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Home , Geochemistry, Ion, Redox

Speaker: Dr. Laura Barge NASA Institute / Jet Propulsion Laboratory (USA)

Presentation abstract:

The Fuel Model of : A New Approach to Origin- of-Life Simulations

I will discuss how the chemiosmotic theory for the origin of life can be modeled as a , and how laboratory simulations of the origin of life in general can benefit from this systems-led approach. We term this the “prebiotic fuel cell” (PFC) operating at a putative Hadean , and I will present preliminary results utilizing electrochemical analysis techniques and exchange membrane (PEM) fuel cell components to test the properties of this and other geo-electrochemical systems. The modular of fuel cells makes them ideal for creating geo-electro-chemical reactors to simulate hydrothermal systems on wet rocky and characterize the energetic properties of the seafloor / hydrothermal interface. That electrochemical techniques should be applied to simulating the origin of life follows from the recognition of the fuel cell-like properties of pre-biotic chemical systems and the earliest . Conducting this type of laboratory simulation of the emergence of bioenergetics will not only be informative in the context of the origin of life on , but may help us understand whether it is possible for life to have emerged in similar environments on other worlds. The operations of extant life are analogous to those of a fuel cell, and some version of the fundamental components that make the biological fuel cell function (ATP-synthase; -selective membranes maintaining pH / electrical gradients; the transport chain) were also likely present in the last universal common ancestor (Gogarten et al., 1989; Martin and Russell, 2007; Mulkidjanian et al. 2007; Schoepp-Cothenet et al., 2013). Hydrothermal vents are “environmental fuel cells” (Yamamoto et al., 2013) since electrical and pH potentials can be generated where reduced hydrothermal fluids interface the more oxidizing (Russell and Hall 1997, 2006), and these geochemical potentials can be maintained and mediated across physical boundaries, e.g. electrically conductive biofilms, or an inorganic chimney precipitate (e.g. Nakamura et al., 2010; Yamamoto et al., 2013). The electrochemical polarities driving microbial bioenergetics are somewhat similar to those obtained at hydrothermal vents, with variations occurring mostly in the details of electron flow and the substrates (Nitschke and Russell, 2009; El-Naggar et al., 2010). Because we consider that the LUCA (last universal common ancestor) – the last unified biochemical system arising from – also had these basic fuel cell properties (Russell and Hall 1997; Nitschke and Russell 2009; cf. Huang et al., 2012, Lane and Martin, 2012), we suggest that some key steps at the origin of metabolism may then be simulated experimentally within the context of the architecture of a fuel cell. The fuel cell represents a holistic chemical system which is understood, amenable to computational modeling, and open to sophisticated analytical diagnostics. It is a systems approach that has not yet been exploited experimentally within the sphere of abiogenesis yet offers a potentially powerful theoretical and experimental model through which to explore such emergent physicochemical systems. We will detail the components of what we have termed the “prebiotic fuel cell” (PFC) operating at a putative Hadean hydrothermal vent that incorporates the available geochemical ingredients of the early Earth and fulfills the requirements of early microbial bioenergetics (Schoepp-Cothenet et al., 2013). The membranes formed at the interface of contrasting in our experiments represent specific components that would have been contained within the larger, - and silica-containing precipitates formed at an alkaline hydrothermal vent on the early Earth. Iron sulfide precipitates, formed in pH / ion gradients via diffusion and self-assembly, could contribute to the electrocatalytic properties of a hydrothermal chimney if they were capable of electron conduction. These preliminary experiments reveal that self-assembling inorganic precipitate membranes analogous to components in hydrothermal chimneys have many unusual properties (van Oss 1984) that may be biologically and/or prebiotically relevant, probably including preferential ion-exchange, charged surfaces that could maintain ion membrane potentials, and/or electrical conductivity. In some ways, the inorganic Fe/S precipitates formed on cloth in our interface experiments are similar to the ion-exchange membranes and diffusion layers in commercial as well as experimental fuel cells (Kim et al. 2009; Paulo and Tavares 2011). This preliminary success of using commercially available fuel cell /GDL material (carbon cloth) as a template to precipitate simulated hydrothermal mineral catalysts is quite promising, as these can be directly used in PEM fuel cell assemblies to catalyze redox reactions in a pressurized out-of-equilibrium test-bed reactor. Considering that 1) microbes and mitochondria are highly evolved biological fuel cells, and 2) that the earliest life on Earth was chemiosmotic, chemosynthetic and utilized sources commonly found in modern alkaline hydrothermal vents, it is clear why hydrothermal vents are theorized as a likely environment for the origin of life. Our preliminary experiments were successful in forming putative electro-catalytic in out-of-equilibrium chemical systems, simulating the formation of sulfide precipitates at the These methods utilized in this work are easily generalized to other geochemical interfaces of interest, such as - reactions on early or the icy . Moving toward this type of laboratory simulation of the emergence of bioenergetics will not only be informative in the context of the origin of life on Earth, but may help us understand whether it is possible for life to have emerged in similar environments on other planets.