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.