Immunoanalytical Approach for Detecting and Identifying Ancestral Peptide Biomarkers in Early Earth Analogue Environments

Several mass spectrometry and spectroscopic techniques have been used in the search for molecular biomarkers on Mars. A major constraint is their capability to detect and identify large and complex compounds such as peptides or other biopolymers. Multiplex immunoassays can detect these compounds, but antibodies must be produced for a large number of sequence-dependent molecular targets. Ancestral Sequence Reconstruction (ASR) followed by protein "resurrection" in the lab can help to narrow the selection of targets. Herein, we propose an immunoanalytical method to identify ancient and universally conserved protein/peptide sequences as targets for identifying ancestral biomarkers in nature. We have developed, tested, and validated this approach by producing antibodies to eight previously described ancestral resurrected proteins (three β-lactamases, three thioredoxins, one Elongation Factor Tu, and one RuBisCO, all of them theoretically dated as Precambrian), and used them as a proxy to search for any potential feature of them that could be present in current natural environments. By fluorescent sandwich microarray immunoassays (FSMI), we have detected positive immunoreactions with antibodies to the oldest β-lactamase and thioredoxin proteins (ca. 4 Ga) in samples from a hydrothermal environment. Fine epitope mapping and inhibitory immunoassays allowed the identification of well-conserved epitope peptide sequences that resulted from ASR and were present in the sample. We corroborated these results by metagenomic sequencing and found several genes encoding analogue proteins with significant matches to the peptide epitopes identified with the antibodies. The results demonstrated that peptides inferred from ASR studies have true counterpart analogues in Nature, which validates and strengthens the well-known ASR/protein resurrection technique and our immunoanalytical approach for investigating ancient environments and metabolisms on Earth and elsewhere.

Prokaryotic Community Structure and Metabolisms in Shallow Subsurface of Atacama Desert Playas and Alluvial Fans After Heavy Rains: Repairing and Preparing for Next Dry Period

The Atacama Desert, the oldest and driest desert on Earth, displays significant rains only once per decade. To investigate how microbial communities take advantage of these sporadic wet events, we carried out a geomicrobiological study a few days after a heavy rain event in 2015. Different physicochemical and microbial community analyses were conducted on samples collected from playas and an alluvial fan from surface, 10, 20, 50, and 80 cm depth. Gravimetric moisture content peaks were measured in 10 and 20 cm depth samples (from 1.65 to 4.1% w/w maximum values) while, in general, main anions such as chloride, nitrate, and sulfate concentrations increased with depth, with maximum values of 13-1,125; 168-10,109; and 9,904-30,952 ppm, respectively. Small organic anions such as formate and acetate had maximum concentrations from 2.61 to 3.44 ppm and 6.73 to 28.75 ppm, respectively. Microbial diversity inferred from DNA analysis showed Actinobacteria and Alphaproteobacteria as the most abundant and widespread bacterial taxa among the samples, followed by Chloroflexi and Firmicutes at specific sites. Archaea were mainly dominated by Nitrososphaerales, Methanobacteria, with the detection of other groups such as Halobacteria. Metaproteomics showed a high and even distribution of proteins involved in primary metabolic processes such as energy production and biosynthetic pathways, and a limited but remarkable presence of proteins related to resistance to environmental stressors such as radiation, oxidation, or desiccation. The results indicated that extra humidity in the system allows the microbial community to repair, and prepare for the upcoming hyperarid period. Additionally, it supplies biomarkers to the medium whose preservation potential could be high under strong desiccation conditions and relevant for planetary exploration.

Subsurface Microbial Habitats in an Extreme Desert Mars-Analog Environment

Sediments in the hyper-arid core of the Atacama Desert are a terrestrial analog to Mars regolith. Understanding the distribution and drivers of microbial life in the sediment may give critical clues on how to search for biosignatures on Mars. Here, we identify the spatial distribution of highly specialized bacterial communities in previously unexplored depth horizons of subsurface sediments to a depth of 800 mm. We deployed an autonomous rover in a mission-relevant Martian drilling scenario with manual sample validation. Subsurface communities were delineated by depth related to sediment moisture. Geochemical analysis indicated soluble salts and minerology that influenced water bio-availability, particularly in deeper sediments. Colonization was also patchy and uncolonized sediment was associated with indicators of extreme osmotic challenge. The study identifies linkage between biocomplexity, moisture and geochemistry in Mars-like sediments at the limit of habitability and demonstrates feasibility of the rover-mounted drill for future Mars sample recovery.

