Radiolytically reworked Archean organic matter in a habitable deep ancient high-temperature brine

Investigations of abiotic and biotic contributions to dissolved organic carbon (DOC) are required to constrain microbial habitability in continental subsurface fluids. Here we investigate a large (101-283 mg C/L) DOC pool in an ancient (>1Ga), high temperature (45-55 °C), low biomass (102-104 cells/mL), and deep (3.2 km) brine from an uranium-enriched South African gold mine. Excitation-emission matrices (EEMs), negative electrospray ionization (-ESI) 21 tesla Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), and amino acid analyses suggest the brine DOC is primarily radiolytically oxidized kerogen-rich shales or reefs, methane and ethane, with trace amounts of C3-C6 hydrocarbons and organic sulfides. δ2H and δ13C of C1-C3 hydrocarbons are consistent with abiotic origins. These findings suggest water-rock processes control redox and C cycling, helping support a meagre, slow biosphere over geologic time. A radiolytic-driven, habitable brine may signal similar settings are good targets in the search for life beyond Earth.

Testing Abiotic Reduction of NAD+ Directly Mediated by Iron/Sulfur Minerals

Life emerged in a geochemical context, possibly in the midst of mineral substrates. However, it is not known to what extent minerals and dissolved inorganic ions could have facilitated the evolution of biochemical reactions. Herein, we have experimentally shown that iron sulfide minerals can act as electron transfer agents for the reduction of the ubiquitous biological protein cofactor nicotinamide adenine dinucleotide (NAD⁺) under anaerobic prebiotic conditions, observing the NAD⁺/NADH redox transition by using ultraviolet-visible spectroscopy and ¹H nuclear magnetic resonance. This reaction was mediated with iron sulfide minerals, which were likely abundant on early Earth in seafloor and hydrothermal settings; and the NAD⁺/NADH redox reaction occurred in the absence of UV light, peptide ligand(s), or dissolved mediators. To better understand this reaction, thermodynamic modeling was also performed. The ability of an iron sulfide mineral to transfer electrons to a biochemical cofactor that is found in every living cell demonstrates how geologic materials could have played a direct role in the evolution of certain cofactor-driven metabolic pathways.

A Proposed Geobiology-Driven Nomenclature for Astrobiological In Situ Observations and Sample Analyses

As the exploration of Mars and other worlds for signs of life has increased, the need for a common nomenclature and consensus has become significantly important for proper identification of nonterrestrial/non-Earth biology, biogenic structures, and chemical processes generated from biological processes. The fact that Earth is our single data point for all life, diversity, and evolution means that there is an inherent bias toward life as we know it through our own planet's history. The search for life "as we don't know it" then brings this bias forward to decision-making regarding mission instruments and payloads. Understandably, this leads to several top-level scientific, theoretical, and philosophical questions regarding the definition of life and what it means for future life detection missions. How can we decide on how and where to detect known and unknown signs of life with a single biased data point? What features could act as universal biosignatures that support Darwinian evolution in the geological context of nonterrestrial time lines? The purpose of this article is to generate an improved nomenclature for terrestrial features that have mineral/microbial interactions within structures and to confirm which features can only exist from life (biotic), features that are modified by biological processes (biogenic), features that life does not affect (abiotic), and properties that can exist or not regardless of the presence of biology (abiogenic). These four categories are critical in understanding and deciphering future returned samples from Mars, signs of potential extinct/ancient and extant life on Mars, and in situ analyses from ocean worlds to distinguish and separate what physical structures and chemical patterns are due to life and which are not. Moreover, we discuss hypothetical detection and preservation environments for extant and extinct life, respectively. These proposed environments will take into account independent active and ancient in situ detection prospects by using previous planetary exploration studies and discuss the geobiological implications within an astrobiological context.

