Plasma instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks may be responsible for particle (electron, positron, and ion) acceleration. Using a ...three-dimensional relativistic electromagnetic particle code, we have investigated long-term particle acceleration associated with relativistic electron-ion or electron-positron jet fronts propagating into an unmagnetized ambient electron-ion or electron-positron plasma. These simulations have been performed with a longer simulation system than our previous simulations in order to investigate the nonlinear stage of the Weibel instability and its particle acceleration mechanism. The current channels generated by the Weibel instability are surrounded by toroidal magnetic fields and radial electric fields. This radial electric field is quasi stationary and accelerates particles that are then deflected by the magnetic field. Whether particles are accelerated or decelerated along the jet propagation direction depends on the velocity of particles and the sign of super(E) X super(B) in the moving frame of each particle. For the electron-ion case the large-scale current channels generated by the ion Weibel instability lead to more acceleration near the jet head. Consequently, the accelerated jet electrons in the electron-ion jet have a significant hump above a thermal distribution. However, in the electron-positron case, accelerated jet electrons have a smoother, nearly thermal distribution. In the electron-positron case, initial acceleration occurs as current channels form and then continues at a much lesser rate as the current channels and corresponding toroidal magnetic fields generated by the Weibel instability dissipate.
Lava tubes are key targets in the search for life on Mars. Their basaltic walls provide protection from radiation and changing environmental conditions, which could enable life or preservation of ...previous life in an otherwise harsh environment. We can understand the potential for Martian life in lava tubes by studying the habitability of analog environments on Earth. In this study, we present the first characterization of the microbial life inside a pristine Mauna Loa lava tube. This study is the first to combine 16S SSU rRNA sequencing and whole genome shotgun sequencing to map the taxonomic makeup and functional potential of any lava tube community in Hawaii, enabling a deep understanding of the types of microbes that thrive in this unique environment and the metabolisms they use. We find a surprisingly high degree of niche partitioning over small spatial scales and discuss implications for life detection strategies. Based on recent bioinformatic advancements in metagenomics, we also assemble dozens of high‐quality metagenome assembled genomes from the microbes living in the lava tubes, including several novel species.
Plain Language Summary
In the search for life on Mars, lava tubes are targets for astrobiology. Lava tubes provide an underground shelter, protected from radiation and the harsh climate. Analog studies here on Earth can help us understand what types of microbes live in these terrains and how best to find them. In this study, we investigate the microbial communities in a previously unexplored lava tube on the Mauna Loa volcano in Hawaii. We set out to characterize the microbes that live there and what capabilities enable them to survive, such as how they acquire nutrients from their environment to produce energy. We collected mineral samples in the lava tube and sequenced the DNA that we found in the minerals. We used DNA sequences to identify which microbes are present as well as which metabolisms they can use. We found that there are significant differences in the microbial make‐up of each of the samples, even though some are taken within several centimeters of each other, with implications for how to assay a region of interest on Mars. We also found several novel species.
Key Points
In this undisturbed environment, communities were characterized by multiple microniches, varying widely over the scale of meters
The lava tube contained high amounts of “microbial dark matter” or uncultivated microbes that remain unclassified in taxonomic databases
Although the mineralogy of many of the samples we studied was sulfate‐rich, metabolisms unrelated to sulfur dominated the metagenome
Here, we present the draft genome for a new putative species, Gaiellasilicea maunaloa, most closely related to Gaiella occulta, within the phylum Actinobacteria. This group contains Gram-negative, ...aerobic mesophilic species. This metagenome-assembled genome (MAG) contributes to knowledge of life in volcanic environments and may inform investigations of life beyond Earth.
We report the draft genome sequence of a putative new genus and species, Siliceabacter maunaloa, in the family Solirubrobacteraceae. The members of this family of Actinobacteria are generally Gram ...positive and mesophilic. Found within a Hawaiian lava tube, this microbe illuminates the types of prokaryotes inhabiting secondary minerals in subsurface basaltic environments.
