Biology subjects

Carr, C. E.

Publications and source records attributed to Carr, C. E..

At least 19 recordsLinked to original sources

bioRxiv2026

Anaerobic methane oxidation by ANME-2a at two molar chloride in Orca Basin

Anaerobic methane oxidation, typically mediated by consortia of archaea and bacteria, is a key process in the global methane cycle, but little is known about its upper salinity limits. We characterized the microbial methane cycle in the anoxic, hypersaline Orca Basin using metagenomics, metatranscriptomics, fluorescence in situ hybridization, and geochemical measurements at sub-meter resolution. In the brine, we detected transcriptional activity of the halophilic methylotrophic methanogen Methanohalophilus, consistent with a biological source for Orca Basin methane. In the particle-rich halocline ([~]2 M Cl-; [~]2235 meters depth), high mcrA transcription by a novel ANME-2a species was co-located with a positive shift in {delta}13C-CH4 indicative of anaerobic oxidation of methane. ANME-2a also transcribed genes for biosynthesis of the osmolyte N({varepsilon})-acetyl-{beta}-L-lysine, supporting adaptation for hypersaline conditions. At the same depth, consortia of sarcina-like archaea, likely ANME-2a, were observed in association with vibrioid and filamentous bacteria, potentially members of a halotolerant genus in the order Desulfobulbales (family SURF-16, which includes the previously identified ANME partner Seep-DBB) that were active at the same depth. At and above the oxic-anoxic interface, aerobic methane oxidation appears to be mediated by three genera of uncultivated Methylococcales bacteria. Our results double the upper salinity range of ANME-2a to [~]2 M Cl- and reveal the key microbial players in the methane bio-filter between the Orca Basin brine and overlying seawater.

microbiology↗

bioRxiv2025

Inhibitory inputs to avian ITD circuits

In birds, detection of sound source azimuth begins in the nucleus laminaris (NL), which computes interaural time differences (ITDs). Inhibition has been proposed to protect NL neurons from losing ITD sensitivity with increasing sound level, although the nature of this inhibition is incompletely understood. Anatomical studies show GABAergic synapses throughout NL and the first order nuclei, while in vitro studies in chicken NL showed that depolarizing, GABAergic inhibitory postsynaptic potentials (IPSPs) shorten membrane time constants, perhaps to allow the membrane potential to follow rapid synaptic currents accurately over a range of sound levels. Given the importance of inhibition in regulating auditory brainstem activity, we examined the nature of the inhibitory input to NL in vivo. The Superior Olivary Nucleus (SON) is the major source of descending GABAergic inhibition to the ipsilateral nucleus magnocellularis (NM), nucleus angularis (NA) and NL, and receives excitatory input from NA and NL. We used viral tracers to reveal projections from SON to NL, and characterized response types within SON. In NL, we isolated inhibitory synaptic contributions from extracellular field potentials through the iontophoretic application of blockers of GABA (gabazine) or glycine (strychnine). These blockers increase the onset and offset responses evoked by tonal stimuli, but did not shift best ITD. The co-application of gabazine and strychnine revealed supra-linear summation of GABA and glycine. Profiles of synaptic activation revealed more prominent inhibition following stimulus offset, suggesting inputs to NL originate from both the sustained and offset response types of the SON. These heterogeneous responses may represent separate SON neuronal populations.

neuroscience↗

bioRxiv2025

Predator type and relative risk affects the repeatability of nest defense in a songbird