3D Printed Minerals as Astrobiology Analogs of Hydrothermal Vent Chimneys

Hydrothermal vents, which are highly plausible habitable environments for life and of interest for some origin-of-life scenarios, may exist on icy moons such as Europa or Enceladus in addition to Earth. Some hydrothermal vent chimney structures are extremely porous and friable, making their reconstruction in the lab challenging (e.g., brucite or saponite in alkaline hydrothermal settings). Here, we present the results from our efforts to reconstruct a simplified chimney structure directly out of mineral powder using binder jet additive manufacturing. Olivine sand was chosen for this initial method development effort since it represents a naturally occurring seafloor material and is inexpensively available in large quantities in powder form. The crystal structure of olivine used for the print was not modified during the process, as confirmed by powder X-ray diffraction (XRD). To characterize the microstructure of our 3D printed precipitates, we used computed tomography (CT) X-ray scan techniques. We also evaluated a chimney precipitate from a sample collected from the Prony Hydrothermal Field (PHF), southern New Caledonia, an alkaline system driven by serpentinization with mineralogy composed of brucite and carbonates. While not directly comparable from a mineralogical point of view, the microstructure and porosity of both precipitates was similar, suggesting that our 3D printing technique may be a valuable tool for future astrobiology research on hydrothermal vent precipitates.

Metabolomics as an Emerging Tool in the Search for Astrobiologically Relevant Biomarkers

It is now routinely possible to sequence and recover microbial genomes from environmental samples. To the degree it is feasible to assign transcriptional and translational functions to these genomes, it should be possible, in principle, to largely understand the complete molecular inputs and outputs of a microbial community. However, gene-based tools alone are presently insufficient to describe the full suite of chemical reactions and small molecules that compose a living cell. Metabolomic tools have developed quickly and now enable rapid detection and identification of small molecules within biological and environmental samples. The convergence of these technologies will soon facilitate the detection of novel enzymatic activities, novel organisms, and potentially extraterrestrial life-forms on solar system bodies. This review explores the methodological problems and scientific opportunities facing researchers who hope to apply metabolomic methods in astrobiology-related fields, and how present challenges might be overcome.

Exploring, Mapping, and Data Management Integration of Habitable Environments in Astrobiology

New approaches to blending geoscience, planetary science, microbiology-geobiology/ecology, geoinformatics and cyberinfrastructure technology disciplines in a holistic effort can be transformative to astrobiology explorations. Over the last two decades, overwhelming orbital evidence has confirmed the abundance of authigenic (in situ, formed in place) minerals on Mars. On Earth, environments where authigenic minerals form provide a substrate for the preservation of microbial life. Similarly, extraterrestrial life is likely to be preserved where crustal minerals can record and preserve the biochemical mechanisms (i.e., biosignatures). The search for astrobiological evidence on Mars has focused on identifying past or present habitable environments - places that could support some semblance of life. Thus, authigenic minerals represent a promising habitable environment where extraterrestrial life could be recorded and potentially preserved over geologic time scales. Astrobiology research necessarily takes place over vastly different scales; from molecules to viruses and microbes to those of satellites and solar system exploration, but the differing scales of analyses are rarely connected quantitatively. The mismatch between the scales of these observations- from the macro- satellite mineralogical observations to the micro- microbial observations- limits the applicability of our astrobiological understanding as we search for records of life beyond Earth. Each-scale observation requires knowledge of the geologic context and the environmental parameters important for assessing habitability. Exploration efforts to search for extraterrestrial life should attempt to quantify both the geospatial context and the temporal/spatial relationships between microbial abundance and diversity within authigenic minerals at multiple scales, while assimilating resolutions from satellite observations to field measurements to microscopic analyses. Statistical measures, computer vision, and the geospatial synergy of Geographic Information Systems (GIS), can allow analyses of objective data-driven methods to locate, map, and predict where the "sweet spots" of habitable environments occur at multiple scales. This approach of science information architecture or an "Astrobiology Information System" can provide the necessary maps to guide researchers to discoveries via testing, visualizing, documenting, and collaborating on significant data relationships that will advance explorations for evidence of life in our solar system and beyond.

MR vs CT in progressive supranuclear palsy

Nine progressive supranuclear palsy (PSP) patients were studied with computerized tomography (CT) and magnetic resonance (MR) in order to determine the efficacy of each in detecting atrophy of the brainstem. Three additional PSP patients were evaluated with MRI for quantitative (electronic) measurements of the colliculi, pons and midbrain tegmentum. Both CT and MRI were equally effective in demonstrating midbrain atrophy. The MR was able to utilize the sagittal view to visualize thinning of the collicular (quadrigeminal) plate, a useful sign in PSP. Atrophy of the thinned collicular plate is more pronounced in the superior colliculus, one of the most common sites of pathology in PSP. The MR is able to make quantitative measurements of the degree of atrophy of the colliculi, pons and midbrain tegmentum.