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1
Landrum, Jason Paul. "Movement of new nitrogen through oceanic food webs." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28151.
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Thesis (M. S.)--Biology, Georgia Institute of Technology, 2009.Committee Chair: Joseph Montoya; Committee Member: Ellery Ingall; Committee Member: Emanuele DiLorenzo; Committee Member: Marc Weissburg; Committee Member: Mark Hay.
2
Terpolilli, Jason James. "Why are the symbioses between some genotypes of Sinorhizobium and Medicago suboptimal for N₂ fixation? /." Murdoch University Theses Program, 2009. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20090727.143325.
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Lennihan, Robert. "Ecology of Nostoc in a high arctic oasis /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/5184.
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Rapley, Joanne. "Phylogenetic diversity of nifH genes in Marion Island soil." Thesis, University of the Western Cape, 2006. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_1001_1223535337.
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The microbial life of sub-Antarctic islands plays a key role in the islands ecosystem, with microbial activities providing the majority of nutrients available for primary production. Knowledge of microbial diversity is still in its infancy and this is particularly true regarding the diversity of micro-organisms in the Antarctic and sub-Antarctic regions. One particularly important functional group of micro-organisms is the diazotrophs, or nitrogen-fixing bacteria and archaea. This group have not been well studied in the sub-Antarctic region, but play an important role in the nutrient cycling of the island. This thesis explored the diversity of nitrogen-fixing organisms in the soil of different ecological habitats on the sub-Antarctic Marion Island.
5
Bunch, Nathan D. "Microbial response to nitrogen availability : preferential and adaptive community uptake." CardinalScholar 1.0, 2010. http://liblink.bsu.edu/uhtbin/catkey/1562868.
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This project was designed to assess the ability of natural sediment microbial communities and single species microbial populations to preferentially utilize inorganic forms of nitrogen (ammonium, NH4-N, and nitrate, NO3-N, specifically). The first chapter addressed two primary questions: 1) Do sediment microbial communities preferentially assimilate NH4-N or NO3-N?; and, 2) Does preferential uptake of nitrogen change with increased NH4-N or NO3-N availability? The second chapter furthered these analyses by assessing shifts in microbial nitrogen assimilation in response to sustained nitrogen enrichments. Primary questions addressed were: 1) Are microbial communities able to adapt to nitrogen enrichment and preferentially utilize a more available source?; and, 2) Are initial microbial responses to nitrogen enrichment different from sustained responses? Questions were addressed with in vitro laboratory experiments quantifying microbial activity. Overall, microbial community activity changed in response to the form of nitrogen available, enrichment type, and duration of exposure. Data demonstrate sediment microbial communities in the Midwestern US may prefer NO3-N over other forms of nitrogen. However, microbial communities became saturated with NO3-N with increases in concentrations >0.75 mg NO3-N/L. Microbial communities were able to adapt to higher nitrogen concentration and increase rates of assimilation for both NH4-N and NO3-N. Thus, microbial communities are robust in response to nitrogen increases in and ecosystem, even in high nitrogen environments like the Midwestern US.Preferential uptake of available nitrogen forms -- Adaptive uptake in microbial communities.
Department of Biology
6
Xin, Gang. "Diazotrophic endophytes of Populus /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/10104.
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Lynch, Derek H. (Derek Henry). "Low root-zone temperatures and soybean (Glycine max (L.) Merr.) N2- fixing symbiosis development." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56677.
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This research tested the hypotheses that (a) suboptimal root-zone temperatures (RZT) limit the soybean-Bradyrhizobium N$ sb2$-fixing symbiosis primarily through an inhibition of symbiosis establishment and (b) this inhibition is modified by the genotype of micro- or macrosymbiont. Controlled environment and field experiments were conducted utilizing two soybean genotypes and six B. japonicum strains. At 19$ sp circ$C RZT fixed nitrogen levels decreased by 30-40%, predominantly due to a restriction in the latter stages of nodule development. Reductions of 10% and 30% in specific nodule activity rates at 19$ sp circ$C and 15$ sp circ$C RZT respectively, indicated nodule function to be comparatively insensitive to low RZT. Soybean genotypes did not differ in seedling nodulation or N$ sb2$-fixation under cool-soil, field or controlled environment, conditions. At all temperatures, commercial B. japonicum strain 532C was more efficient, but not effective, than strains obtained from the cool-soils of Northern Japan. Under cool-soil field conditions, two of the latter strains increased seedling nodulation and N$ sb2$-fixation.
8
Nandasena, Kemanthi Gayathri. "Rapid evolution of diversity in the root nodule bacteria Biserrula plecinus L." Thesis, Nandasena, Kemanthi Gayathri (2004) Rapid evolution of diversity in the root nodule bacteria Biserrula plecinus L. PhD thesis, Murdoch University, 2004. https://researchrepository.murdoch.edu.au/id/eprint/221/.
