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Nitrous oxide (N2O) is a potent greenhouse gas and a major cause of ozone depletion. One-third of atmospheric N2O originates in aquatic environments. Reduction of N2O to dinitrogen gas (N2) requires the nitrous oxide reductase enzyme, which is encoded by the genenosZ. Organisms that containnosZare the only known biological sinks of N2O and are found in diverse genera and a wide range of environments. The two clades ofnosZ(Clade I and II) contain great diversity, making it challenging to study the population structure and distribution ofnosZcontaining organisms in the environment. A database of over 11,000nosZsequences was compiled from NCBI (representing diverse aquatic environments) and unpublished sequences and metagenomes (primarily from oxygen minimum zones, OMZs, where N2O levels are often elevated). Sequences were clustered into archetypes based on DNA and amino acid sequence identity and their clade, phylogeny, and environmental source were determined. Further analysis of the source and environmental distribution of the sequences showed strong habitat separation between clades and phylogeny. Although there are more Clade InosZgenes in the compilation, Clade II is more diverse phylogenetically and has a wider distribution across environmental sources. On the other hand, Clade InosZgenes are predominately found within marine sediment and are primarily from the phylum Pseudonomonadota. The majority of the sequences analyzed from marine OMZs represented distinct phylotypes between different OMZs showing that thenosZgene displays regional and environmental separation. This study expands the known diversity ofnosZgenes and provides a clearer picture of how the clades and phylogeny ofnosZorganisms are distributed across diverse environments.
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Non‐denitrifier nitrous oxide reductases dominate marine biomes
Summary Microbial enzymes often occur as distinct variants that share the same substrate but differ in substrate affinity, sensitivity to environmental conditions, or phylogenetic ancestry. Determining where variants occur in the environment helps identify thresholds that constrain microbial cycling of key chemicals, including the greenhouse gas nitrous oxide (N2O). To understand the enzymatic basis of N2O cycling in the ocean, we mined metagenomes to characterize genes encoding bacterial nitrous oxide reductase (NosZ) catalyzing N2O reduction to N2. We examined data sets from diverse biomes but focused primarily on those from oxygen minimum zones where N2O levels are often elevated. With few exceptions, marinenosZdata sets were dominated by ‘atypical’ clade II gene variants. AtypicalnosZhas been associated with low oxygen, enhanced N2O affinity, and organisms lacking enzymes for complete denitrification, i.e., non‐denitrifiers. AtypicalnosZ often occurred in metagenome‐assembled genomes (MAGs) with nitrate or nitrite respiration genes, although MAGs with genes for complete denitrification were rare. We identified atypicalnosZ in several taxa not previously associated with N2O consumption, in addition to known N2O‐associated groups. The data suggest that marine environments generally select for high N2O‐scavenging ability across diverse taxa and have implications for how N2O concentration may affect N2O removal rates.
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- Award ID(s):
- 1831582
- PAR ID:
- 10455402
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Environmental Microbiology Reports
- Volume:
- 12
- Issue:
- 6
- ISSN:
- 1758-2229
- Format(s):
- Medium: X Size: p. 681-692
- Size(s):
- p. 681-692
- Sponsoring Org:
- National Science Foundation
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