Methane formation in aerobic environments

Abstract

Environmental context. Methane is an important greenhouse gas and its atmospheric concentration has drastically increased since pre-industrial times. Until recently biological methane formation has been associated exclusively with anoxic environments and microbial activity. In this article we discuss several alternative formation pathways of methane in aerobic environments and suggest that non-microbial methane formation may be ubiquitous in terrestrial and marine ecosystems. Abstract. Methane (CH4), the second principal anthropogenic greenhouse gas after CO2, is the most abundant reduced organic compound in the atmosphere and plays a central role in atmospheric chemistry. Therefore a comprehensive understanding of its sources and sinks and the parameters that control emissions is prerequisite to simulate past, present and future atmospheric conditions. Until recently biological CH4 formation has been associated exclusively with anoxic environments and methanogenic activity. However, there is growing and convincing evidence of alternative pathways in the aerobic biosphere including terrestrial plants, soils, marine algae and animals. Identifying and describing these sources is essential to complete our understanding of the biogeochemical cycles that control CH4 in the atmospheric environment and its influence as a greenhouse gas.

Evidence for methane production by saprotrophic fungi

“…This is in accordance with the findings of Ghyczy et al 9,12 who demonstrated that endothelial cells from rat liver produced CH 4 when exposed to site-specific inhibitors of the ETC. It would seem that aerobic CH 4 formation is not only a result of chemical formation from dead biomass as previously shown by several studies 8,11 but might also have a physiological role in eukaryotic groups such as fungi, animals and plants. For example aerobic CH 4 formation may be an integral part of cellular responses towards changes in oxidative status present in all eukaryotes.…”

“…Thus, much more knowledge on effects of species and environmental controls are needed to estimate their true impact on the cycling of global CH 4 . Moreover, in nature it might be extremely difficult to distinguish between different CH 4 formation (and also consumption) processes as recently experienced with the formation of CH 4 from vegetation 8,11 . For example, Mukhin and Voronin 27 reported a wood decay-associated CH 4 formation caused by fungi in boreal forests.…”

“…The finding that dead and living plants can emit CH 4 under oxic conditions and without the intervention of microorganisms 7,8,10 justifies a search for other biotic but non-prokaryotic CH 4 sources in fungi and animals 11 . Less well known are the findings of Ghyczy et al 9,12 who demonstrated that endothelial cells from rat liver produced CH 4 when exposed to site-specific inhibitors of the electron transport chain (ETC).…”

Metaproteogenomic analysis of microbial communities in the phyllosphere and rhizosphere of rice

“…Since the discovery of methane production by plant leaves and a few reports about the isolation of methanotrophs from plant material, it has been speculated that methanotrophs, and thus methaneoxidizing activity, might be of relevance in the plant phyllosphere (Keppler et al, 2009). However, no study in which the microbial community composition in the phyllosphere has been analyzed based on cultivation-independent methods has reported the presence of known methanotrophs.…”

A novel pathway of direct methane production and emission by eukaryotes including plants, animals and fungi: An overview

“…Whether the observed CH 4 is from plants or other sources (e.g. soil or plant water) and whether plants have their own mechanism(s) to produce CH 4 have been debated (Bruhn et al, 2012;Keppler et al, 2009;Nisbet et al, 2009). Evidence is now accumulating to indicate that plants can produce CH 4 even in the presence of oxygen (Bruggemann et al, 2009;Bruhn et al, 2009Bruhn et al, , 2014Cao et al, 2008;Fraser et al, 2015;Keppler et al, 2008;Lenhart et al, 2014;McLeod et al, 2008;Messenger et al, 2009;Mikkelsen et al, 2011;Reid, 2009, 2011;Sanhueza and Donoso, 2006;Sinha et al, 2007;Vigano et al, 2009Vigano et al, , 2008Wang et al, 2009aWang et al, , 2009bWang et al, , 2011aWatanabe et al, 2012;Wishkerman et al, 2011).…”