A New Discovery to Save the Earth! What is the Revolutionary Protein Tackling Greenhouse Gas Reduction? ─ A New Strategy for Greenhouse Gas Elimination Starting from the Soil

Introduction: A Protein That Changes the "Premise" Has Been Found

On October 21, 2025, Phys.org reported news that added new terrain to the map of greenhouse gas countermeasures. A research team led by the University of Tennessee, Knoxville, reported an unknown protein family that reduces N₂O (nitrous oxide) to climate-neutral nitrogen (N₂). In existing textbooks, N₂O reductase (N₂OR, gene name nosZ) has been organized into two "clades." However, this newly discovered protein is significantly different from both at the sequence level, forming a "third clade." Its function was confirmed through a combination of AI-based structural predictions, mass spectrometry, and cultivation experiments.phys.org

Background: Why Is N₂O Troublesome?

N₂O has a much stronger greenhouse effect per unit mass compared to CO₂ and also destroys stratospheric ozone. Since the spread of synthetic nitrogen fertilizers, it has been well-known that nitrogen left in agricultural soils is converted by microorganisms, leading to the generation of large amounts of N₂O. The University of Tennessee's explanation succinctly illustrates its troublesome nature with the metaphor "about 300 times that of CO₂." Therefore, understanding the microorganisms and enzymes that "erase N₂O" in the soil is directly linked to practical climate measures.cee.utk.edu

What's New: L-N2OR / L-NosZ

The research team had previously demonstrated in 2024 that sustainable N₂O reduction occurs even in acidic soils. Through subsequent large-scale metagenomic and metaproteomic analyses and the latest structural predictions, they identified a group of proteins that show less than 40% similarity to known nosZ but share key motifs in their three-dimensional structure and actually reduce N₂O to N₂. This was reported as "L-N2OR (lactonase-type N₂O reductase)." Phylogenetically, it lies outside existing frameworks and is distributed across a wide range of clades, including difficult-to-culture groups like Nitrospinota.NaturePubMed

There are three key points.

1. Despite distant sequences, the structure and function are similar—this can be interpreted as an example of convergent evolution.

2. The genome reference library will be updated—previously overlooked "similar but different" sequences can now be automatically identified as N₂O reduction candidates.

3. Nitrogen cycle models need recalibration—the estimate of "where and how much N₂O is disappearing" may change.phys.org

Essence of the Experiment: AI × Mass Spectrometry × Cultivation

The paper (Nature, 2025) demonstrated the function by accelerating the N₂O reduction rate in cultivation systems, identifying protein groups specifically expressed in the presence of N₂O, and stacking structural elements corresponding to NosZ at the ribbon diagram level. Particularly, the proteomic behavior of surrounding gene groups detected only in the presence of N₂O reinforces the consistency as a metabolic pathway.phys.org

"Reinterpretation of Past Research" Begins

As pointed out by the research team, once this family is incorporated into reference databases, retrospective explanations can be provided for previously unexplained N₂O reduction activities through reanalysis of existing data. The 2024 report that demonstrated the presence of microbial communities that reduce N₂O in conjunction with growth under acidic conditions was one such starting point.Nature

Applicability: Scenarios for Field Implementation

• Soil Amendments/Biostimulants: Select and acclimate microorganisms with L-N2OR and return them to the soil to suppress the N₂O peak after fertilizer application.

• Biofilters in Livestock and Biogas Facilities: Design bioreactors adapted to high-concentration N₂O gas streams.

• Monitoring: Quantify the N₂O "sink capacity" of soil and aquatic environments using the L-N2OR gene as a biomarker.
  These do not imply immediate productization, but it is certain that the scope of exploration will expand beyond designs based solely on known NosZ clades I and II.PubMed

Risks and Constraints: Not a "Panacea"

• Intervention in Ecosystems: The introduction of non-native strains carries ecological risks such as competition and horizontal gene transfer.

• Environmental Dependency: Activity varies greatly depending on field conditions such as pH, carbon sources, and redox states. Although sustainability in acidic soils has been suggested, it is not universal.

• Measurement Challenges: Due to the spatial scale dependency of flux measurements and isotope methods, ensuring statistical power for effect verification is difficult.

• Regulation: Regardless of GMO/non-GMO status, environmental safety assessments are required for actual field trials.Nature

SNS Reactions: A Balance Between "Expectation" and "Caution"

The paper was published by 'Nature' in late August, and shortly thereafter, the official Nature X account introduced it. Starting from the spread of the post, interest in the "third N₂O reductase" surged within the climate and agricultural communities. It was also visualized on Nature's official Facebook page and science media Instagram, spreading the topic to the general public. The trends can be summarized as follows:

• Welcoming Mood: Evaluated as "There were few trump cards for N₂O compared to CO₂ measures. This is a breakthrough."

• Implementation Questions: Specific questions about technical conditions like "When and how to introduce it into the soil? Isn't it weak to oxygen? Can it be measured?"

• Skepticism and Cautious Optimism: Cool-headed remarks like "Lab activity doesn't necessarily translate to the field. Long-term data is needed."
  These are summaries based on actual posts on SNS (Nature's X/Facebook, science-related Instagram posts), characterized by a balance between enthusiasm and realism.X (formerly Twitter)Facebook

Why the "Third Clade" Is Important

Since the 2010s, the nosZ gene has been broadly classified into "typical (clade I)" and "atypical (clade II)," with the latter attracting attention as N₂O sinks because it includes bacteria that reduce only N₂O without denitrification. The L-N2OR identified in this study is groundbreaking in that it visualizes groups that are "structurally similar but distantly related in sequence," beyond those defined frameworks. The geographical distribution and contribution rate of previously overlooked N₂O sinks may be revised upward.ASM Journals

Future Verification Points

1. Reproducibility in the Field: On-site verification under dynamic conditions such as post-rainfall and post-fertilization peaks.

2. Host Range and Ecological Niche: In which taxonomic groups and environments is it most active (e.g., Nitrospinota).

3. Synthetic Biology: Can L-N2OR function be transferred to a safe host and stably expressed and activated?

4. Model Integration: Incorporate the new family into climate and nitrogen cycle models to quantify reduction potential by region.PubMed

Conclusion: "Visualization" Changes Strategies

In combating global warming, the key lies not only in CO₂ but also in the "visualization" and enhancement of the "erasing power" of N₂O. The identification of L-N2OR/L-NosZ updates the blueprint for practical measures usable in the field (amendments, bioreactors, monitoring) and simultaneously encourages the reinterpretation of past data. The research team's discovery is positioned at the intersection of scientific foundation and policy implementation. The next step is to present sustainable effects in the field and design safe and equitable deployment.phys.org