirillum rubrum and n~pressors in coliphage. The Act206 protein has a small degree of identity (30 % over 465 amino acids) but higher similarity (69 % over 465 amino acids) to CutE from Escherichia coli. Disruption of the latter protein caused a copper sensitive phenotype in cells of E. coli. S. typhimurium also contains an allele of cutE which, if mutated, causes a temperature-sensitive and copper-sensitive phenotype and a reduction in the activity of the lipid metabolising enzyme apolipoprotein Nacy ltransferase. The act206 mRNA was found in cells grown under both acidic (pH 5.8) and neutral (pH 7.0) conditions. The act206 gene appears to be chromosomal and was found in all seven strains of R. meliloti examined. At this stage the role of Act206 in acid-tolerance remains unclear.
The gene inactivated in WR6-35 has a strong similarity to the exoR sequence of R. meliloti Rm1021 (71.3 % over 892 bp). The protein (Act635) encoded by act635 is predicted to be 267 amino acids in length with a molecular weight of 28, 920 D and a calculated pl of 5.5. The Act635 protein has 93.3 % similarity and 70 % identity over 267 amino acids with R. meliloti Rm1021 ExoR. Strain WR6-35 produced approximately twice as much EPS as the wild-type WSM710 under the conditions used. NMR spectra of EPS produced by the wildtype and WR6-35 were indistinguishable. Disruption of exoR in R. leguminosarum caused a mildly acid-sensitive phenotype; one possible explanation is that a perturbation of the cytoplasmic membrane has resulted through an overproduction of EPS which subsequently caused an increased susceptibility to proton influx. The gene disrupted by Tn5 in R. meliloti TG5-46 (actR; previously called act546) encodes a protein (ActR) of 193 amino acids with a predicted molecular weight of 21, 463 D and a pl of 8.3. This protein has a similar amino-terminal region to regulatory proteins of the histidine protein kinase/regulator protein family involved in signal transduction in bacteria. ActR has a high degree of similarity over the entire protein sequence of PrrA from Rhodobacter capsulatus (94.9 % similarity, 69.3 % identity over 176 amino acids). It also had a high degree of similarity with RegA from Rhodobacter capsulatus (92.6 % similarity, 70.5 % identity over 176 amino acids) or R. sphaeroides (92.6 % similarity, 67.0 % identity over 176 amino acids). Neither, PrrA or RegA belong to any recognised subclass ofregulators and hence have been classified in a new subgroup. It is postulated that ActR falls into this new subgroup based on protein similarity. The predicted protein encoded by the gene upstream to actR showed similarity with sensor proteins, such as PhoR (67.2 % similarity and 24.6 % identity over 244 amino acids) from Escherichia coli and FixL (69.5 % similarity and 25.4 % identity over 256 amino acids) from Bradyrhizobium japonicum, which are members of the histidine protein kinase/regulator family. It is speculated that this protein, consequently labelled as ActS, may play a role in the detection of the hydrogen ion concentration and transfer this signal to ActR which in turn regulates one or more structural genes.
The genes inactivated in R. meliloti RT3-27 (act327) or R. leguminosarum WRl-14 (actl 14) showed similarity with genes which encode P-type ATPases in a variety of eukaryotes and prokaryotes. These genes may encode proteins which have a direct role in proton translocation or an indirect role through ion transport in the cell.
The possible implications of these findings are discussed and a tentative model for the genetic basis of acid-tolerance in Rhizobium is presented.
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Carson, Kerry C. A. "Iron nutrition of Rhizobium leguminosarum biovar viciae MNF710." Thesis, Carson, Kerry C.A. (1993) Iron nutrition of Rhizobium leguminosarum biovar viciae MNF710. PhD thesis, Murdoch University, 1993. https://researchrepository.murdoch.edu.au/id/eprint/51953/.
Full textAbstract:
This thesis reports investigations into the iron nutrition and metabolism of Rhizobium leguminosarum biovar viciae MNF710; this organism excretes a trihydroxamate siderophore which I have named hydroxamate K This is the first report of a trihydroxamate siderophore produced by root nodule bacteria.
Using transposon Tn5 mutagenesis, three mutants of MNF 710were isolated, two of which proved useful. Mutant MNF7101 excretes a variety of hydroxamate siderophores but not hydroxamate K The major product is a trihydroxamate chemical different from hydroxamate K but still structurally similar.
Hydroxamate K is a trihydroxamic acid, which appears to consist of three molecules each of N5-hydroxyornithine and 3-hydroxybutyrate, joined together by alternating peptide and ester linkages. The N5-hydroxyornithine is also acetylated to produce the hydroxamic acid groups involved in iron chelation. The major trihydroxamate siderophore produced by mutant MNF7101 carries a positive charge and lacks the acetyl groups found in hydroxamate K MNF7101 therefore appears to lack a specific acetylase activity required for the acetylation of N5 - hydroxyornithine in MNF710.
Mutant MNF7102 does not produce hydroxamate K or any other siderophore, but can still transport 55Fe complexed with it. This mutant appears to be defective in either the induction of hydroxamate K biosynthesis, or in a vital biosynthtic gene.
Iron deficiency in MNF710 induces the production of three iron-repressible outer membrane proteins (IROMPs) which are probably receptors for iron- siderophore complexes. Cells of MNF710 can transport 55Fe complexed to hydroxamate K, ferrioxamine B, ferrichrome, ferrichrome A, rhodotorulate, citrate and nitrilotriacetic acid (NTA). MNF7102 will also transport these iron-siderophore complexes. Neither MNF710 nor MNF7102 will transport 55Fe complexes to enterobactin or to the pyoverdines from Pseudomonas aeruginosa ATCC15692 or ATCC17400.
In R. leguminosarum MNF710 all of these transport systems are ironregulated, but in MNF7102 iron transport mediated by rhodotorulate, citrate and NTA is constitutive.
Other root nodule bacteria, like Rhizobium leguminosarum biovar trifolii WU95 and Rhizobium meliloti U45, also transport 55Fe complexed to siderophores they do not produce. In some instances these transport systems are iron-repressible (hydroxamate K, ferrioxamine B and ferrichrome transport in WU95) and in others they are constitutive (rhodotorulate, citrate and NTA transport in both WU95 and U45, and ferrichrome and ferrichrome A transport in U45).
When grown with a high iron concentration, R. leguminosarum MNF710 appears to accumulate iron in the form of a bacterioferritin and other iron storage proteins identifiable by Mossbauer spectroscopy. While this is the first indication of iron storage proteins in root nodule bacteria, the roles these may play in the regulation of iron metabolism within the cells are unknown.
Biosynthesis of hydroxamate K is iron-regulated, with excretion occurring only when cells of R. leguminosarum MNF710 are iron-stressed. However, induction of the biosynthetic genes for hydroxamate K appears to be influenced by some form of stored iron within the cells. A model has been developed in which hydroxamate K production is controlled by an "immediately available" form of iron which is in dynamic equilibrium with the storage iron. Regardless of the external iron concentration it appears that the iron concentration within the cell must be maintained above a critical level; if not, siderophore synthesis is derepressed and continues until the stored iron concentration is restored.
The significant finding from this work is that the free-living form of R. leguminosamm MNF710 has the potential to use three different strategies to ensure survival and growth under iron-deficient conditions - specific siderophore production and uptake, utilization of siderophores produced by other microorganisms, and short-term iron storage for later growth.