Non-enzymatic methane formation by aerobic organisms

Abstract Methane (CH4) is the most abundant organic compound in the atmosphere, largely originating from anthropogenic and natural biogenic sources1. Traditionally, biogenic CH4 has been regarded as the final product of the anoxic decomposition of organic matter by methanogenic Archaea. However, plants2–4, fungi5, algae6,7 and cyanobacteria8 have recently been shown to produce CH4 in the presence of oxygen. While methanogens produce CH4 enzymatically during anaerobic energy metabolism9, the requirements and pathways for CH4 production by “non-methanogenic” cells are poorly understood. Here we demonstrate that CH4 formation by Bacillus subtilis is triggered by free iron species, enhanced by oxidative stress and restricted to metabolically active life-cycle stages. We also show that other model organisms from Bacteria and Eukarya including a human cell line release CH4 and respond to inducers of oxidative stress by enhanced CH4 formation. Our results imply that all living cells possess a common mechanism of CH4 formation without the need for specific enzymes. We propose that CH4 formation is a conserved feature of living systems which is coupled to metabolic activity and the concomitant generation of reactive oxygen species. Our findings open new perspectives for our understanding of environmental CH4 cycling, oxidative stress responses and the search for extraterrestrial life.