Interindividual differences in nest defense towards a single predator type have been shown to be repeatable in multiple species, supporting the presence of personality. Here, we assessed if the nest defense of female northern house wrens (Troglodytes aedon) was repeatable across different types of predators, which is predicted by personality and largely untested. Over three years, we placed a decoy of a common nest predator, the eastern rat snake (Pantherophis alleghaniensis), on top of nest boxes and measured female behavior. Each season, we also presented a second stimulus of varying threat level, including an eastern chipmunk decoy (Tamias striatus), a taxidermied Coopers hawk (Accipiter cooperii), and a novel object of unknown threat. We measured repeatability between each pair of threats and compared the population-level response to the snake across years. Nest defense was significantly repeatable between the snake and chipmunk, which presented similar risks. It was also repeatable between the snake and novel object despite the population-level response to the object being significantly weaker. In contrast, nest defense was not repeatable between the snake and the hawk, which posed a significant threat to adult survival that may have disrupted the consistency of the female response. Finally, the average, population-level response to the snake did not detectably differ among years, indicating stability in this behavior despite high turnover in breeding adults. These results suggest the presence of personality in nest defense, but more research is needed to evaluate the effect of high-risk predators on the repeatability of this behavior. Significance StatementDifferences among individuals in the strength of nest defense are often repeatable towards a specific predator, indicating the presence of personality. However, few studies have tested the repeatability of nest defense across different predators of varying threat levels. Personality predicts that weak/strong responders to one predator should also be weak/strong to another. We tested this prediction in female northern house wrens by placing decoys of different predators and a novel object on top of their nest boxes to measure nest defense. Nest defense was repeatable between two predators of similar risk and between a predator and a novel object of unknown risk. However, nest defense was not repeatable between a low and high-risk predator. The results suggest the presence of personality, but research is needed on the effects of high-risk predators that appear to disrupt behavioral consistency.

animal behavior and cognition↗

bioRxiv2025

Validation of Gentamicin and Streptomycin Stability for On-Orbit Microbial Monitoring

The Genomic Enumeration of Antibiotic Resistance in Space (GEARS) flight project seeks to characterize the frequency and genomic identity of antibiotic-resistant organisms on the ISS and expand in-space sequencing-based diagnostic capabilities. This project selects for antibiotic-resistant microbes on space station surfaces using agar plates containing antibiotics, which can require storage of these plates for several months. However, little published data is available on the longevity of antibiotics in agar plates. Here, we describe the process of antibiotic selection and validation of antibiotic stability for GEARS. A literature review was conducted on several antibiotics for their intrinsic and acquired resistance in Enterococcus and Staphylococcus and stability in solution and in agar. Gentamicin and streptomycin were selected for a long-term study tracking changes in bactericidal ability of the antibiotics in agar plates. After 6.5 months of storage at 4{degrees}C, we found that both antibiotic types remained stable throughout the test period, although they both exhibited evidence of slight degradation. These findings indicated that either antibiotic would be sufficient for the GEARS study based on stability under cold stowage conditions. Furthermore, this study generated information on long-term stability of antibiotics in agar, which can be useful for microbiology applications beyond spaceflight studies.

microbiology↗

bioRxiv2024

Overcoming nucleotide bias in the nonenzymatic copying of RNA templates.

The RNA World hypothesis posits that RNA was the molecule of both heredity and function during the emergence of life. This hypothesis implies that RNA templates can be copied, and ultimately replicated, without the catalytic aid of evolved enzymes. A major problem with nonenzymatic templated polymerization has been the very poor copying of sequences containing rA and rU. Here we overcome that problem by using a prebiotically plausible mixture of RNA mononucleotides and random-sequence oligonucleotides, all activated by methyl isocyanide chemistry, that direct the uniform copying of arbitrary-sequence templates, including those harboring rA and rU. We further show that the use of this mixture in copying reactions suppresses copying errors while also generating a more uniform distribution of mismatches than observed for simpler systems. We find that oligonucleotide competition for template binding sites, oligonucleotide ligation, and the template binding properties of reactant intermediates work together to reduce product sequence bias and errors. Finally, we show that iterative cycling of the activation chemistry and templated polymerization improves the yield of random-sequence products. These results for random-sequence template copying are a significant advance in the pursuit of nonenzymatic RNA replication.