Reaching 1 m deep on Mars: the Icebreaker drill

The future exploration of Mars will require access to the subsurface, along with acquisition of samples for scientific analysis and ground-truthing of water ice and mineral reserves for in situ resource utilization. The Icebreaker drill is an integral part of the Icebreaker mission concept to search for life in ice-rich regions on Mars. Since the mission targets Mars Special Regions as defined by the Committee on Space Research (COSPAR), the drill has to meet the appropriate cleanliness standards as requested by NASA's Planetary Protection Office. In addition, the Icebreaker mission carries life-detection instruments; and in turn, the drill and sample delivery system have to meet stringent contamination requirements to prevent false positives. This paper reports on the development and testing of the Icebreaker drill, a 1 m class rotary-percussive drill and triple redundant sample delivery system. The drill acquires subsurface samples in short, approximately 10 cm bites, which makes the sampling system robust and prevents thawing and phase changes in the target materials. Autonomous drilling, sample acquisition, and sample transfer have been successfully demonstrated in Mars analog environments in the Arctic and the Antarctic Dry Valleys, as well as in a Mars environmental chamber. In all environments, the drill has been shown to perform at the "1-1-100-100" level; that is, it drilled to 1 m depth in approximately 1 hour with less than 100 N weight on bit and approximately 100 W of power. The drilled substrate varied and included pure ice, ice-rich regolith with and without rocks and with and without 2% perchlorate, and whole rocks. The drill is currently at a Technology Readiness Level (TRL) of 5. The next-generation Icebreaker drill weighs 10 kg, which is representative of the flightlike model at TRL 5/6.

Dual release of proteins from porous polymeric scaffolds

To create porous scaffolds releasing in a controlled and independent fashion two different proteins, a novel approach based on protein-loaded polymeric coatings was evaluated. In this process, two water-in-oil emulsions are forced successively through a prefabricated scaffold to create coatings, containing each a different protein and having different release characteristics. In a first step, a simplified three-layered system was designed with model proteins (myoglobin and lysozyme). Poly(ether-ester) multiblock copolymers were chosen as polymer matrix, to allow the diffusion of proteins through the coatings. The model system showed the independent release of the two proteins. The myoglobin release was tailored from a burst to a linear release still on-going after 60 days, while the lysozyme release rate was kept constant. Macro-porous scaffolds, with a porosity of 59 vol.%, showed the same ability to control the release rate of the model proteins independently. The relation between the coatings properties and their release characteristics were investigated with the use of a mathematical diffusion model based on Fick's second law. It confirmed that the multiple coated scaffolds are biphasic system, where each coating controls the release of the protein that it contains. This approach could be of value for tissue engineering applications.

Pancam multispectral imaging results from the Spirit Rover at Gusev Crater

Panoramic Camera images at Gusev crater reveal a rock-strewn surface interspersed with high- to moderate-albedo fine-grained deposits occurring in part as drifts or in small circular swales or hollows. Optically thick coatings of fine-grained ferric iron-rich dust dominate most bright soil and rock surfaces. Spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near-infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine. Atmospheric observations show a steady decline in dust opacity during the mission, and astronomical observations captured solar transits by the martian moons, Phobos and Deimos, as well as a view of Earth from the martian surface.

Pancam multispectral imaging results from the Spirit Rover at Gusev Crater

Panoramic Camera images at Gusev crater reveal a rock-strewn surface interspersed with high- to moderate-albedo fine-grained deposits occurring in part as drifts or in small circular swales or hollows. Optically thick coatings of fine-grained ferric iron-rich dust dominate most bright soil and rock surfaces. Spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near-infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine. Atmospheric observations show a steady decline in dust opacity during the mission, and astronomical observations captured solar transits by the martian moons, Phobos and Deimos, as well as a view of Earth from the martian surface.