On the inevitable journey to being
Dr Michael Russell, JPL, California Institute of Technology
Abstract
Life is the evolutionary culmination of emergent symmetry-breaking, macroscopically organized dynamic structures in the universe. Members of this cascading series of autocatalytic energy converting systems, or engines in Cottrell’s terminology, become ever more complex—more chemical and less physical—as each engine extracts, exploits and generates ever lower grades of energy and resources in the service of entropy generation. Each one of these engines emerges spontaneously from order created by a particular mother engine or engines as the disequilibrated potential daughter is driven beyond a critical point, as in e.g., the transition to thermonuclear reactions during gravitationally-driven star formation; the transition to convective flow in systems driven beyond the Rayleigh limit by thermal gradients (such as those responsible for the tectonic dynamics of our planet); and the onset of Mohr-Coulomb failure and fracture propagation due to differential mechanical stress exceeding rock strength (as occurs in the planet's tectonically-strained ocean floor rock). Importantly, it is these fractures in the ocean floor, acting themselves as engines of dissipation, that allow ocean water access to the crust which in turn drives the onset of exothermic serpentinization, alkaline hydrothermal convection and thereby the spontaneous production of precipitated submarine hydrothermal mounds. It is at such mounds finally that, we argue, the two chemical disequilibria directly causative in the emergence of life spontaneously arose across the mineral precipitate membranes separating the acidulous, nitrate-bearing CO2-rich, Hadean sea from the alkaline and CH4/H2-rich serpentine-generated effluents. The first and foremost of these great geochemical gifts was the imposition of essential redox gradients involving hydrothermal CH4 and H2 as electron donors, and CO2 and nitrate, nitrite, and ferric iron from the ambient ocean as acceptors; which gradients, we propose, functioned as the original “carbon-fixing engine”. The second gift, also imposed across the inorganic membrane, was a post-critical-point (milli)voltage pH potential (proton concentration gradient) that, we hypothesize, drove the condensation of orthophosphate to produce a high energy currency:- “the pyrophosphatase engine”. Notably, of course, this specific ionic gradient, there available for the taking, is one upon which all extant cellular systems now depend even though they must constantly recreate it on their own through the harnessing of redox gradients, or the catabolism of biomolecules such as glucose, to recondense ADP to ATP. Once metabolizing cells emerged and evolved in this submarine mound, the call for constant and far-from-equilibrium free energy sources presumably diminished somewhat due to the relative stability, and “templating effect” of the relatively stable organized states of matter mediating the key steps of proto-life free energy conversion. Thus the metabolic engines could sustain themselves by merely “ticking over” during times of deprivation and in this way more robustly survive for the long periods that life occupied the ocean floor and deep biosphere before its escape to the wider and more free-energy rich world and, ultimately, its “discovery” of photosynthesis.
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Dr Michael Russell, JPL, California Institute of Technology
Dr Michael Russell, JPL, California Institute of Technology
"Dr Michael Russell is a Research Scientist at the Jet Propulsion Laboratory, California Institute of Technology where he is testing his theory on the emergence of life. His life has come full circle from his first job as a works chemist in East London, testing the activity of nickel catalysts for organic synthesis. He then attended the University of London, studying geology, chemistry and physics. From London he was posted to the Solomon Islands Geological Survey to search for submarine hot springs and explore for mineral deposits. He continued this latter activity in Canada before returning to the University of Durham in the UK to undertake research on the newly discovered giant mineral deposits in Ireland. Thereafter he joined the staff at the University of Strathclyde in Glasgow, Scotland, while continuing his research in Ireland—research that led to his theorizing into the emergence of life at submarine springs. He transferred to the University of Glasgow in 1990 and to JPL in 2006. In June 2009 he was awarded the William Smith Medal from the Geological Society of London for his lifetime contribution to applied geology."
The energetics of organic synthesis inside and outside the cell
Professor Jan Amend, University of Southern California
Abstract
Thermodynamic modeling of organic synthesis has largely been focused on deep-sea hydrothermal systems. When seawater mixes with hydrothermal fluids, redox gradients are established that serve as potential energy sources for the formation of organic compounds and biomolecules from inorganic starting materials. This energetic drive, which varies substantially depending on the type of host rock, is present and available both for abiotic (outside the cell) and biotic (inside the cell) processes. Here, we review and synthesize a library of theoretical studies that target organic synthesis energetics. The biogeochemical scenarios evaluated include those in present-day hydrothermal systems and in putative early Earth environments. It is consistently and repeatedly shown in these studies that the formation of relatively simple organic compounds and biomolecules can be energy-yielding (exergonic) at conditions that occur in hydrothermal systems. Expanding on our ability to calculate biomass synthesis energetics, we also present here a new approach for estimating the energetics of polymerization reactions, specifically those associated with polypeptide formation from the requisite amino acids.