Life detection in the solar system relies on the unambiguous identification of signatures of life and habitability. Organic molecules are essential to life as we know it, and yet many organic ...compounds are ubiquitous in the solar system and can be synthesized abiotically; thus, their presence alone is not indicative of life. On Earth, chemical signatures of life's processes are often left behind in minerals through the biologically induced formation of secondary minerals or intermediary organic complexes. In natural rocks biomolecules and organic species often co-occur with minerals, and their overlapping peaks can create difficulties in interpretation. In the process of identifying the minerals and organic species in our basaltic samples we noticed signatures for cyanates co-occurring with organic molecules. Cyanates are an overlooked group of nitrogen compounds in which C is bonded to N (e.g., OCN− or SCN−) that often co-occur with urea and ammonium in environments where microorganisms are present. These compounds are common in many terrestrial and oceanic environments and play an important role in biogeochemical nitrogen cycling. In natural systems, these compounds form as the result of multiple biogeochemical pathways, often from the interaction of microbes with a chemically active environment. These interactions leave behind signatures in the form biotic breakdown products such as urea or ammonium and organic reaction byproducts that are observable with spectroscopic methods. To explore these relationships, we used field-portable Raman spectrometers and laboratory micro-Raman imaging to characterize and compare samples collected from two different terrestrial basaltic environments, a lava tube on Mauna Loa, Hawaii, dominated by the precipitation of sulfate minerals and a geothermal stream at Hveragil, Iceland dominated by the precipitation of carbonate minerals. The Raman (RS) measurements were complemented by laser induced breakdown spectroscopy (LIBS), Long-wave Infrared (IR) LIBS, with the addition of gas chromatograph mass spectrometry (GC–MS) and inductively coupled plasma-mass spectrometry (ICP-MS) to identify cyanate compounds, biomolecules, and other nitrogenous compounds related to the breakdown or production of cyanate in host basalts and secondary precipitates. The RS data suggest that the reason for RS cyanate signatures in the carbonate samples could be due to luminescence artifacts while those detected in the host basalts may be due to hydrolysis chemistry. The cyanate signatures detected in the lava tube samples dominated by sulfates do not seem to be luminescence artifacts but may in fact be evidence of an active microbial nitrogen cycle. Our results inform the spectroscopic detection of cyanates in planetary analog environments and the challenges in their identification. Further work is needed to understand their potential as biosignatures on other planetary bodies.
•Basaltic environs have detectable features useful to search for life beyond Earth.•N-compounds (cyanates) are observed with secondary minerals and organic molecules.•Raman spectroscopy, LIBS, GC–MS, ICP-MS are complementary for life detection.
The objective of this study was to determine the disposition of ampicillin in plasma, uterine tissue, lochial fluid, and milk of postpartum dairy cattle. Ampicillin trihydrate was administered by ...intramuscular (i.m.) injection at a dose of 11 mg/kg of body weight every 24 h (n = 6, total of 3 doses) or every 12 h (n = 6, total of 5 doses) for 3 days. Concentrations of ampicillin were measured in plasma, uterine tissue, lochial fluid, and milk using HPLC with ultraviolet absorption. Quantifiable ampicillin concentrations were found in plasma, milk, and lochial fluid of all cattle within 30 min, 4 h, and 4 h of administration of ampicillin trihydrate, respectively. There was no significant effect of dosing interval (every 12 vs. every 24 h) and no significant interactions between dosing interval and sampling site on the pharmacokinetic variable measured or calculated. Median peak ampicillin concentration at steady‐state was significantly higher in lochial fluid (5.27 μg/mL after q 24 h dosing) than other body fluids or tissues and significantly higher in plasma (3.11 μg/mL) compared to milk (0.49 μg/mL) or endometrial tissue (1.55 μg/mL). Ampicillin trihydrate administered once daily by the i.m. route at the label dose of 11 mg/kg of body weight achieves therapeutic concentrations in the milk, lochial fluid, and endometrial tissue of healthy postpartum dairy cattle.
The effects of task importance and group decision training on the discussion behavior of decision-making groups were investigated. Three-person groups decided which of 3 hypothetical faculty ...candidates would be the best person to teach an introductory psychology course. Prior to discussion, some of the information about each candidate was given to all group members (shared information), whereas the remainder was randomly divided among them (unshared information). In general, groups discussed much more of their shared information than their unshared information. Increasing the importance of the task slowed the rate at which information was brought forth during discussion. By contrast, group decision training increased the amount of both shared and unshared information discussed and altered the sequential flow of shared and unshared information into the discussion: Discussion in untrained groups focused first on shared information and then on unshared information; discussion in trained groups did not shift focus over time. Results are discussed in terms of an information-sampling model of group discussion and the role of discussion in group decision-making effectiveness.
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