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Measurement of the Potential Rates of Dissimilatory Nitrate Reduction to Ammonium Based on 14NH4+/15NH4+ Analyses via Sequential Conversion to N2O
Published on: October 7, 2020
Respiratory nitrate ammonification by Shewanella oneidensis MR-1
Claribel Cruz-García1, Alison E Murray, Joel A Klappenbach
1Center for Microbial Ecology, Michigan State University, East Lansing, MI 48824-1325, USA.
Journal of Bacteriology
|November 14, 2006
Summary
Shewanella oneidensis MR-1 reduces nitrate to ammonium, a process called respiratory nitrate ammonification. This bacterium does not perform respiratory denitrification, as confirmed by gene deletion studies.
Area of Science:
- Microbial Metabolism
- Anaerobic Respiration
- Biogeochemical Cycling
Background:
- Shewanella oneidensis MR-1 is a model organism for studying anaerobic respiration.
- Nitrate reduction is a key process in microbial biogeochemical cycles, with various end products.
- Understanding the specific pathways utilized by S. oneidensis MR-1 is crucial for predicting its environmental role.
Purpose of the Study:
- To investigate the anaerobic respiratory pathways of Shewanella oneidensis MR-1 using nitrate as the electron acceptor.
- To determine if S. oneidensis MR-1 performs respiratory denitrification or nitrate ammonification.
- To confirm the role of the periplasmic nitrate reductase (NapA) in nitrate metabolism.
Main Methods:
- Anaerobic cultivation of Shewanella oneidensis MR-1 with nitrate as the sole electron acceptor.
- Analysis of end products including ammonium, dinitrogen, and nitrous oxide.
- Construction and characterization of a mutant lacking the napA gene.
Main Results:
- Sequential reduction of nitrate to nitrite and then to ammonium was observed.
- Minimal production of dinitrogen and nitrous oxide, with no growth on nitrous oxide.
- A napA deletion mutant showed no nitrate respiration or assimilation, confirming NapA as the sole nitrate reductase.
Conclusions:
- Shewanella oneidensis MR-1 exclusively performs respiratory nitrate ammonification (dissimilatory nitrate reduction to ammonium).
- The bacterium does not engage in respiratory denitrification under these conditions.
- The NapA enzyme is essential and solely responsible for nitrate reduction in S. oneidensis MR-1.
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