Thesis (Ph.D.)--University of Alberta, 2010. / Title from PDF file main screen (viewed on July 13, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Soil Science, Department of Renewable Resources, University of Alberta. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography (leaves 84-91).

Presented as Thesis (Ph. D.)--University of Wisconsin--Madison, 1917. / Cover title. Reprinted from Journal of agricultural research, vol. XII, no. 8 (25 Feb. 1918). Includes bibliographical references (p. 500-504).

Thesis (Ph. D.)--Oregon State University. / Third progress report for grant NSF G-21015 initiated January 1, 1962. Contribution to project on Influence of interplanted and pure stands of red alder (Alnus rubra) on microbial activity and carbon-nitrogen transformations in soils of the Douglas-fir region. Progress report for NSF grant: G21015. Includes bibliographical references (leaves 152-164). Also available online.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2006 / Includes bibliographical references.

Magister Scientiae - MSc / The major objective of this study was to investigate soil ammonia-oxidizing bacterial diversity and composition associated with plant roots of Proteaceae plants and to compare it with non-plant associated soil. / South Africa

Philosophiae Doctor - PhD / Soil communities are regarded as among the most complex and diverse assemblages of microorganisms with estimated bacterial numbers in the order of 109-1 cells.g. Studies on extreme soils however, have reported lower cell densities, supporting the perception that the so-called extreme environments exhibit low species diversity. To assess the extent of microbial diversity within an extreme environment, the mineral soils of the Dry Valleys, Ross Dependency, Eastern Antarctica were investigated using 16S rDNA analysis. Three mineral soils designated MVG, PENP and BIS were analysed, each differing with respect to altitude, protein, lipid, water and DNA content. The mid-altitude sample, MVG, yielded the highest levels of DNA and the low altitude BIS soil contained the highest levels of protein, lipid and water. 16S clone libraries were constructed and 60 unique clones were identified and sequenced. BLASTn analysis revealed eight phylogenetic groups with Cyanobacteria, Actinobacteria and Acidobacteria representing the majority. The Cyanobacterial phylotypes were unique to the desiccated high-altitude soils of the PENP sample, suggesting a soil-borne Cyanobacterial population. 21% of the phylotypes identified were assigned as ‘uncultured’. DNA isolated from the Antarctic mineral soils was also used to construct a metagenomic clone library consisting of 90700 clones with an average insert size of 3.5 kb, representing an estimated 3.4% of the available metagenome. Activity-based screening of the library for genes conferring lipolytic activity yielded no positive clones. It is suggested that the failure to produce positive clones might be a result of insufficient nucleotide coverage of the metagenomic DNA. The metagenomic DNA extracted from the Dry Valley mineral soils was further analyzed using PCR. Two sets of degenerate primers based on conserved regions within lipolytic genes were used to target lipase and esterase genes. One set of primers was selected from a previous study. A second primer set was designed manually from amino acid alignments of true lipase genes from family I, sub-families I-VI. PCR analysis resulted in nine partial gene fragments varying between 240 bp and 300 bp. Bioinformatic analysis revealed that all nine partial gene fragments harboured α/β-hydrolase motifs, putatively identifying two esterases and three lipases from both bacterial and fungal origin. / South Africa

Magister Scientiae - MSc / 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. / South Africa

The relationship between plants and rhizosphere bacteria collected from a 45 year old permanent pasture was investigated. Several methods of strain identification within Rhizobium trifolii were evaluated. Separation of bacterial isolates based on differences in intrinsic antibiotic resistance was not appropriate because strains developed hybrid resistance patterns when grown in a common broth. Serological analyses of bacterial antigens using polyclonal antiserum yielded two reliable methods for identifying R. trifolii isolates. Agglutination and immunofluorescence procedures were not useful in distinguishing these strains but immunodiffusion and the enzyme-linked immunosorbent assay (ELISA) were highly suitable. Adaptation of the ELISA allowed isolates to be identified directly from individual root nodules without first subculturing the bacteria. A strain of Bacillus polymyxa isolated from the same pasture was shown to stimulate growth of crested wheatgrass (Agropyron cristatum L.) and white clover (Trifolium repens L.). The primary manifestation of the effect was increased root weight (P < 0.05), but shoot responses were also observed. Perennial ryegrass (Lolium perenne L.) generally reacted negatively to inoculation with this bacterium. Further stimulation of growth was noted when ramets of the white clover genotype homologous to (sharing a common origin) B. polymyxa were inoculated in pure stands (P < 0.05). Clones of the homologous perennial ryegrass genotype also showed a yield increase from slightly below control levels to slightly above them when tested in a similar manner. Detailed analysis of the crested wheatgrass response to inoculation revealed that bacterial production of indole acetic acid was the most likely cause of the growth stimulation. Other bacterial characteristics such as the ability to fix atmospheric nitrogen or to solubilize organic phosphorus were concluded to be unrelated to the growth response. Co-adaptive compatibility between genotypes of L. perenne and T. repens was not apparent when the effect of R. trifolii was ignored. However, when clones of pasture plants that had been neighbours in the field were inoculated with R. trifolii isolated from root nodules of the "parental" clover genotype, biotic specialization between the pasture plants became evident. The magnitude of the effect, which was characterized by superior white clover yields (P < 0.05), could be largely accounted for by the presence of the adapted L. perenne/R. trifolii combinations, regardless of the white clover genotype. Since T. repens was the dominant component in the species mixture, these trends were also apparent when total forage biomass was analyzed (P < 0.05). However, ecological combining ability was found to be lowest in these associations (P < 0.05). Similar experimentation with isolates of B. polymyxa (or B. polymyxa-like organisms) was performed. Again the grass/bacteria combination was shown to be influential in the growth response as the presence of homologous L. perenne/B. polymyxa combinations resulted in superior white clover and perennial ryegrass performance (P < 0.05). When T. repens was inoculated with a mixture of R. trifolii strains, unrelated isolates formed more root nodules than did homologous ones (P < 0.05). The presence of perennial ryegrass did not mitigate this effect. However, when homologous R. trifolii was administered as a single strain inoculum, yield advantages in white clover were observed (P < 0.05). If B. pol ymyxa was present, homologous strains of R. trifolii tended to form most of the root nodules regardless of the T. repens or L. perenne genotypes. The significance of the yield advantages observed in various two and three-way plant/microbe genotype combinations is discussed with respect to above ground plant performance. / Land and Food Systems, Faculty of / Graduate

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