Full textAbstract:
Biserrula pelecinus L. has been introduced to Australia from the Mediterranean region, in the last decade due to many attractive agronomic features. This deep rooted, hard seeded, acid tolerant and insect resistant legume species provides high quality food for cattle and sheep, and grows well under the harsh edaphic and environmental conditions of Australia. In 1994, B. pelecinus was introduced to a site in Northam, Western Australia where there were no native rhizobia capable of nodulating this legume. The introduced plants were inoculated with a single inoculant strain of Mesorhizobium sp., WSM1271. This study investigated whether a diversity of rhizobia emerged over time. A second objective was to investigate the possible mechanisms involved in the diversification of rhizobia able to nodulate B. pelecinus.
Eighty eight isolates of rhizobia were obtained from nodules on B. pelecinus growing at the Northam site in August 2000, six years after introduction. These plants were self-regenerating offspring from the original seeds sown. Molecular fingerprinting PCR with RPO1 and ERIC primers revealed that seven strains (novel isolates) had banding patterns distinct from WSM1271 while 81 strains had similar banding patterns to WSM1271. A 1400 bp internal fragment of the 16S rRNA gene was amplified and sequenced for four of the novel isolates (N17, N18, N45 and N87) and WSM1271. The phylogenetic tree developed using these sequences clustered the novel isolates in Mesorhizobium. There were >6 nucleotide mismatches between three of the novel isolates (N17, N18, N87) and WSM1271 while there were 23 nucleotide mismatches between N45 and WSM1271.
When B. pelecinus cv. Casbah was inoculated with the novel isolates, five (N17, N18, N39, N46 and N87) yielded <40% of the shoot dry weight of the plants inoculated with the original inoculant (WSM1271). Novel isolates N15 and N45 were completely ineffective on B. pelecinus cv. Casbah.
Physiological experiments to test the ability of the novel isolates and WSM1271 to grow on 14 different carbon sources (N acetyl glucosamine, arabinose, arbutine, dulcitol, beta-gentiobiose, lactose, maltose, melibiose, D-raffinose, saccharose, L-sorbose, D-tagatose, trehalose and D-turanose) as the sole source of carbon, intrinsic resistance to eight different antibiotics (ampicillin, chloramphenicol, gentamicin, kanamycin, nalidixic acid, spectinomycin, streptomycin and tetracycline) and pH tolerance (pH 4.5, 5.0, 7.0, 9.0) revealed that the novel isolates had significantly different carbon source utilization patterns to WSM1271. However, pH tolerance and intrinsic resistance to antibiotics were similar between the novel isolates and WSM1271 except for streptomycin (100 mcg/ml). Novel isolates N17, N18, N46 and N87 were susceptible for this antibiotic while the other novel isolates and WSM1271 were resistant.
Host range experiments were performed for the novel isolates N17, N18, N45, N87, WSM1271 and two other root nodule bacteria (RNB) previously isolated from B. pelecinus growing in the Mediterranean region (WSM1284 and WSM1497) for twenty one legumes (Amorpha fruticosa, Astragalus adsurgens, Astragalus membranaceus, Astragalus sinicus, Biserrula pelecinus cv Casbah, Dorycnium hirsutum, Dorycnium rectum, Glycyrrhiza uralensis, Hedysarum spinosissimum, Leucaena leucocephala, Lotus corniculatus, Lotus edulis, Lotus glaber, Lotus maroccanus, Lotus ornithopodioides, Lotus parviflorus, Lotus pedunculatus, Lotus peregrinus, Lotus subbiflorus, Macroptilium atropurpureum, and Ornithopus sativus). Only isolate N17 have the same host range as WSM1271 in that they both nodulated B. pelecinus and A. membranaceus, while the other three novel isolates, WSM1284 and WSM1497 had a broader host range than WSM1271. Three isolates N18, N45 and N87 formed small white nodules on M. atropurpureum, in addition to nodulating the above hosts. Isolates N18 and N45 also nodulated A. adsurgens while N45 was the only isolate to nodulate L. edulis. Isolate N87 was the only isolate to nodulate A. fruticosa. WSM1497 nodulated A. adsurgens, A. membranaceus, B. pelecinus and L. corniculatus while WSM1284 was a promiscuous strain that nodulated 16 host species out of the 21 tested. A 710 bp internal region of nifH, a 567 bp internal region of nodA and a 1044 bp internal region of intS were sequenced for N17, N18, N45, N87 and WSM1271. The sequence comparison showed that the sequences of the above three genes of the four novel isolates were identical to that of WSM1271.
