Harnessing fungi to mitigate CH₄ in natural and engineered systems

Methane (CH₄) is a powerful greenhouse gas emitted from natural and anthropogenic sources, and its emission rates vary among sources as a function of environment, microbial respiration, and feedbacks. Biological CH₄ flux from natural and engineered systems is typically represented simply as generation of CH₄ by methanogens minus oxidation by methanotrophs. In many cases, however, CH₄ flux is modulated by transport and solubility mechanisms that occur before oxidation or other chemical transformation. The ability of fungi to directly oxidize CH₄ remains unclear; however, their hydrophobic growths extending above microbial biofilms can improve surface area and sorption of hydrophobic gases. This can improve overall oxidation rates in a biofilm simply by improving phase transfer dynamics and bioavailability to bacterial or archaeal associates. This indirect facilitation is not necessarily intuitive, but there has been a recent emerging interest in harnessing these fungal abilities in engineering bioreactors and filtration systems designed to capture and oxidize CH₄. These dynamics may be playing a similar facilitative role in natural CH₄ oxidation, where fungi may indirectly influence carbon mineralization and methanogen/methanotroph communities, and/or directly oxidize and dissolve gaseous CH₄. This review highlights these unique roles for fungi in determining net CH₄ oxidation rates, and it summarizes the potential to harness fungi to mitigate CH₄ emissions.