molecular biology↗

bioRxiv2024

Single neuron contributions to the auditory brainstem EEG

The auditory brainstem response (ABR) is an acoustically evoked EEG potential that is an important diagnostic tool for hearing loss, especially in newborns. The ABR originates from the response sequence of auditory nerve and brainstem nuclei, and a click-evoked ABR typically shows three positive peaks ( waves) within the first six milliseconds. However, an assignment of the waves of the ABR to specific sources is difficult, and a quantification of contributions to the ABR waves is not available. Here, we exploit the large size and physical separation of the barn owl first-order cochlear nucleus magnocellularis (NM) to estimate single-cell contributions to the ABR. We simultaneously recorded NM neurons spikes and the EEG in owls of both sexes, and found that {gtrsim} 5, 000 spontaneous single-cell spikes are necessary to isolate a significant spike-triggered average response at the EEG electrode. An average single-neuron contribution to the ABR was predicted by convolving the spike-triggered average with the cells peri-stimulus time histogram. Amplitudes of predicted contributions of single NM cells typically reached 32.9 {+/-} 1.1 nV (mean {+/-} SE, range: 2.5 - 162.7 nV), or 0.07 {+/-} 0.02% (median {+/-} SE; range from 0.01% to 1%) of the ABR amplitude. The time of the predicted peak coincided best with the peak of the ABR wave II, independent of the click sound level. Our results suggest that individual neurons contributions to an EEG can vary widely, and that wave II of the ABR is shaped by NM units. Significance statementThe auditory brainstem response (ABR) is a scalp potential used for the diagnosis of hearing loss, both clinically and in research. We investigated the contribution of single action potentials from auditory brainstem neurons to the ABR and provide direct evidence that action potentials recorded in a first order auditory nucleus, and their EEG contribution, coincide with wave II of the ABR. The study also shows that the contribution of single cells varies strongly across the population.

neuroscience↗

bioRxiv2024

Nanogap Solid-State Single-Molecule Detection at Mars, Europa, and Microgravity Conditions

Solid-state nanogap systems are an emerging technology for in-situ life detection due to their single-molecule resolution of a wide range of biomolecules, including amino acids and informational polymers, at the parts per billion to trillion level. By targeting the abundance distributions of organic molecules, this technology is a candidate for detecting ancient and extant life and discriminating between biotic and abiotic organics on future planetary missions to Mars and icy moons such as Enceladus and Europa. A benchtop system developed at Osaka University has a proven ability to detect and discriminate among single amino acids, RNA, and DNA using nanogap chips. The Electronic Life-detection Instrument for Enceladus/Europa (ELIE) prototype was subsequently developed to make this technology viable for space instrumentation through the simplification of electronics, reduction of size and weight, and automation of gap formation. Initial ground testing using a manually formed nanogap with the first ELIE prototype detected the amino acid L-proline. However, this manual adjustment approach posed limitations in maintaining a consistent gap size. To address this challenge, we integrated an automated piezo actuator to enable real-time gap control, permitting single-molecule identification of a target amino acid, L-proline, under reduced gravity (g), including Mars (g = 0.378), Europa or Lunar (g = 0.166), and microgravity conditions (g = 0.03-0.06), as validated through parabolic flight testing. Power supply noise and experimental constraints of the experiment design limited data collection to short segments of good-quality data. Nevertheless, the subsequent analysis of detected events within these segments revealed a consistent system performance and a controlled gap size across the different accelerations. This finding highlights the systems resilience to physical vibrations. Future goals are to progress the instrument towards technology readiness level 4 with further reductions of size and mass, lower noise, and additional system automation. With further development, ELIE has the potential to be an autonomous and sensitive single-molecule detection instrument for deployment throughout the solar system.

