温室効果ガスを発生させる細菌はこれまで考えられていたよりも多い(Many More Bacteria Produce Greenhouse Gases than Previously Thought)

ad

2024-06-21 カリフォルニア工科大学(Caltech)

温室効果ガスを発生させる細菌はこれまで考えられていたよりも多い(Many More Bacteria Produce Greenhouse Gases than Previously Thought)
Fieldwork to understand greenhouse gases and microbial communities in Santa Barbara rangeland soils.
Credit: W. Fischer

カルテックの研究者たちは、低酸素条件下で硝酸塩を「呼吸」する新しいクラスの酵素を発見しました。この過程で温室効果ガスである亜酸化窒素(N2O)が生成されますが、亜酸化窒素は大気中で長期間残留しないため、排出を抑える対策が即座に効果を発揮します。例えば、肥料の過剰使用を減らすことで、温室効果ガス排出を削減しつつ農家のコスト削減も可能です。この研究により、亜酸化窒素の生成源が以前よりもはるかに多いことが明らかになりました。研究チームは、さまざまな環境で多くの微生物種のゲノム配列を調査し、酸素ではなく一酸化窒素を呼吸する酵素を発見しました。この研究は、硝酸塩呼吸が酸素呼吸から進化したことを示し、微生物の代謝予測の重要性を再認識させるものです。

<関連情報>

バクテリアと古細菌における一酸化窒素還元の多様性と進化 Diversity and evolution of nitric oxide reduction in bacteria and archaea

Ranjani Murali, Laura A. Pace, Robert A. Sanford, +6, and James Hemp
Proceedings of the National Academy of Sciences  Published:June 20, 2024
DOI:https://doi.org/10.1073/pnas.2316422121

Significance

With the advent of culture-independent techniques for studying environmental microbes, our knowledge of their diversity has exploded, uncovering unique organisms, pathways, and proteins carrying out important processes in the biosphere. Novel biochemical reactions are often proposed based on sequence data, but experimental validation is difficult and rare. In this work, we used environmental sequence data to find enzymes that produce the greenhouse gas N2O from NO and validated our hypothesis with experiments. These new enzymes likely contribute to global N2O fluxes and expand the breadth of nitrogen cycling. We also demonstrated that these enzymes evolved multiple times from oxygen reductases, indicating that the evolutionary histories of aerobic respiration and denitrification—and more broadly the oxygen and nitrogen cycles—are tightly connected.

Abstract

Nitrous oxide is a potent greenhouse gas whose production is catalyzed by nitric oxide reductase (NOR) members of the heme-copper oxidoreductase (HCO) enzyme superfamily. We identified several previously uncharacterized HCO families, four of which (eNOR, sNOR, gNOR, and nNOR) appear to perform NO reduction. These families have novel active-site structures and several have conserved proton channels, suggesting that they might be able to couple NO reduction to energy conservation. We isolated and biochemically characterized a member of the eNOR family from the bacterium Rhodothermus marinus and found that it performs NO reduction. These recently identified NORs exhibited broad phylogenetic and environmental distributions, greatly expanding the diversity of microbes in nature capable of NO reduction. Phylogenetic analyses further demonstrated that NORs evolved multiple times independently from oxygen reductases, supporting the view that complete denitrification evolved after aerobic respiration.

生物化学工学
ad
ad
Follow
ad
タイトルとURLをコピーしました