Exploring nitrifier denitrification in Nitrosomonas communis and Nitrosomonas europaea through physiology and proteomic analysis

• Author / Creator

  Gomes-Yakiwchuk, Sujani

• The current understanding of how ammonia oxidizing bacteria (AOB) produce the potent greenhouse gas nitrous oxide is incomplete and inaccurate since most studies are focused on the model organism for the group, Nitrosomonas europaea, which does not represent the physiological diversity of AOB. Since AOB are recognized as significant contributors to global nitrous oxide emissions, it is imperative that we study more species of AOB to refine our mechanistic understanding of how they produce nitrous oxide at the molecular level. efining this knowledge is necessary for making informed decisions about increasing the sustainability of the processes on which AOB have a major impact, such as agriculture and wastewater treatment. The overall goal of this study was to uncover the enzymes involved in the production of nitrous oxide in the ammonia oxidizing bacterium, Nitrosomonas communis, which retains the ability to produce nitrous oxide despite lacking the canonical nitrite reductase (NirK) that was thought to be essential for this process. To confirm the ability of N. communis to produce nitrous oxide, the growth of the strain was observed in batch cultures where oxygen and the growth substrate, ammonium, were limited. Nitrite and nitrous oxide production were correlated with the consumption of ammonia and oxygen with nitrous oxide production starting at the onset of hypoxia. To ensure that the observed nitrous oxide production was from enzymatic nitrite reduction, resting cell assays were conducted where stationary phase cells were
  removed from growth medium and incubated in small vials with an external reductant (PMS + Ascorbic acid, or hydrazine) under anoxia. Nitrous oxide was observed only in vials containing live cells. While the nitrous oxide-producing ability of N. communis was confirmed, it was also observed that the amounts of N2O produced were much less than the amounts
  produced by N. europaea under the same conditions, suggesting that the enzymology for nitrous oxide production was different between the two species. This was confirmed by examining the proteome of N. communis and N. europaea at mid-log phase and stationary phase. The canonical nitrite reductase, NirK, and nitric oxide reductase, NorB, were not present in the N. communis proteome in contrast to that of N. europaea. Candidates for an alternate nitrite reductase were identified in the N. communis proteome along with several cytochromes that are speculated to contribute to nitrous oxide production. While further research is necessary to confirm the role of these candidate enzymes in nitrous oxide production, this study highlights the metabolic diversity of AOB and the need to study more of them to further understand the microbial processes that contribute to greenhouse gas production.

• Subjects / Keywords

  • Nitrification
  • Nitrifier denitrification
  • Ammonia oxidizing bacteria
  • Nitrogen cycle
  • Nitrous oxide
  • Greenhouse gas production

• Graduation date

  Spring 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-6c65-bs47

• 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.