Methane Production by Facultative Anaerobic Wood-Rot Fungi via a New Halomethane-Dependent Pathway

The greenhouse gas methane (CH(4)) is of pivotal importance for Earth’s climate system and as a human energy source. A significant fraction of this CH(4) is produced by anaerobic Archaea. Here, we describe the first CH(4) production by facultative anaerobic wood-rot fungi during growth on hydroxylated/carboxylated aromatic compounds, including lignin and lignite. The amount of CH(4) produced by fungi is positively correlated with the amount of CH(3)Cl produced during the rapid growth period of the fungus. Biochemical, genetic, and stable isotopic tracer analyses reveal the existence of a novel halomethane-dependent fungal CH(4) production pathway during the degradation of phenol and benzoic acid monomers and polymers and utilization of cyclic sugars. Even though this halomethane-dependent pathway may only play a side role in anaerobic fungal activity, it could represent a globally significant, previously overlooked source of biogenic CH(4) in natural ecosystems. IMPORTANCE Here, we demonstrate that wood-rot fungi produce methane anaerobically without the involvement of methanogenic archaea via a new, halomethane-dependent pathway. These findings of an anaerobic fungal methane formation pathway open another avenue in methane research and will further assist with current efforts in the identification of the processes involved and their ecological implications.