Eckhardt gel electrophoresis revealed that WSM1271, three other RNB isolates from B. pelecinus from the Mediterranean region and isolate N18 each have a plasmid of approximately 500 kb while N17, N45 and N87 are plasmid free. Probing of the plasmid DNA from the Eckhardt gel with nifH and nodA probes indicated that these two genes were not located on the plasmid.
Furthermore, the results of this study demonstrated that 92% of the nodules on B. pelecinus growing in the Northam site six years after the introduction of this plant were occupied by the inoculant strain and the N2 fixation efficiency of the progeny strains of WSM1271 remain similar to the mother culture. This study also showed that the carbon source utilization pattern, intrinsic antibiotic resistance and pH range of the progeny strains of WSM1271 remain relatively similar, except for few variations in carbon source utilization patterns.
This thesis clearly demonstrated that phenotypicaly, genetically and phylogenetically diverse strains capable nodulating B. pelecinus evolved through symbiotic gene transfer from the inoculant strain to other soil bacteria within six years. The presence of intS, and the evidence of gene transfer between these Mesorhizobium strains indicates that transfer of symbiotic genes may have occurred via a symbiosis island present in WSM1271.
9
Nandasena, Kemanthi Gayathri. "Rapid evolution of diversity in the root nodule bacteria Biserrula plecinus L." Nandasena, Kemanthi Gayathri (2004) Rapid evolution of diversity in the root nodule bacteria Biserrula plecinus L. PhD thesis, Murdoch University, 2004. http://researchrepository.murdoch.edu.au/221/.
Full textAbstract:
Biserrula pelecinus L. has been introduced to Australia from the Mediterranean region, in the last decade due to many attractive agronomic features. This deep rooted, hard seeded, acid tolerant and insect resistant legume species provides high quality food for cattle and sheep, and grows well under the harsh edaphic and environmental conditions of Australia. In 1994, B. pelecinus was introduced to a site in Northam, Western Australia where there were no native rhizobia capable of nodulating this legume. The introduced plants were inoculated with a single inoculant strain of Mesorhizobium sp., WSM1271. This study investigated whether a diversity of rhizobia emerged over time. A second objective was to investigate the possible mechanisms involved in the diversification of rhizobia able to nodulate B. pelecinus.
Eighty eight isolates of rhizobia were obtained from nodules on B. pelecinus growing at the Northam site in August 2000, six years after introduction. These plants were self-regenerating offspring from the original seeds sown. Molecular fingerprinting PCR with RPO1 and ERIC primers revealed that seven strains (novel isolates) had banding patterns distinct from WSM1271 while 81 strains had similar banding patterns to WSM1271. A 1400 bp internal fragment of the 16S rRNA gene was amplified and sequenced for four of the novel isolates (N17, N18, N45 and N87) and WSM1271. The phylogenetic tree developed using these sequences clustered the novel isolates in Mesorhizobium. There were >6 nucleotide mismatches between three of the novel isolates (N17, N18, N87) and WSM1271 while there were 23 nucleotide mismatches between N45 and WSM1271.
When B. pelecinus cv. Casbah was inoculated with the novel isolates, five (N17, N18, N39, N46 and N87) yielded <40% of the shoot dry weight of the plants inoculated with the original inoculant (WSM1271). Novel isolates N15 and N45 were completely ineffective on B. pelecinus cv. Casbah.
Physiological experiments to test the ability of the novel isolates and WSM1271 to grow on 14 different carbon sources (N acetyl glucosamine, arabinose, arbutine, dulcitol, beta-gentiobiose, lactose, maltose, melibiose, D-raffinose, saccharose, L-sorbose, D-tagatose, trehalose and D-turanose) as the sole source of carbon, intrinsic resistance to eight different antibiotics (ampicillin, chloramphenicol, gentamicin, kanamycin, nalidixic acid, spectinomycin, streptomycin and tetracycline) and pH tolerance (pH 4.5, 5.0, 7.0, 9.0) revealed that the novel isolates had significantly different carbon source utilization patterns to WSM1271. However, pH tolerance and intrinsic resistance to antibiotics were similar between the novel isolates and WSM1271 except for streptomycin (100 mcg/ml). Novel isolates N17, N18, N46 and N87 were susceptible for this antibiotic while the other novel isolates and WSM1271 were resistant.