biophysics↗

bioRxiv2023

Translation as a Biosignature

Life on Earth relies on mechanisms to store heritable information and translate this information into cellular machinery required for biological activity. In all known life, storage, regulation, and translation are provided by DNA, RNA, and ribosomes. Life beyond Earth, even if ancestrally or chemically distinct from life as we know it may utilize similar structures: it has been proposed that charged linear polymers analogous to nucleic acids may be responsible for storage and regulation of genetic information in non-terran biochemical systems. We further propose that a ribosome-like structure may also exist in such a system, due to the evolutionary advantages of separating heritability from cellular machinery. Here, we use a solid-state nanopore to detect DNA, RNA, and ribosomes, and demonstrate that machine learning can distinguish between biomolecule samples and accurately classify new data. This work is intended to serve as a proof of principal that such biosignatures (i.e., informational polymers or translation apparatuses) could be detected, for example, as part of future missions targeting extant life on Ocean Worlds. A negative detection does not imply the absence of life; however, detection of ribosome-like structures could provide a robust and sensitive method to seek extant life in combination with other methods. One Sentence SummaryLife, defined as a chemical system capable of Darwinian evolution, likely requires an apparatus to translate heritable instructions into cellular machinery, and we propose to detect this as a biosignature of extant life beyond Earth.

biophysics↗

bioRxiv2023

Experience-Dependent Plasticity in Nucleus Laminaris of the Barn Owl

Barn owls experience increasing interaural time differences (ITDs) during development, because their head width more than doubles in the month after hatching. We therefore hypothesized that their ITD detection circuit might be modified by experience. To test this, we raised owls with unilateral ear inserts that delayed and attenuated the acoustic signal, then measured the ITD representation in the brainstem nucleus laminaris (NL) when they were adult. The ITD circuit is composed of delay line inputs to coincidence detectors, and we predicted that plastic changes would lead to shorter delays in the axons from the manipulated ear, and complementary shifts in ITD representation on the two sides. In owls that received ear inserts starting around P14, the maps of ITD shifted in the predicted direction, but only on the ipsilateral side, and only in those tonotopic regions that had not experienced auditory stimulation prior to insertion. The contralateral map did not change. Experience-dependent plasticity of the ITD circuit occurs in NL, and our data suggest that ipsilateral and contralateral delays are independently regulated. Thus, altered auditory input during development leads to long-lasting changes in the representation of ITD. Significance StatementThe early life of barn owls is marked by increasing sensitivity to sound, and by increasing ITDs. Their prolonged post-hatch development allowed us to examine the role of altered auditory experience on the development of ITD detection circuits. We raised owls with a unilateral ear insert and found that their maps of ITD were altered by experience, but only in those tonotopic regions that had not experienced auditory stimulation prior to insertion. Thus experience-induced plasticity allows the sound localization circuits to be customized to individual characteristics, such as the size of the head, and potentially to compensate for natural conductive hearing losses.

neuroscience↗

bioRxiv2022

Solid-State Single-Molecule Sensing with the Electronic Life-detection Instrument for Enceladus/Europa (ELIE)

Growing evidence of the potential habitability of Ocean Worlds across our Solar System is motivating the advancement of technologies capable of detecting life as we know it - sharing a common ancestry or common physicochemical origin to life on Earth - or dont know it, representing a distinct genesis event of life quite different than our one known example. Here, we propose the Electronic Life-detection Instrument for Enceladus/Europa (ELIE), a solid-state single-molecule instrument payload that aims to search for life based on the detection of amino acids and informational polymers (IPs) at the parts per billion to trillion level. As a first proof-of- principle in a laboratory environment, we demonstrate single-molecule detection of the amino acid L-proline at a 10 {micro}M concentration in a compact system. Based on ELIEs solid-state quantum electronic tunneling sensing mechanism, we further propose the quantum property of the HOMO-LUMO gap (energy difference between a molecules highest energy occupied molecular orbital and lowest energy unoccupied molecular orbital) as a novel approach to measure amino acid complexity. Finally, we assess the potential of ELIE to discriminate between abiotically and biotically derived (-amino acids in order to reduce false positive risk for life detection. Nanogap technology can also be applied to the detection of nucleobases and short sequences of IPs such as, but not limited to, RNA and DNA. Future missions may utilize ELIE to target preserved biosignatures on the surface of Mars, extant life in its deep subsurface, or life or its biosignatures in the plume, surface, or subsurface of ice moons such as Enceladus or Europa. One Sentence SummaryA solid-state nanogap can determine the abundance distribution of amino acids, detect nucleic acids, and shows potential for detecting life as we know it and life as we dont.

