Methanogenic Ethanol Production from Acetate

Abstract

Biological ethanol production is important for the circular carbon economy and makes up 73% of the U.S. biological fuels market. Previously, we produced ethanol by reversing methanogenesis and capturing methane by cloning methyl-coenzyme M reductase (Mcr) from an unculturable population of anaerobic methanotrophic archaea (ANME-1); this process was predicated on the generation of the intermediate acetate and its conversion by the methanogenic host to ethanol. Moreover, methanogens are generally thought to be detrimental for converting acetate to ethanol and are usually intentionally inhibited. Here, we demonstrate for the first time the conversion of acetate as the sole carbon and energy source to both ethanol and methane by the methanogen Methanosarcina acetivorans C2A, resulting in 40% of the metabolized acetate becoming ethanol. Moreover, we found there is 14-fold more ethanol produced from acetate by M. acetivorans C2A compared to that from methane and 5-fold more ethanol compared to M. acetivorans C2A producing ANME-1 Mcr using methane. As expected, we found growth on methanol results primarily in methane generation and low levels of ethanol. Therefore, acetate may be readily converted by the methanogen M. acetivorans to ethanol at high yields, along with methane production.