EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Methane formation across living organisms driven by ROS: new perspectives for understanding of biochemical methane formation and cycling on Earth

Frank Keppler1,2, Leonard Ernst1,3,4, and Ilka Bischofs3,4,5
Frank Keppler et al.
  • 1University of Heidelberg, Institute of Earth Sciences, Heidelberg, Germany (
  • 2Heidelberg Center for the Environment (HCE), Heidelberg University, 69120 Heidelberg, Germany
  • 3BioQuant Center, Heidelberg University, Im Neuenheimer Feld 267, 69120 Heidelberg, Germany
  • 4Max-Planck-Institute for Terrestrial Microbiology, Karl-von-Frisch Straße 10, 35043, Marburg, Germany
  • 5Zentrum für Molekulare Biologie Heidelberg (ZMBH), Heidelberg University, Im Neuenheimer Feld 282, 69120, Heidelberg, Germany

Methane (CH4) is the most abundant hydrocarbon in the atmosphere, largely originating from biogenic sources that recently have been linked to an increasing number of organisms living in both oxic and anoxic environments. Traditionally, biogenic CH4 has been regarded as the final product of the anoxic decomposition of organic matter by methanogenic Archaea. However, plants, fungi, algae, lichens and cyanobacteria have recently been shown to produce CH4 in the presence of oxygen. While methanogens produce CH4 enzymatically during anaerobic energy metabolism, the requirements and pathways for CH4 production by “non-methanogenic” cells are poorly understood. Here, we present a CH4 formation mechanism that most likely occurs in all living organisms (Ernst et al. 2022). Firstly, we show results from two bacterial species (Bacillus subtilis and Escherichia coli) demonstrating that CH4 formation is triggered by free iron and reactive oxygen species (ROS), which are generated by metabolic activity and enhanced by oxidative stress. ROS-induced methyl radicals, derived from organic compounds containing sulfur- or nitrogen-bonded methyl groups, are key intermediates that ultimately lead to CH4.

In a second step, we made numerous experiments and collected data from many other model organisms (over 30 species) from the three domains of life (Bacteria, Archaea and Eukarya), including several human cell lines and a non-methanogenic archaeal species. All of the selected species clearly showed CH4 formation under sterile growth conditions. As the mechanism described for CH4 formation depends on several factors such as the availability of methylated precursor compounds, free iron, cellular stress factors and antioxidants, production rates can vary by several orders of magnitude. For terrestrial plants and cyanobateria, measured CH4 emission rates have been reported to vary by almost four orders of magnitude. In both cases, rates were measured for many species and under varying environmental conditions and stressors, although the formation mechanism(s) were unknown. Our proposed ROS-driven pathway not only provides a mechanistic explanation for the observed CH4 emissions under oxic conditions but also for the large variability of emission rates observed for terrestrial plants, marine and freshwater algae, fungi, lichens and cyanobacteria, which have caused many controversial discussions since their publication. Furthermore, now it is very clear that any global upscaling will be highly challenging given the complex variables that control emissions from specific organisms.

In summary, the observed and experimental validated process of CH4 formation across all living organisms is a major step to better understand biological CH4 (in addition to the well-described archaeal methanogenesis) formation and cycling on Earth.


Ernst, L., Steinfeld, B., Barayeu, U., Klintzsch, T., Kurth, M., Grimm, D., Dick, T.P., Rebelein, J.G., Bischofs, I.B., Keppler, F. (2022). ROS-driven methane formation across living organisms. Nature, in press.

How to cite: Keppler, F., Ernst, L., and Bischofs, I.: Methane formation across living organisms driven by ROS: new perspectives for understanding of biochemical methane formation and cycling on Earth, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10255,, 2022.