( ly energy sources has largely been igno...)Methane-belching bugs inspire a new theory of the origin of life on Earth

ly energy sources has largely been ignored by the classical origin-of-life field," Molecular Biology and Evolution's Martin says, "which has largely been the domain of chemists. But microbiologists are the only ones who understand where the origin of life needs to get--modern microbial life."

According to the heterotrophic theory, a primordial soup of simple molecules arose first, driven by nonbiological energy sources like lightning, and led eventually to primitive life forms. One difficulty with this theory is due to the huge variety and complexity of organic molecules that would have had to arise spontaneously. In contrast, the chemoautotrophic theory rests on the idea that primitive life forms themselves, perhaps associated with catalytic iron and sulfur minerals, gave rise to the first simple biological molecules. The obstacles to this theory are the large number of steps in the biochemical cycles that have been suggested, and the staggering structural complexity of the only known enzyme complexes that drive those reactions. Debate between the two camps has raged for two decades.

By studying a microbe that Ferry discovered thriving in the oxygen-free, carbon-monoxide-rich sediment beneath kelp beds, he and his group have helped to break this impasse. Life may have emerged in just such an environment, and this microbe's unique biochemistry may harbor the molecular fossil of the first metabolism on Earth.

While other microbes make methane from carbon monoxide, this particular species (one "Methanosarcina acetivorans") also produces acetate--better known as vinegar. Ferry and House, in collaboration with Barry Karger at Northeastern University, showed how carbon monoxide is converted to acetate in a biochemical pathway that includes a well-known pair of enzymes, called Pta ("phosphotransacetylase") and Ack ("acetate kinase"). The two researchers realized that, in the presence of minerals containing iron sulfides, acetate could have been cat
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Source:Penn State

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