Host range experiments were performed for the novel isolates N17, N18, N45, N87, WSM1271 and two other root nodule bacteria (RNB) previously isolated from B. pelecinus growing in the Mediterranean region (WSM1284 and WSM1497) for twenty one legumes (Amorpha fruticosa, Astragalus adsurgens, Astragalus membranaceus, Astragalus sinicus, Biserrula pelecinus cv Casbah, Dorycnium hirsutum, Dorycnium rectum, Glycyrrhiza uralensis, Hedysarum spinosissimum, Leucaena leucocephala, Lotus corniculatus, Lotus edulis, Lotus glaber, Lotus maroccanus, Lotus ornithopodioides, Lotus parviflorus, Lotus pedunculatus, Lotus peregrinus, Lotus subbiflorus, Macroptilium atropurpureum, and Ornithopus sativus). Only isolate N17 have the same host range as WSM1271 in that they both nodulated B. pelecinus and A. membranaceus, while the other three novel isolates, WSM1284 and WSM1497 had a broader host range than WSM1271. Three isolates N18, N45 and N87 formed small white nodules on M. atropurpureum, in addition to nodulating the above hosts. Isolates N18 and N45 also nodulated A. adsurgens while N45 was the only isolate to nodulate L. edulis. Isolate N87 was the only isolate to nodulate A. fruticosa. WSM1497 nodulated A. adsurgens, A. membranaceus, B. pelecinus and L. corniculatus while WSM1284 was a promiscuous strain that nodulated 16 host species out of the 21 tested. A 710 bp internal region of nifH, a 567 bp internal region of nodA and a 1044 bp internal region of intS were sequenced for N17, N18, N45, N87 and WSM1271. The sequence comparison showed that the sequences of the above three genes of the four novel isolates were identical to that of WSM1271.
Eckhardt gel electrophoresis revealed that WSM1271, three other RNB isolates from B. pelecinus from the Mediterranean region and isolate N18 each have a plasmid of approximately 500 kb while N17, N45 and N87 are plasmid free. Probing of the plasmid DNA from the Eckhardt gel with nifH and nodA probes indicated that these two genes were not located on the plasmid.
Furthermore, the results of this study demonstrated that 92% of the nodules on B. pelecinus growing in the Northam site six years after the introduction of this plant were occupied by the inoculant strain and the N2 fixation efficiency of the progeny strains of WSM1271 remain similar to the mother culture. This study also showed that the carbon source utilization pattern, intrinsic antibiotic resistance and pH range of the progeny strains of WSM1271 remain relatively similar, except for few variations in carbon source utilization patterns.
This thesis clearly demonstrated that phenotypicaly, genetically and phylogenetically diverse strains capable nodulating B. pelecinus evolved through symbiotic gene transfer from the inoculant strain to other soil bacteria within six years. The presence of intS, and the evidence of gene transfer between these Mesorhizobium strains indicates that transfer of symbiotic genes may have occurred via a symbiosis island present in WSM1271.
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Dale, Olivia R. "Detection, diversity, and activity on anaerobic ammonium oxidizing bacteria (Anammox) in the Cape Fear River Estuary /." Electronic version (PDF), 2007. http://dl.uncw.edu/etd/2007-1/r1/daleo/oliviadale.pdf.
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Wilson, Mark Steven Michael. "Mutagenesis of nifE and nifN from Azotobacter vinelandii." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43071.
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The products of nifE and nifN from Azotobacter vinelandii, which
are involved in the biosynthesis of the iron-molybdenum cofactor (FeMo-co)
co) from nitrogenase, have been analyzed using a variety of mutagenic techniques.
NifE was the object of several site-specific, amino acid
substitutions that were designed to elicit information regarding metal cluster ligands, subunit-subunit interactions, and the proposed transfer
of FeMo-co.from a nifEN-products complex to the apo-MoFe protein. A
model of metal cluster binding; regions within the nifEN-products is
discussed insofar as it relates to the rationale for the targeting of
particular amino acids for-substitution.
A translational fusion between nifN and lacZ was constructed and
used to study the regulation of nifEN. This gene fusion was regulated
in the same manner as wild type nifN and produced a fusion protein which was enzymatically active with respect to substrates of β-galactosidase.
Results from mutant strains which carry lesions in nifH or nifA in
addition to the nifN::lacZ fusion are presented and discussed.Master of Science
12
Burgoyne, Tricia A. "Free living nitrogen-fixation in ponderosa pine/Douglas-fir forests of western Montana." Connect to this title online, 2007. http://etd.lib.umt.edu/theses/available/etd-05302007-085002/.
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Laniya, Titeki Sandra. "Isolation and characterisation of soybean (Glycine max) nodule autoregulation receptor kinase gene (GmNARK) /." [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18188.pdf.
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Brigle, Kevin Eugene. "Studies on the structure and function of various nif and nif- associated gene products encoded within the Azotobacter vinelandii nif gene cluster." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54498.
