Crystal Habits as Potential Biosignatures.

Our understanding of crystalline structures within terrestrial planetary analog environments can shed light on how these features can be interpreted on rocky planets and icy moons in our solar system. The ability to distinguish biogenic and abiotic components within the mineral, crystal, and structural features allows us to inform future life detection missions, science payloads, and instrument measurement resolutions. Moreover, having these terrestrial reference measurements in a review format allows the measurement rationale to be understood in the context of mission concepts and geomicrobiological assessment of life in extreme environments.

Laminae as Potential Biosignatures.

Laminae are millimeter-scale features in rocks created by physiochemical processes that can be influenced by the presence and activities of communities of organisms that occur as biofilms and microbial mats. The structure and composition of laminae reflect the processes involved in their formation and can be preserved in the rock record over geologic time; however, diagenetic and metamorphic alteration can lead to the loss of primary information and confusion over the interpretation of their origins. As potential records of ancient life, laminae can preserve evidence of microbial activity over billions of years of Earth's history.

Structural Biosignatures-A Category of Potential Biosignatures in the Life Detection Knowledge Base.

The Life Detection Knowledge Base (LDKB) is part of the Life Detection Forum suite of web tools developed for life detection mission planners. This article details the development of one of its categories of biosignatures, the category. The category includes physical attributes of objects and their spatial relationships (e.

Radiolytic support for oxidative metabolism in an ancient subsurface brine system.

Long-isolated subsurface brine environments (Ma-Ga residence times) may be habitable if they sustainably provide substrates, e.g. through water-rock reactions, that support microbial catabolic energy yields exceeding maintenance costs.

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 (10-10 cells/mL), and deep (3.2 km) brine from an uranium-enriched South African gold mine.

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 H nuclear magnetic resonance.

A Proposed Geobiology-Driven Nomenclature for Astrobiological 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.

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 ( 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.

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.

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

[This corrects the article DOI: 10.3389/fmicb.2019.