biophysics↗

bioRxiv2022

A general mechanism of air-borne hearing in Recent and early non-tympanate tetrapods

Tetrapod tympanic hearing probably emerged in the Triassic with independent origins in each of the major groups, more than 120 Myr after the water-land transition. During this long period, any auditory sensitivity must have been based on non-tympanic, bone conduction mechanisms. However, bone conduction is a non-specific term describing several different modes of vibration that can stimulate the inner ear. To understand hearing in a non-tympanic ear, we focus on the simplest model: that sound translates the head, i.e., that the head is pushed and pulled by the sound wave, and that this vibration is transduced by the inner ear. Simple translation is the mode of human low-frequency bone conduction sensitivity and translation by underwater sound is also the mode of auditory stimulation for most fishes. It is therefore a straightforward assumption that this may have been the mechanism of hearing in the early tetrapods. According to acoustic theory, the efficiency of translation of an object by sound is determined by its density and ka, the product of the acoustic wavenumber (k) and the radius (a) of the head. Simple finite-element models of translation by sound show that vibration velocities only depend on ka and density (for objects of the same shape and composition) and are almost constant (between 4 and 5 {micro}m/s/Pa depending on shape) for objects with ka<1. We compare sensitivity to sound and to vibrations of the skull in animals lacking tympanic middle ears (snakes, salamanders, earless frogs, and lungfish) and show that the low-frequency air-borne sound sensitivity in these species is largely consistent with a translation mechanism. How translation of the head or body can stimulate the inner ear is most evident in an inertial system like the otolithic/otoconial ears of fish and early tetrapods, but fluid inertia in the inner ear may also generate hydrodynamic waves that can stimulate hair cells in the tetrapod inner ear, providing a mechanism for this simple mode of sound reception to confer hearing in earless animals.

animal behavior and cognition↗

bioRxiv2021

Microbial habitability of the early Mars lacustrine environment sustained by iron redox cycling

Several studies have reported new data on the estimated compositions of chemical components at Gale crater; however, there is still a lack of information regarding potential past support of biomass and detectable biomarkers of ancient life. In this study we evaluate microbial habitability of early Mars constrained by the recently reconstructed water chemistry at Gale. The modeled community is based on Fe-metabolizing bacteria with the ability to utilize solid-phase iron oxides (e.g., magnetite) as an electron source or sink. Our results illustrate the plausibility of a sustained community in Gale Lake and provides suggestions for future modelled and laboratory-based studies to further evaluate the past habitability of Mars, biosignatures and their preservation potential, and hidden metabolic potential. One Sentence SummaryThis work provides an existence proof of habitability on early Mars and demonstrates modeling processes by which the habitability of extraterrestrial environments can be explored quantitatively.

microbiology↗

bioRxiv2021

Freeze-thaw Cycles Enable a Prebiotically Plausible and Continuous Pathway from Nucleotide Activation to Nonenzymatic RNA Copying

