Genomic and Physiological Analysis of Nitrogen Oxide Metabolism in Ammonia-Oxidizers

• Author / Creator

  Kozlowski, Jessica A.

• Ammonia oxidizers come from two different domains of life, the Archaea and Bacteria, and control a vital step in the global biogeochemical Nitrogen cycle; the conversion of ammonia to nitrite. They are abundant in a wide range of environments including marine and freshwaters, terrestrial soils, and wastewater treatment plants. This group of organisms has also been implicated in the production of the nitrous oxide, a potent greenhouse gas. Nitrous oxide has been measured from ammonia oxidizing bacteria and archaea in pure and enrichment culture but the pathways, including enzymology, intermediates, and physiological conditions for nitrous oxide production are not well understood and therefore it is not possible to accurately model contributions of this group of microorganisms to global nitrous oxide emissions. The issue has been exacerbated by lack of available and closed genomes of ammonia oxidizers, physiological analyses of nitrous oxide production on pure cultures under environmentally relevant conditions, and chemical controls to elucidate differences in biological versus abiotic contributions to nitrous oxide production. Necessary studies to fill in the gaps in knowledge hindering the field were done by utilizing various approaches to studying ammonia oxidizer physiology. Physiological experiments included growth and resting cell assays along with headspace gas measurements, and instantaneous measurements of nitric oxide and nitrous oxide production during oxidation of native energy generating substrates. All studies were complemented with a genome-inferred approach to see if genomic inventory could explain physiological results. In conclusion, the present body of work addresses the above overarching problems in the field of Nitrification by (1) determining the pathways, including enzymology, involved in nitrous oxide production by the model ammonia-oxidizing bacterium Nitrosomonas europaea ATCC 19718, (2) showing that genomic inventory and phylogeny of ammonia oxidizing bacteria do not predict contributions to nitrous oxide production, and (3) identifying key pathways and intermediates that explain differences in ammonia oxidation and nitrous oxide production between ammonia oxidizing bacteria and archaea.

• Subjects / Keywords

  • Nitrous oxide
  • Nitrifier denitrification
  • Ammonia-oxidizers

• Graduation date

  Fall 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3862BR5K

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.