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Professor Jan Amend, University of Southern California
Professor Jan Amend, University of Southern California
"Jan Amend is a Professor of Microbial Geochemistry in the Departments of Earth Sciences and Biological Sciences at the University of Southern California. He earned his Ph.D. in 1995 from the University of California, Berkeley under the mentorship of Harold Helgeson. After post-doctoral fellowships with John Baross (University of Washington) and Everett Shock (Washington University), Amend joined the faculty of the Department of Earth and Planetary Sciences at Washington University. There, he was Assistant Professor, Associate Professor, and Director of the Environmental Studies Program until his move to Los Angeles in 2011. Amend’s research combines field work in hydrothermal systems, theoretical geochemistry, and laboratory experimentation in attempts to better understand the microbiology/geochemistry interface. Of particular interests are the energetics of microbial metabolism in extreme environments, the deep subsurface biosphere, microbial community structures and metabolic activity in shallow-sea hydrothermal systems, cultivation of novel thermophilic archaea and bacteria, environmental microbiology of arsenic, and life detection with a focus on astrobiology."
The early evolution of biological energy conservation: hydrogen, metals, gradients and electron bifurcation
Professor William Martin, Heinrich Heine University, Germany
Abstract
In very early chemical evolution, the forerunners of carbon and energy metabolism were the processes of generating reduced carbon compounds from carbon dioxide and the mechanisms of harnessing energy as compounds capable of doing some chemical work. New insights into energy conservation in methanogens and acetogens — cells that fuel both their carbon and energy metabolism through the CO2/H2 redox couple — suggest that reduced ferredoxin is the most ancient biological energy currency. Those anaerobic autotrophs generate reduced ferredoxin from H2 via a mechanism called electron bifurcation, a process that in turn links ferredoxin reduction to exergonic reactions and the generation of transmembrane ion gradients. Overall carbon and energy metabolsm in methanogens and acetogens that lack cytochromes and quinones (or the quinone analogue methanophenazine) involves Ech and Rnf complexes that pump ions while reducing protons and NAD+, respectively, with electrons from ferredoxin. This has some similarity to serpentinization, a geochemical process in which electons from Fe2+ generate H2 and reduced carbon compounds such as methane. The new findings from microbial physiology are remarkably congruent with the independently derived idea that life evolved in submarine alkaline hydrothermal vents and underscore evolutionarily significant similarities as well as differences in acetogen and methanogen physiology.
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Professor William Martin, Heinrich Heine University, Germany
Professor William Martin, Heinrich Heine University, Germany
Bill Martin received his undergraduate degree in Biology at the University of Hannover in 1985 and completed his PhD in Genetics with Heinz Saedler at the Max Planck Institute for Breeding Research in Cologne in 1988. He pursued postdoctoral research with Rüdiger Cerff at the University of Braunschweig on the origins and evolution of eukaryotes and their bioenergetic organelles (chloroplasts and mitochondria). In 1999 he accepted the position of full professor at the University of Düsseldorf. His biochemical work focusses on energy metabolism in eukaryotic anaerobes and the role of hydrogenosomes — hydrogen-producing forms of mitochondria — therein. His genome evolutionary work focusses on non-treelike evolutionary processes such as gene transfers from organelles to the nucleus (endosymbiotic gene transfer) and lateral gene transfer among prokaryotes, the study of which incorporates networks to recover the vertical and the horizontal components of genome evolution.
A reassessment of autotrophy at the emergence of life
Professor Wolfgang Nitschke, CNRS Marseilles
Abstract
An empirical way to study the origin of life is through extrapolating the evolutionary history of extant life back towards its very beginning while respecting geochemical boundary conditions and fundamental physical laws. This approach has in the past identified the Wood-Ljungdahl (WL) pathway of aceto- and methanogens as a promising candidate for primordial energy and carbon metabolism. However, a number of problems with this scenario have recently been pointed out (Schoepp et al., 2012, Biochim.Biophys.Acta, doi: 10.1016/j.bbabio.2012.09.005) suggesting that the original model may require amendments and reinterpretations. Here we present a scenario which stipulates that methane and nitrogen oxyanions ought to be considered in addition to the canonical WL-substrates, H2 and CO2. The recently described denitrifying methanotrophs represent an extant example for a corresponding metabolism. We will present arguments suggesting that denitrifying methanotrophy may pre-date aceto- and methanogenesis. Extant methanotrophic pathways suggest that the earliest carbon-fixing and energy harvesting metabolism may have condensed CO (delivered by the Ni/Fe-catalysed reduction of CO2) and a second C1-body represented by formaldehyde (or a sulphur-associated methyl group) produced by monooxygenation of methane to methanol (at a diiron centre) followed by further oxidation to formaldehyde (possibly catalysed by a molybdenum/tungsten-sulphide). In both half-reactions, redox bifurcations play crucial roles.
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Professor Wolfgang Nitschke, CNRS Marseilles
Professor Wolfgang Nitschke, CNRS Marseilles
"Following a Master’s degree in Physics Wolfgang Nitschke obtained his PhD in Biochemistry and Biophysics from the University of Regensburg/Germany in 1987. He then spent periods of post-doctoral research at the CEA in Saclay/France, the Institut de Biologie Physico-Chimique in Paris/France and the University of Freiburg/Germany. He has been at the Laboratoire de Bioénergétique et Ingénierie des Protéines (CNRS) in Marseilles/France since 1995 and is presently leading the research group ""Evolution of Bioenergetics"" at the institute. Their research topic aims to elucidate the evolutionary pathways of specific bioenergetic electron transfer chains through the last 4 billion years of life on Earth, i.e. from the Last Universal Common Ancestor (LUCA) to extant organisms."