Nonenzymatic template-directed RNA copying using chemically activated nucleotides is thought to have played a key role in the emergence of genetic information on the early Earth. A longstanding question concerns the number and nature of different environments that might have been necessary to enable all of the steps from nucleotide synthesis to RNA replication. Here we explore three sequential steps from this overall pathway: nucleotide activation, synthesis of imidazolium-bridged dinucleotides, and template-directed primer extension. We find that all three steps can take place in one reaction mixture, under conditions of multiple freeze-thaw cycles. Recent experiments have demonstrated a potentially prebiotic methyl isocyanide-based nucleotide activation chemistry. Unfortunately, the original version of this approach is incompatible with nonenzymatic RNA copying because the high required concentration of the imidazole activating group prevents the accumulation of the essential imidazolium-bridged dinucleotide needed for primer extension. Here we report that ice eutectic phase conditions facilitate not only the methyl isocyanide-based activation of ribonucleotide 5'-monophosphates with stoichiometric 2-aminoimidazole, but also the subsequent conversion of these activated mononucleotides into imidazolium-bridged dinucleotides. Furthermore, this one pot approach is compatible with template-directed primer extension in the same reaction mixture. Our results suggest that the simple and common environmental fluctuation of freeze-thaw cycles could have played an important role in prebiotic nucleotide activation and nonenzymatic RNA copying. Significance StatementThe replication of RNA without the aid of evolved enzymes may have enabled the inheritance of useful molecular functions during the origin of life. Several key steps on the path to RNA replication have been studied in isolation, including chemical nucleotide activation, synthesis of a key reactive intermediate, and nonenzymatic RNA copying. Here we report a prebiotically plausible scenario under which these reactions can happen together under mutually compatible conditions. Thus, this pathway could potentially have operated in nature without the complicating requirement for exchange of materials between distinct environments.

biochemistry↗

bioRxiv2021

Competition between bridged dinucleotides and activated mononucleotides determines the error frequency of nonenzymatic RNA primer extension

Nonenzymatic copying of RNA templates with activated nucleotides is a useful model for studying the emergence of heredity at the origin of life. Previous experiments with defined-sequence templates have pointed to the poor fidelity of primer extension as a major problem. Here we examine the origin of mismatches during primer extension on random templates in the simultaneous presence of all four 2-aminoimidazole-activated nucleotides. Using a deep sequencing approach that reports on millions of individual template-product pairs, we are able to examine correct and incorrect polymerization as a function of sequence context. We have previously shown that the predominant pathway for primer extension involves reaction with imidazolium-bridged dinucleotides, which form spontaneously by the reaction of two mononucleotides with each other. We now show that the sequences of correctly paired products reveal patterns that are expected from the bridged dinucleotide mechanism, whereas those associated with mismatches are consistent with direct reaction of the primer with activated mononucleotides. Increasing the ratio of bridged dinucleotides to activated mononucleotides, either by using purified components or by using isocyanide-based activation chemistry, reduces the error frequency. Our results point to testable strategies for the accurate nonenzymatic copying of arbitrary RNA sequences.

molecular biology↗

bioRxiv2020

Deep sequencing of nonenzymatic RNA primer extension

Life emerging in an RNA world is expected to propagate RNA as hereditary information, requiring some form of primitive replication without enzymes. Nonenzymatic template-directed RNA primer extension is a model of the polymerisation step in this posited form of replication. The sequence space accessed by primer extension dictates potential pathways to self-replication and, eventually, ribozymes. Which sequences can be accessed? What is the fidelity of the reaction? Does the recently-illuminated mechanism of primer extension affect the distribution of sequences that can be copied? How do sequence features respond to experimental conditions and prebiotically relevant contexts? To help answer these and related questions, we here introduce a deep-sequencing methodology for studying RNA primer extension. We have designed and vetted special RNA constructs for this purpose, honed a protocol for sample preparation and developed custom software that sorts and analyses raw sequencing data. We apply this new methodology to proof-of-concept controls, and demonstrate that it works as expected and reports on key features of the sequences accessed by primer extension.

