In the beginning it was dark: Hydrothermal vents and the origin of life (real microbes)

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• William Martin, Universität Düsseldorf
• Thursday 26 November 2015, 16:15-17:15
• Max Perutz Lecture Theatre, Medical Research Council (MRC) (MRC Laboratory of Molecular Biol.

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Life is a chemical reaction. Since life arose, the same exergonic reaction has persisted in uninterrupted continuity right up into this seminar. Life harnesses existing redox couples in such a way that energy is conserved within compartments that are insulated, but not isolated, from the environment, while carbon and nitrogen are assimilated in such a way that more the energy harnessing system ultimately accrues. The talk outlines an energetically feasible path from one, specific hydrothermal setting for the origin of life to the first free-living cells. The sources of energy available to early organic synthesis, early evolving systems and early cells stand in the foreground, as do the possible mechanisms of their conversion into harnessable chemical energy for synthetic reactions. With regard to the possible temporal sequence of events, the talk will focus on: (i) alkaline hydrothermal vents as the far-from-equilibrium setting, (ii) the Wood-Ljungdahl (acetyl-CoA) pathway as the route that could have underpinned carbon assimilation for these processes, (iii) biochemical divergence, within the naturally formed inorganic compartments at a hydrothermal mound, of geochemically confined replicating entities with a complexity below that of free-living prokaryotes, and (iv) acetogenesis and methanogenesis as the ancestral forms of carbon and energy metabolism in the first free-living ancestors of the eubacteria and archaebacteria, respectively. In terms of the main evolutionary transitions in early bioenergetic evolution, the talk will focus on: (i) thioester-dependent substrate-level phosphorylations, (ii) harnessing of naturally existing proton gradients at the vent-ocean interface via the ATP synthase, (iii) harnessing of Na+ gradients generated by H+/Na+ antiporters, (iv) flavin-based bifurcation-dependent gradient generation, and finally (v) quinone-based (and Q-cycle-dependent) proton gradient generation. Of those five transitions, the first four are posited to have taken place at the vent. Ultimately, all bioenergetic processes (hence all life) depend, even in today’s ecosystems, upon low-potential ferredoxins that reduce CO2 . That is a very important observation. Reduced ferredoxin stems in turn either from electron bifurcation or chemiosmosis. At life’s origin, a reaction of the type

reduced iron → reduced carbon

probably stood at the very beginning of bioenergetic processes, hence evolution.

This talk is part of the MRC LMB Seminar Series series.

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