(722e) Reversing Methanogenesis to Capture Methane for Liquid Biofuels

The world is rapidly basing much of its economy on methane deposits such as those of the Marcellus Shale in the United States. Although the promise of energy independence is enticing, many of these sites are remote and significant amounts of the methane are released into the atmosphere. This unintended release is detrimental since methane is a potent greenhouse gas, so it is imperative to convert these energy resources efficiently into liquid fuels that may be more readily transported. Since aerobic oxidation of methane is less efficient, we focused on anaerobic processes to capture methane, which are accomplished by anaerobic methanotrophic archaea (ANME) in consortia. However, no pure culture capable of oxidizing and growing on methane anaerobically has been isolated. Here we show methane can be consumed during anaerobic growth, and further converted to liquid fuels, by combining archaeal pathways. Specifically, Methanosarcina acetivorans, an archaeal methanogen, was metabolically engineered to take up methane, rather than to generate it. To capture methane, we cloned the DNA coding for the enzyme methyl-coenzyme M reductase (Mcr) from an unculturable archaeal organism from a Black Sea mat into M. acetivorans to effectively run methanogenesis in reverse. The engineered strain produces primarily acetate, and our results demonstrate that pure cultures can grow anaerobically on methane. Also, we anticipate that our metabolically-engineered strain will provide insights into how methane is cycled in the environment by Archaea as well as will possibly be utilized to convert remote sources of methane into more easily transported biofuels via acetate.