synthetic biology↗

bioRxiv2020

Nanopore Sequencing at Mars, Europa and Microgravity Conditions

Nanopore sequencing, as represented by Oxford Nanopore Technologies MinION, is a promising technology for in situ life detection and for microbial monitoring including in support of human space exploration, due to its small size, low mass ([~]100 g) and low power ([~]1W). Now ubiquitous on Earth and previously demonstrated on the International Space Station (ISS), nanopore sequencing involves translocation of DNA through a biological nanopore on timescales of milliseconds per base. Nanopore sequencing is now being done in both controlled lab settings as well as in diverse environments that include ground, air and space vehicles. Future space missions may also utilize nanopore sequencing in reduced gravity environments, such as in the search for life on Mars (Earth-relative gravito-inertial acceleration (GIA) g = 0.378), or at icy moons such as Europa (g = 0.134) or Enceladus (g = 0.012). We confirm the ability to sequence at Mars as well as near Europa or Lunar (g = 0.166) and lower g levels, demonstrate the functionality of updated chemistry and sequencing protocols under parabolic flight, and reveal consistent performance across g level, during dynamic accelerations, and despite vibrations with significant power at translocation-relevant frequencies. Our work strengthens the use case for nanopore sequencing in dynamic environments on Earth and in space, including as part of the search for nucleic-acid based life beyond Earth.

genomics↗

bioRxiv2019

A First-Order Design Requirement to Prevent Edema in Mechanical Counter-Pressure Space Suit Garments

IntroductionMechanical counter-pressure (MCP) space suits may provide enhanced mobility relative to gas-pressure space suits. One challenge to realizing operational MCP suits is the potential for edema caused by spatial variations in the applied body-surface pressure (dP). We determined a first-order requirement for these variations.\n\nMethodsDarcys law relates volume flux, of fluid from capillaries to the interstitial space, to transmural hydraulic and osmotic pressure differences. Albumin and fibrinogen levels determine, to first order, the capillary oncotic pressure (COP). We estimated dP, neglecting hydrostatic pressure differences, by equating the volume flux under MCP and under normal with the volume flux under abnormal variations in COP; then we compared these estimates to results from MCP garment studies.\n\nResultsNormal COP varies from 20-32 mm Hg; with constant hydraulic conductivity, dP{approx}12 mm Hg. In nephrotic syndrome, COP may drop to 11 mm Hg, yielding dP{approx}15 mm Hg relative to mid-normal COP. Previous studies found dPmax =151 mm Hg (MCP glove; finger and hand dorsum relative to palm), dPmax=51 mm Hg (MCP arm; finger, hand dorsum, and wrist relative to arm), and dP=52, 90 and 239 mm Hg (three MCP lower leg garments).\n\nConclusionsMCP garments with dPmax[≤]12 mm Hg are unlikely to produce edema or restrict capillary blood flow; however, garments with dPmax>12 mm Hg will not necessarily produce edema. For example, the hydrostatic pressure gradient at the feet in 1g can range from 70-90 mm Hg. Current garment prototypes do not meet our conservative design requirement.

physiology↗

bioRxiv2018

Nucleic acid extraction and sequencing from low-biomass synthetic Mars analog soils for in situ life detection

Recent studies regarding the origin of life and Mars-Earth meteorite transfer simulations suggest that biological informational polymers, such as nucleic acids (DNA and RNA), have the potential to provide unambiguous evidence of life on Mars. To this end, we are developing a metagenomics-based life-detection instrument which integrates nucleic acid extraction and nanopore sequencing: The Search for Extra-Terrestrial Genomes (SETG). Our goal is to isolate and sequence nucleic acids from extant or preserved life on Mars in order to determine if a particular genetic sequence (1) is distantly-related to life on Earth indicating a shared-ancestry due to lithological exchange, or (2) is unrelated to life on Earth suggesting a convergent origin of life on Mars. In this study, we validate prior work on nucleic acid extraction from cells deposited in Mars analog soils down to microbial concentrations observed in the driest and coldest regions on Earth. In addition, we report low-input nanopore sequencing results equivalent to 1 ppb life-detection sensitivity achieved by employing carrier sequencing, a method of sequencing sub-nanogram DNA in the background of a genomic carrier.

molecular biology↗