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Life on the thermodynamic edge: Respiratory growth of an acetotrophic methanogen

D. Prakash,Shikha S. Chauhan,J. Ferry

Published 2019 in Science Advances

ABSTRACT

Respiration is key to growth of acetotrophic Archaea that generate most of the 109 metric-ton annual production of methane. Although two-thirds of the nearly 1 billion metric tons of methane produced annually in Earth’s biosphere derives from acetate, the in situ process has escaped rigorous understanding. The unresolved question concerns the mechanism by which the exceptionally marginal amount of available energy supports acetotrophic growth of methanogenic archaea in the environment. Here, we show that Methanosarcina acetivorans conserves energy by Fe(III)-dependent respiratory metabolism of acetate, augmenting production of the greenhouse gas methane. An extensively revised, ecologically relevant, biochemical pathway for acetotrophic growth is presented, in which the conservation of respiratory energy is maximized by electron bifurcation, a previously unknown mechanism of biological energy coupling. The results transform the ecological and biochemical understanding of methanogenesis and the role of iron in the mineralization of organic matter in anaerobic environments.

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