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The present study investigates the structural and functional roles of the metalloclusters present within the MoFe protein of nitrogenase from Azotobacter vinelandii. A gene replacement strategy was developed for oligonucleotide-directed mutagenesis of these proteins and the resulting biological and biochemical effects of these changes were examined. Identification of structurally important regions in the MoFe protein subunits and assignment of specific amino acid residues as potential metal cluster ligands were based upon several criteria: i. metallocluster extrusion requirements; spectroscopic properties of the MoFe protein; interspecies and intersubunit comparisons; iv. comparison of the MoFe protein subunit sequences to iron-molybdenum cofactor biosynthetic gene products. This mutagenesis strategy has permitted the construction of thirty-three mutant strains having specific amino acid substitutions within the MoFe protein subunits. Based on the diazotrophic growth characteristics and substrate reduction capabilities of these mutant strains, a model is presented in which potential metallocluster binding sites within the MoFe protein subunits are defined. In addition to analysis of the MoFe protein subunits, this site-directed mutagenesis and gene replacement strategy can be used to place specific mutations into any gene product encoded within the A. vinelandii nif gene cluster.
Finally, nucleotide sequence analysis of the regions flanking the nifEN genes revealed the presence of three nif genes (nifT, nifY, and nifX) and four open reading frames (ORF1, ORF2, ORF3, and ORF4). Two of these genes, nifX and ORF3, were shown to be under nif control and synthesis of their products elevated in response to a demand for fixed nitrogen. Mutant strains with deletions in ORF3 appeared to accumulate an excess amount of MoFe protein when compared to wild type. The ORF3 gene product has been overproduced in E. coli. This provides an important step toward characterizing the protein and elucidating the molecular basis for its control of nifDK gene expression.Ph. D.
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Sur, Saubashya. "Studies of codon usage, proteome analysis and evolution of nitrogen fixing genes in some microorganisms a bioinformatic approach." Thesis, University of North Bengal, 2010. http://hdl.handle.net/123456789/1378.
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Pan, Bo 1963. "Mineral nitrogen inhibition and signal production in soybean-B. japonicum symbiosis." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36670.
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In the N2 fixing legume symbiosis, mineral nitrogen (N) not only decreases N2 fixation, but also delays and inhibits the formation and development of nodules. The purposes of this thesis were to elucidate the role of signaling in the mineral N effects on nodulation and nitrogen fixation in soybean [Glycine max (L.) Merr.] and to attempt to find ways to overcome this inhibition. The responses of soybean plants, in terms of daidzein and genistein synthesis and exudation, to different mineral N levels were studied. Daidzein and genistein distribution patterns varied with plant organs, mineral N levels, and plant development stages. Mineral N inhibited daidzein and genistein contents and concentrations in soybean root and shoot extracts, but did not affect root daidzein and genistein excretion in the same way. In both synthesis and excretion, daidzein and genistein were not affected equally by mineral N treatments. Variability existed among soybean cultivars in the responses of root daidzein and genistein contents and concentrations to mineral N levels. The amount of daidzein and genistein excreted by soybean roots did not always correspond to the daidzein and genistein contents and concentrations inside the roots. On the Bradyrhizobium japonicum side, nod gene expression was inhibited by mineral nitrogen. Genistein was used to pre-incubate B. japonicum cells or was applied directly into the plant growing medium. The results showed that genistein manipulation increased nodule weight and nodule nitrogen fixation under greenhouse conditions, but interactions existed among soybean cultivars, genistein concentrations and nitrate levels. Similar results were found under field conditions. Soybean yield was increased on sandy-loam soil by preincubation of B. japonicum cells with genistein. Addition of genistein beginning at the onset of nitrogen fixation also improved soybean nodulation and nitrogen fixation. Soybean cultivars had different sensitivities to genistein additiOther studies also show that temperature affected genistein and daidzein content and concentration in soybean roots. The effect of temperature varied among soybean cultivars. Some PGPR strains can mitigate the negative effects of nitrate on soybean nodulation and nitrogen fixation, however, this is influenced by soybean genotype. Applying PGPR together with genistein preincubation of B. japonicum cells improved soybean nodulation and increased yield. The level of improvement varied among soybean cultivars and PGPR strains. Preincubation of B. japonicum cells with genistein improved strain competitiveness under greenhouse, but not field conditions.
Overall, these findings suggested that both plant-to-Bradyrhizobium and Bradyrhizobium-to-plant signals play important roles in the effects of mineral N on nodulation and N fixation. Signal manipulation could partially overcome the inhibitory effects of mineral N on soybean- B. japonicum N fixation symbiosis.
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Carlton, Timothy M., and n/a. "Iron and microevolution in Mesorhizobia." University of Otago. Department of Microbiology & Immunology, 2006. http://adt.otago.ac.nz./public/adt-NZDU20070215.154441.
