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Microbial nitrogen metabolisms and nitrogen recycling through DNRA in low-oxygen marine waters Huggins, Julia Anne

Abstract

Microorganisms regulate global nitrogen (N) availability by conducting complex series of metabolisms that transform N compounds and can produce bio-unavailable forms of N (N-loss). N-loss primarily occurs in the absence or near-absence of oxygen (O₂), and thus O₂ emerges as an important regulator of N availability. Low-O₂ pelagic marine environments are among the largest venues for N-loss and they are currently expanding as a result of ocean deoxygenation, driven by climate change. These changes have potential to alter N availability in the ocean and create feedbacks on climate, but the outcomes are difficult to predict, partly because microbial N metabolisms are complex. Three different N metabolisms can occur under low-O₂ conditions: two metabolisms (denitrification, anammox) result in N loss, but another (DNRA) recycles N in the environment. We know relatively less about DNRA and the ways O₂ can influence N loss and recycling. In this thesis I conduct experiments in a model low-O₂ marine environment to create new knowledge about N-recycling and the ways microbial N metabolisms respond to changing O₂. In chapter 2, I test for metabolisms that can consume N₂O across a range of O₂ conditions to determine whether N₂O is lost through denitrification or recycled. I find that N₂O cannot be recycled, but N₂O-loss can still be active in the presence of low O₂. In chapter 3, I test the importance of DNRA in marine waters and generate new information about microorganisms that conduct DNRA. I find that DNRA is highly variable and can be the dominant metabolism, overall. I also find that DNRA is conducted by facultatively aerobic organisms and is most active in intermittently-oxygenated environments. In the fourth chapter I test whether low O₂ can directly regulate N loss and recycling. I find that O₂ can regulate all three metabolisms and potentially stimulate denitrification and DNRA. The observations that DNRA can be the dominant metabolism in pelagic marine environments and that O₂ can stimulate N metabolisms are two novel findings that, if widely applicable, could alter models and forecasts for deoxygenation. I suggest future work to test extensibility and build on these results.

Item Metadata

Title
Microbial nitrogen metabolisms and nitrogen recycling through DNRA in low-oxygen marine waters
Creator
Huggins, Julia Anne
Supervisor
Crowe, Sean A.
Publisher
University of British Columbia
Date Issued
2023
Description
Microorganisms regulate global nitrogen (N) availability by conducting complex series of metabolisms that transform N compounds and can produce bio-unavailable forms of N (N-loss). N-loss primarily occurs in the absence or near-absence of oxygen (O₂), and thus O₂ emerges as an important regulator of N availability. Low-O₂ pelagic marine environments are among the largest venues for N-loss and they are currently expanding as a result of ocean deoxygenation, driven by climate change. These changes have potential to alter N availability in the ocean and create feedbacks on climate, but the outcomes are difficult to predict, partly because microbial N metabolisms are complex. Three different N metabolisms can occur under low-O₂ conditions: two metabolisms (denitrification, anammox) result in N loss, but another (DNRA) recycles N in the environment. We know relatively less about DNRA and the ways O₂ can influence N loss and recycling. In this thesis I conduct experiments in a model low-O₂ marine environment to create new knowledge about N-recycling and the ways microbial N metabolisms respond to changing O₂. In chapter 2, I test for metabolisms that can consume N₂O across a range of O₂ conditions to determine whether N₂O is lost through denitrification or recycled. I find that N₂O cannot be recycled, but N₂O-loss can still be active in the presence of low O₂. In chapter 3, I test the importance of DNRA in marine waters and generate new information about microorganisms that conduct DNRA. I find that DNRA is highly variable and can be the dominant metabolism, overall. I also find that DNRA is conducted by facultatively aerobic organisms and is most active in intermittently-oxygenated environments. In the fourth chapter I test whether low O₂ can directly regulate N loss and recycling. I find that O₂ can regulate all three metabolisms and potentially stimulate denitrification and DNRA. The observations that DNRA can be the dominant metabolism in pelagic marine environments and that O₂ can stimulate N metabolisms are two novel findings that, if widely applicable, could alter models and forecasts for deoxygenation. I suggest future work to test extensibility and build on these results.
Genre
Thesis/Dissertation
Type
Text
Language
eng
Date Available
2023-10-23
Provider
Vancouver : University of British Columbia Library
Rights
Attribution-NonCommercial-NoDerivatives 4.0 International
DOI
10.14288/1.0437291
URI
http://hdl.handle.net/2429/86294
Degree
Doctor of Philosophy - PhD
Program
Microbiology and Immunology
Affiliation
Science, Faculty of; Microbiology and Immunology, Department of
Degree Grantor
University of British Columbia
Graduation Date
2023-11
Campus
UBCV
Scholarly Level
Graduate
Rights URI
http://creativecommons.org/licenses/by-nc-nd/4.0/
Aggregated Source Repository
DSpace

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Attribution-NonCommercial-NoDerivatives 4.0 International