It's not limited to Archaea – on methane emissions in the world of fungi

Methane (CH4) is a potent greenhouse gas, second only to carbon dioxide in driving climate change during the industrial era. CH4 warming potential is 28 times more powerful than CO2 in a 100-year timescale. Moreover, methane contributes to the formation of ground-level ozone, a dangerous air pollutant. The atmospheric amount of methane has more than doubled since pre-industrial times. To control and minimise the threat connected to methane emissions, we need to understand global CH4 sources and the processes behind them. Biogenic methane sources typically refer to archaeal methanogenesis, an anaerobic process playing a quantitatively important role in global methane emissions. However, the methane paradox is observed – although methanogenesis is expected to happen only under strictly anoxic conditions, peaks in CH4 concentrations in oxygen-saturated waters are present. Increasing evidence has confirmed that cyanobacteria, algae, and fungi could produce methane in oxic environments. Fungi not only enhance archaeal methanogenesis by initiating the degradation of organic matter, but they can also produce methane themselves. It has been shown that methane could be produced continuously under oxic conditions without any archaeal presence, i.e., by Pleurotus sapidus and Laetiporus sulphureus. It is possible to happen when various metabolites (such as methionine) are degraded, possibly as a stress response. The biochemical and physiological aspects of these processes, as well as the fungal role in the global methane cycle, remain mostly unclear. However, non-methanogenesis processes could be important contributors to global methane emissions. Here, we present current state-of-the-art concerning methane emissions in the world of fungi