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Genome plasticity in soil bacteria is predicted to be evolutionarily advantageous, allowing bacteria to sample genetic variation for adaptation to local soil ecology. In the field population of mesorhizobia where the symbiosis island (ICEMlSym[R7A]; an I̲ntegrative C̲onjugative E̲lement) was first identified, individual members were found to have significant chromosomal variation downstream of the phe-tRNA gene or phe-tRNA integrated ICEMlSym[R7A]. However, the nature of this genetic variation and whether it contributed to the adaptation of the indigenous mesorhizobia to their field environment were unknown.
This work focused on a nodule isolate, Mesorhizobium sp. strain R88B, a member of the indigenous mesorhizobial population that received ICEMlSym[R7A] from strain R7A. The region downstream of ICEMlSym[R7A] was sequenced, revealing three distinct regions of non-conserved DNA, totalling 34.5 kb. Integrated directly downstream of ICEMlSym[R7A] was IMEMlAdh[R88B], a 24.3-kb novel I̲ntegrative M̲obilisable E̲lement. Using a PCR-based assay, it was shown that the IMEMlAdh[R88B] integrase could excise not only IMEMlAdh[R88B], but also a dual-IMEMlAdh[R88B]/ICEMlSym[R7A] hybrid, indicating the potential mobility of IMEMlAdh[R88B], and a likely evolutionary intermediate of a novel ICE. However, a functional role for MadA, (a putative adhesin and the sole adaptive trait encoded on IMEMlAdh[R88B]) was not discovered. Southern hybridisations with the mesorhizobial population provided evidence for the existence of a novel family of IMEs in the mesorhizobia, which, by diversifying their internal sequences, provide allele-specific variation to the population.
The two other regions downstream of IMEMlAdh[R88B] possessed no obvious mobile genetic element structures, and only the region adjacent to the core-chromosome encoded ORFs with putative functions. Mutation of two of these ORFs, fhuD1 and fhuB1, identified their function as two of the four components of a ferrichrome ABC-uptake (Fhu) system. Using genetic screens, the remaining components of this transporter were mapped to two separate loci. Thus, the functional transporter in R88B was a composite of at least two independently-acquired Fhu systems. The genetic screens also revealed that ferrichrome utilisation was dependent on a TonB energy-transduction system encoded downstream of the Fhu ATPase gene, fhuC.
Expression studies on the three fhu loci demonstrated that, despite their separate acquisition, their expression was coordinately up-regulated in response to low-iron conditions. Bioinformatics on the predicted promoter regions of the fhu genes identified the binding site of the rhizobial Fur analogue, RirA, which is likely to be responsible for this expression profile.
Southern hybridisations of DNA isolated from members of the mesorhizobial population revealed the three fhu loci were not conserved in the mesorhizobial population. The presence of FhuA was the best predictive marker for the trait. It is proposed that multiple rounds of acquisitions and recombinations, both illegitimate and legitimate, formed this transporter, with the constant need for iron offset by the negative selection pressure of FhuA being a target for phage. None of the Fhu-specific genes was present in the sequenced M. loti strain MAFF303099 though flanking sequences were, further emphasizing the role of genome microevolution in forming the Fhu phenotype.
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Angeloni, Stephen V. "Characterization of the nifUHD cluster and a new myoglobin-like gene from Nostoc commune UTEX 584." Diss., Virginia Tech, 1992. http://hdl.handle.net/10919/37418.
Full textAbstract:
Sequence analysis of the entire 3.5 kb HindIII genomic DNA fragment previously isolated from Nostoc commune UTEX 584 (Defrancesco and Potts 1988), determined the exact locations of the nifU, nifH, and nifD genes and identified two potential stem loop structures, a direct repeat, and an ORF that codes for a protein with a predicted amino acid sequence similar to that of myoglobin from Paramecium caudatum.
The N. commune UTEX 584 myoglobin-like protein has a predicted length of 118 amino acids and molecular mass of 12,906 Da. A PCR copy of the gene (glbN) was cloned for overexpression of the protein. The recombinant protein was purified and used for spectral analysis and for the production of polyclonal antisera.
Treatment of the recombinant protein with dithionite and CO resulted in spectral shifts characteristic of hemoproteins that bind oxygen. While some of the spectral characteristics are unique to the protein, in general the spectra were more like those of globins than cytochromes. Based on these characteristics and the sequence similarity to the P. caudatum mnyoglobin, we proposed the name cyanoglobin, with the gene designation glbN and the protein designation GlbN.
Western analysis of GlbN expression was performed on N. commune UTEX 584 and two species of Anabaena (Anabaena sp. PCC 7120 and Anabaena variabilis). In N. commune UTEX 584 a protein with a molecular mass similar to that predicted for GlbN was detected. This protein was produced in increased amounts under the same growth conditions that resulted in increased production of nitrogenase reductase (the nifH gene product). No proteins of similar size to GlbN were detected in Anabaena sp. PCC 7120 or A. variabilis.
