New research has found that all organisms release methane. The formation of this potent greenhouse gas is triggered by reactive oxygen species and is enhanced by additional oxidative stress.
It is well known that methane, a greenhouse gas, is produced by special microorganisms, for example in the intestines of cows or in rice fields.
For some years, scientists have also observed the production of methane in plants and fungi, without finding an explanation.
Now researchers from the University of Heidelberg and the Max Planck Institute for Terrestrial Microbiology in Marburg have shed light on the underlying mechanism. Their findings suggest that all organisms release methane.
Methane is a powerful greenhouse gas, so the study of its natural and anthropogenic biogeochemical sources and sinks is of great interest.
Question of an enzyme
For many years, scientists believed that methane was only produced by single-celled microbes called Archaea, following the decomposition of organic matter in the absence of oxygen (anaerobic).
Now a collaboration of life and Earth scientists, led by Frank Keppler and Ilka Bischofs, has shown that an enzyme is not potentially necessary for methane formation, as the process can also take place via a purely molecular mechanism. chemical.
The formation of methane triggered by reactive oxygen species likely occurs in all organisms, the scientists have concluded.
To reach this conclusion, they verified reactive oxygen species-driven methane formation in more than 30 model organisms, ranging from bacteria and archaea, to yeast, plant cells, and human cell lines.
clearing up the past
The results obtained in this research, published in the journal Nature, clarify some doubts that arose 16 years ago, when the same Max Planck researchers discovered the release of methane from plants in the presence of oxygen (aerobic).
That discovery raised doubts, since the formation of methane could not be explained with the then existing knowledge about plants.
When the researchers observed that also fungi, algae and cyanobacteria (formerly blue-green algae) formed methane under aerobic conditions, enzyme activities were assumed to be responsible.
However, the researchers never found a corresponding enzyme in any of these organisms. The new study not only provides a better understanding of aerobic methane formation in the environment, but also explains previous observations about methane release from plants.
High cell activity leads to more methane
Using the bacterium Bacillus subtilis as a model, the researchers have now been able to show that there is a close connection between metabolic activity and the degree of methane formation. The process is the following.
Metabolic activity, especially under the influence of oxygen, leads to the formation of reactive oxygen species in cells, including hydrogen peroxide and hydroxyl radical.
In interaction with the essential element iron, the Fenton reaction then takes place, a reaction between reduced iron and hydrogen peroxide, leading to the formation of highly reactive tetravalent iron compounds and hydroxyl radicals.
These latter molecules drive the cleavage of a methyl radical from methylated sulfur and nitrogen compounds, for example, the amino acid methionine. In a subsequent reaction of the methyl radical with a hydrogen atom, methane is finally formed.
All reactions can take place under physiological conditions in a test tube and are significantly enhanced by biomolecules such as ATP and NADH, which are generated by cellular metabolism, the researchers explain.
Oxidative stress increases methane formation
They add that additional oxidative stress, triggered by physical and chemical factors, for example higher ambient temperatures or the addition of reactive oxygen species-forming substances, leads to an increase in methane formation in the organisms examined.
They also point out that the addition of antioxidants and the scavenging of free radicals reduces methane formation, an interaction that probably controls methane formation in organisms, as they have found in their experiments.
Thus, the study also helps explain why methane production by a given organism can vary by several orders of magnitude, and why stressors particularly affect the amount of production.
Changes in temperature and environmental conditions caused by ​​by climate change could potentially influence the stress levels of many organisms and thus their atmospheric methane emissions.
Conversely, variations in breath methane content could indicate age- or stress-related changes in cellular metabolism, the researchers conclude.
Reference
Methane formation driven by reactive oxygen species across all living organisms. Leonard Ernst et al. Nature (2022). DOI:https://doi.org/10.1038/s41586-022-04511-9