2025-08-14 カリフォルニア大学バークレー校（UCB）
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An electron microscope image of single-celled methanogens, members of the archaea domain. They are ubiquitous in oxygen-free environments, turning simple foods into methane, a potent greenhouse gas.
Alienor Baskevitch/UC Berkeley
＜関連情報＞
- https://news.berkeley.edu/2025/08/14/scientists-hack-microbes-to-identify-environmental-sources-of-methane/
- https://www.science.org/doi/10.1126/science.adu2098
メチル-コエンザイムM還元酵素の発現調節は、微生物由来のメタン同位体組成を変える Modulation of methyl–coenzyme M reductase expression alters the isotopic composition of microbial methane
Jonathan Gropp, Markus Bill, Max K. Lloyd, Rebekah A. Stein, […] , and Daniel A. Stolper
Science Published:14 Aug 2025
DOI:https://doi.org/10.1126/science.adu2098
Editor’s summary
The isotopic composition of methane is an important signal indicating whether the molecules were produced by biological or geological processes. However, there are many factors in natural environments that are not reflected in laboratory culture conditions, and caution is necessary when making assumptions about the isotope signatures of biological methanogenesis. Gropp et al. used a CRISPR-edited model methanogen with an inducible version of methyl-CoM reductase, the key enzyme of methanogenesis. Lowered expression of this enzyme resulted in a pathway blockage that increased reversibility in the oxidative branch of methanol and acetate metabolism, resulting in an overall shift of isotopic composition in intermediates leading to methane. —Michael A Funk
Abstract
The stable isotopic composition of microbial methane varies substantially, and the underlying causes are debated. In this work, we experimentally controlled the abundance of the central enzyme in methanogenesis, methyl–coenzyme M reductase (MCR), in Methanosarcina acetivorans and tested whether its cellular concentration alters methane isotopic compositions. We found that during growth on methanol and acetate, lowering the expression of mcr increases the degree of hydrogen isotope exchange between methane and water. Using an isotope-enabled model of methanogenesis, we found that these changes result from an increase in reversibility of enzymes involved in the oxidation of the substrate methyl group. This result indicates that methane produced from organic compounds can deviate from commonly assumed pathway-specific isotope effects, with implications for the interpretation of environmentally relevant methane sources.
