Electromethanogenesis: the direct bioconversion of current to methane
DAVID JONES, PENNSYLVANIA STATE UNIVERSITY
physiologists Alfons Stams and Jeacould then be stored as fuel for Bruce Logan and co-workers at nine Geelhoed at Wageningen Unilater use, says Logan. Pennsylvania State University versity (The Netherlands). Stams At the moment, you can make have found that a microbe, most and Geelhoed note that, in the curbiofuels from about anything likely Methanobacterium palustre, rent paper, the authors’ interpretathat’s biodegradable, but it’s a can synthesize methane using tion of their results is based on the complex process, explains Logan. electrons directly from current in observation that little or no hydroTo make methane electrochemiaddition to using hydrogen gas gen is produced in a similar setup cally directly from CO2 is difficult (DOI 10.1021/es803531g). This fundamental discovery because there is a big could lead to an efficient overpotential. But methaway to generate methane, nogens can do it very easthe main component of ily and have been for natural gas, from electriceons. What the paper imity and could have other plies is this: if you have a environmental source of current, you applications. have a source of electrons, Despite its name, M. and you can make methpalustre is not a bacterium ane electrochemically. but an archaeon. It is also “Let’s say the sun is shina methanogen, which ing during the day, and you means it can reduce CO2 to are making solar energy, great! Then nighttime methane with H2 as an comes; what do you do?” electron donor. Now, Loasks Logan. “If you had a gan and colleagues have Researchers Shaoan Cheng, Bruce Logan, and Defeng Xing big capacitor or battery you found that this microbe (left to right) examine a two-chamber microbial electrolycould store the energy, or appears to use electrons sis reactor. you could make a fuel like from current. “We think hydrogen or methane. this is the first direct eviwithout microorganisms. Although Some people say hydrogen is too dence that methanogens can acthe authors show convincingly that difficult to compress and to store, cept electrons,” says Logan. methanogens are essential, Stams [but] nobody says that about natu“Efficient methane production and Geelhoed believe that the ral gas. We’ve got pipelines of natufueled by electrons directly from an study does not unequivocally rule ral gas all over the world, and it’s electrode is an important discovout the possibility that hydrogen is used in conventional engines. It’s ery!” says Yuri Gorby, who studies formed first and is the electron dono problem to use at all,” Logan electrically conductive appendages nor for CO2 reduction. They note concludes. produced by bacteria (know as Korneel Rabaey, who is at the bacterial nanowires) at the J. Craig that bacterial and/or archaeal enUniversity of Queensland (AustraVenter Institute in San Diego. zymes may mediate electron translia) and is an expert on bioelectri“What is significant about this pubfer between the electrode surface cal systems, believes that while lication is the reported efficiency of and cells. They also suggest that a the discovery that methanogenic energy transformation; 80% effipossible role for hydrogen could be archaea can perform extracellular ciency is pretty darn good. As a miruled out experimentally by using a electron transfer is exciting, it’s crobial physiologist and ecologist, compound that inhibits methanomainly interesting from a scienthe questions become, ‘What is the genesis. “Further research is clearly tific rather than a practical viewmechanism, and does this occur in necessary to obtain insight of the point. The next step is to nature?’ Although this article does molecular mechanism of elecdemonstrate this with an isolated not address these questions, it protromethanogenesis and electrohymethanogen, and that is a worthvides hope that it is at least posdrogenesis,” they say. while challenge, according to Rasible.” The direct transfer of electrical baey. Logan’s group is already “Methanogenic archaea have a current, or more precisely, elecworking on it. unique biochemistry, employing trons, to methanogens suggests cofactors and enzymes not comthat it may be possible to gener—BARBARA BOOTH monly present in other types of ate methane from wind or solar microorganisms,” explain microbial power sources; the methane
10.1021/es901126e
2009 American Chemical Society
Published on Web 05/20/2009
July 1, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 4619