A possible function of GlbN may be for oxygen storage, transport, or protection of the nitrogenase system. These functions as well as those of the direct repeat and the potential stem loop structures and their relationship to nitrogen fixation or other physiological processes in N. commune UTEX 584 require further analysis.Ph. D.
19
Zhao, Lihan. "Genetic modification of nodulation and N2 fixation in soybean / Lihan Zhao." [St. Lucia, Qld.], 2004. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe18398.pdf.
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Wolfenden, J. "Nitrogen fixation associated with Spartina anglica : A study of nitrogen-fixing microorganisms and their contribution to the growth of a developing Spartina anglica marsh in the Lune Estuary." Thesis, Lancaster University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.355042.
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Harris, Kelvin. "Understanding the NifM dependence of NifH in Azotobacter vinelandii functional substitution of NifH by a NifH-ChlL chimeric construct in a NifM- strain /." Master's thesis, Mississippi State : Mississippi State University, 2007. http://library.msstate.edu/etd/show.asp?etd=etd-07062007-110702.
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Howitt, Susan M. "Nitrogen assimilation in bradyrhizobium (parasponia) SP. ANU289." Phd thesis, 1986. http://hdl.handle.net/1885/144112.
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Iismaa, Siiri Epp. "A molecular and genetic analysis of symbiotic nitrogen fixation genes in Rhizobium trifolii." Phd thesis, 1988. http://hdl.handle.net/1885/142608.
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Weinman, Jeremy John. "The molecular genetics of nitrogen fixation in the bradyrhizobium sp. (parasponia) strain ANU289." Phd thesis, 1986. http://hdl.handle.net/1885/142993.
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Fong, Allison A. "Mesoscale variability in nitrogen-fixing bacteria and rates of nitrogen fixation in the North Pacific Ocean." Thesis, 2006. http://hdl.handle.net/10125/20801.
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Rodrigues, Kevin J. "The effect of cadmium upon the growth and nitrogen fixation of the cyanobacterium Gloeothece ATCC 27152 /." 1986. https://scholarworks.umass.edu/theses/3397.
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Wiebkin, Suzanne Constance. "The enhancement of wheat growth after inoculation with free-living nitrogen-fixing bacteria." Thesis, 2003. http://hdl.handle.net/2440/115252.
Full textAbstract:
Focuses on the selection of bacteria for use as inoculants to assist in early establishment of whet in environments where winter rainfall is variable. This evokes the concept of early development of root growth. The beneficial effects on plants of mixed N₂ -fixing bacteria from 3 local soils were compared to identify soils from which to identify potential inoculants. Experiments to identify dominant bacterial species within the mixed N₂-fixing assemblage were carried out using fatty acid profiles from fatty acid methyl ester analysis (GC-FAME) and 3 were selected to be co-inoculated onto wheat. Results of inoculation indicated that raised levels of plant N in the inoculated treatments could be attributed to N2 fixation by the bacteria.Thesis (Ph.D.) -- University of Adelaide, Dept. of Soil and Water, 2003
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Hebbar, K. Prakash. "Associations between Zea Mays L. and soil bacteria." Phd thesis, 1986. http://hdl.handle.net/1885/143768.
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Ndiaye, Aissatou. "Impact of a red clover winter cover crop on carbon and nitrogen mineralization by microorganisms in soil aggregates." Thesis, 1998. http://hdl.handle.net/1957/33785.
Full textAbstract:
Although legumes have been widely studied for their nitrogen-fixing ability, it
is uncertain to what extent legume cover crops achieve their nitrogen-fixing potential
under the climatic conditions encountered in western Oregon. Furthermore, it is
unknown what factors control the proportions of legume cover crop N that are either
sequestered into soil organic matter, or that contribute to the N requirements of the
following summer crop. Soil was sampled in mid-September 1997, after harvest of a
summer broccoli crop, from plots located at the North Willamette Research and
Extension Center, Aurora, Oregon. Soil was sampled from main plots that had been
either winter cover cropped with red clover (LN��� and LN���) or fallowed during the
winter period (FN��� and FN���), and specifically from sub-plots in which the following
summer crop had received either zero (N���) or an intermediate (N���) rate of N fertilizer
as urea. Levels of total organic carbon (TOC), total Kjeldahl nitrogen (TKN), and
readily mineralizable C and N were measured in both whole soil samples and in
different aggregate-size classes (<0.25, 0.25-0.5
0.5-1.0, 1.0-2.0, and 2-5mm) prepared by dry sieving the soil. Aggregate size-class
distribution was not affected by the cover crop treatment. Although there was no significant effect of cover crop treatment on either TKN or TOC levels in whole soil samples, TOC levels were consistently higher in the small aggregate size-classes <1 mm of the fallow than the legume treatment. There was a significantly higher level of mineralizable C in the <0.25 mm size class of the legume than the fallow treatment. There was a trend for the level of mineralizable N to be greater in soil from the legume than the fallow treatment. However, N fertilizer had a significant positive effect on the level of readily mineralizable N in both fallow and legume cover-cropped treatments, it had a negative effect on TKN levels among all aggregate-size classes. There were differences in the levels of mineralizable N measured among the aggregate-size classes, and immobilization of N between 20 and 40 days of incubation also differed among the aggregate-size classes.Graduation date: 1999
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Gao, Ke. "Characterisation of the regulatory gene nolR in Sinorhizobium meliloti." Master's thesis, 2003. http://hdl.handle.net/1885/148661.
