Hydrazine Synthase From Anammox Is Inhibited by Linear and Aromatic Alkynes
Cerys Maryan1, Guylaine H L Nuijten2, Andrew T Crombie1
1School of Biological Sciences, University of East Anglia, Norwich, UK.
Environmental Microbiology
|February 28, 2026
Summary
Short-chain alkynes inhibit anaerobic ammonium oxidation (anammox) by targeting hydrazine synthase. Longer-chain alkynes do not affect anammox, making 1-octyne suitable for quantifying N₂O emissions from ammonia-oxidizing bacteria and archaea.
Area of Science:
- Environmental Microbiology
- Biogeochemistry
- Biochemical Toxicology
Background:
- Nitrous oxide (N₂O) emissions are often quantified using selective inhibitors like 1-alkynes.
- The impact of these inhibitors on anaerobic ammonium-oxidizing (anammox) bacteria remains poorly understood.
- Anammox bacteria play a crucial role in nitrogen cycling and mitigating N₂O production.
Purpose of the Study:
- To investigate the inhibitory effects of linear and aromatic alkynes on anammox bacteria.
- To identify the specific enzyme targeted by these alkynes within the anammox pathway.
- To determine the suitability of alkynes as selective inhibitors for differentiating N₂O sources.
Main Methods:
- Incubation of 'Candidatus Kuenenia stuttgartiensis' and wetland soil with various linear (C₂-C₈) and aromatic alkynes.
- Measurement of anammox activity using ¹⁵N-nitrite tracer and ²⁹N₂ production.
- Assessment of hydrazine oxidation activity and N₂O production in the presence of an NO donor.
Main Results:
- Short-chain linear alkynes (C₂-C₅) significantly suppressed anammox activity.
- Hydrazine oxidation activity remained unaffected, indicating inhibition upstream of hydrazine dehydrogenase.
- Cessation of ²⁹N₂ production with an NO donor implicated hydrazine synthase as the target enzyme.
- Alkynes longer than C₅ and aromatic alkynes showed no inhibitory effect on anammox.
Conclusions:
- 1-octyne is a suitable selective inhibitor for distinguishing N₂O contributions from ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA).
- Understanding alkyne inhibition mechanisms is crucial for accurate environmental N₂O emission estimations.
- This study provides a refined method for assessing microbial contributions to N₂O production in various environments.
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