Secondary Electrons as an Energy Source for Life

Abstract

Life on Earth is found in a wide range of environments as long as the basic requirements of a liquid solvent, a nutrient source, and free energy are met. Previous hypotheses have speculated how extraterrestrial microbial life may function, among them that particle radiation might power living cells indirectly through radiolytic products. On Earth, so-called electrophilic organisms can harness electron flow from an extracellular cathode to build biomolecules. Here, we describe two hypothetical mechanisms, termed "direct electrophy" and "indirect electrophy" or "fluorosynthesis," by which organisms could harness extracellular free electrons to synthesize organic matter, thus expanding the ensemble of potential habitats in which extraterrestrial organisms might be found in the Solar System and beyond. The first mechanism involves the direct flow of secondary electrons from particle radiation to a microbial cell to power the organism. The second involves the indirect utilization of impinging secondary electrons and a fluorescing molecule, either biotic or abiotic in origin, to drive photosynthesis. Both mechanisms involve the attenuation of an incoming particle's energy to create low-energy secondary electrons. The validity of the hypotheses is assessed through simple calculations showing the biomass density attainable from the energy supplied. Also discussed are potential survival strategies that could be used by organisms living in possible habitats with a plentiful supply of secondary electrons, such as near the surface of an icy moon. While we acknowledge that the only definitive test for the hypothesis is to collect specimens, we also describe experiments or terrestrial observations that could support or nullify the hypotheses. Key Words: Radiation-Electrophiles-Subsurface life. Astrobiology 18, 73-85.

Nanoscale Tungsten-Microbial Interface of the Metal Immobilizing Thermoacidophilic Archaeon Metallosphaera sedula Cultivated With Tungsten Polyoxometalate

“…How would a microbe with metal-oxidizing metabolic activity decompose tungsten POM that contains tungsten in the highest oxidation state of 6 + ? Microorganisms such as metal oxidizers can utilize a mechanism to respire directly on electron flow under the conditions where electron donor is available (Choi and Sang, 2016; Stelmach et al, 2018). The cultivation and growth of M. sedula occurs in single medium of complex composition with a number of parameters (e.g., acidic pH, elevated temperature, ionic strength, pressures of gas phases), which can upraise the appearance of green or blue reduced W-POM species, affecting the ratio of addendum W 6+ /W 5+ and thus stimulating electron circulation within one single molecule of W-POM.…”

Identifying the Molecular Orientation and Clusters in the Liquid–Vapor Interface of 1-Propanol by Time-Delayed Mass Spectrometry

“…Applications of the electron-driven or -induced chemical reactions in the liquid surface 29 are also promising, particularly for a fundamental topic such as the origin of life substances. 30 ■ ASSOCIATED CONTENT * sı Supporting Information…”

Subsurface exolife

“…In addition to these putative ecosystems, life may derive energy from electrical currents by means of electron-transfer reactions, where the electrons are supplied from the magnetospheres of giant planets, and this process has been dubbed ‘direct electrophy’ (Stelmach et al , 2018). It should be recognized that this near-surface ecosystem would be feasible only for (type B) moons orbiting giant planets.…”

“…It should be recognized that this near-surface ecosystem would be feasible only for (type B) moons orbiting giant planets. Using the data tabulated in Figure 2 and Table 1 of Stelmach et al (2018), the maximum steady-state biomass is given by where Φ e represents the electron number flux (units of m −2 s −1 ) received at the surface of the moon, assuming that the average energy of the particles is approximately 0.5 MeV.…”

“…Using the data tabulated in Fig. 2 and Table 1 of Stelmach et al (2018), the maximum steady-state biomass is given by…”