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Olsson, Jane Elizabeth. "Systemic control of soybean nodule autoregulation." Phd thesis, 1988. http://hdl.handle.net/1885/142985.
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Prayitno, Joko. "An investigation of bacterial-rice associations." Master's thesis, 2001. http://hdl.handle.net/1885/147759.
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Kifle, Medhin Hadish. "Development of free-living diazotrophic (FLD) inoculants and their effects on crop growth." Thesis, 2008. http://hdl.handle.net/10413/5277.
Full textAbstract:
In this study several free-living diazotrophs (FLD) were isolated and screened for their
nitrogen fixing ability on a range of crops grown in greenhouse, hydroponics and field trials. Rhizosphere isolates of free-living diazotrophs (FLD) may be effective biofertilizer inoculants, and may improve plant health where crops are grown with little or no fertilizer, as is the case in the Developing World. FLD isolates from rhizospheric soils in KwaZulu-Natal were assessed by growing them on N-free media, which is a key isolation method. They were then evaluated for their nitrogenase activity by quantifying ethylene production from acetylene by gas chromatography (GC). The free living isolates that produced greater quantities of ethylene were detected by an acetylene reduction assay (ARA). These were
further assessed for colony formation on N-free media with different carbon sources, and at a range of temperatures (20, 25 and 300C) and pH values (6.0, 7.0 and 8.0). Isolates G3 and L1 were identified using DNA sequencing by Inqaba Biotechnical Industries (Pty) Ltd as Burkholderia ambifaria Coenye et al, and Bacillus cereus Frankland, respectively. These isolates grew significantly better on an ethanol medium, at temperatures of 20, 25 and 300C and pHs of 6.0, 7.0 and 8.0. Isolates B3 (Burkholderia sp.) and D6 (Bacillus cereus Frankland) also grew well on an ethanol medium, but only at 200C and at a pH of 6.0 and 7.0, respectively, while Isolate E9 (Burkholderia cepacia Frankland) grew well on an ethanol medium only at 300C, and pH 6.0 and 7.0. Temperature and pH strongly influence FLD growth on N-free media using different carbon sources. Further trials were conducted to screen the best isolates under greenhouse condition, using both seed treatments and drenching application techniques onto several crops. The drenching application resulted in an increase in the growth and N-total of all the evaluated crops, relative to an unfertilized control. Growth and N-total of maize and sorghum increased with seed treatments, but did not increase the growth of lettuce and zucchini. Drenching of FLD isolates at 106cfu ml-1, applied on weekly basis, resulted in an increase in the growth of lettuce. Increased doses and frequency of application of the FLD bacteria resulted in a decrease in lettuce growth. This led to the conclusion that application of FLD bacteria at high doses and short intervals may create a situation where the applied FLD
bacteria and the resident rhizosphere microbes compete for root exudates. High doses at low frequencies and low doses at high frequencies may be more effective on lettuce.
Inoculation of Isolate L1 (B. cereus) at 106cfu ml-1 or in combination with Eco-T®
(Trichoderma harzianum Rifai), significantly increased growth of lettuce. This result may
have been due to nitrogen fixation, or to secretion of growth promoting substances by both
the FLD and T. harzianum, and to biocontrol effects of Eco-T®. Application of Isolate L1
(B. cereus) at 106cfu ml-1 with or without Eco-T® was an effective tool for enhancing plant
growth and nitrogen fixation. An FLD, Isolate L1 (B. cereus), was applied to lettuce plants together with a complete
hydroponics fertilizer at 25% strength (Ocean Agriculture 3:1:3 (38) Complete), with the N level at 25mg l-1. These plants grew significantly better than the control plants grown on 25%
of normal NPK fertilization, or with an inoculation of L1 alone. This indicates that it may be
possible to integrate FLD applications with the application of low levels of commercial
fertilizers, which is what resource poor farmers can afford.Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.