Biological system development for GraviSat: A new platform for studying photosynthesis and microalgae in space

Microalgae have great potential to be used as part of a regenerative life support system and to facilitate in-situ resource utilization (ISRU) on long-duration human space missions. Little is currently known, however, about microalgal responses to the space environment over long (months) or even short (hours to days) time scales. We describe here the development of biological support subsystems for a prototype “3U” (i.e., three conjoined 10-cm cubes) nanosatellite, called GraviSat, designed to experimentally elucidate the effects of space microgravity and the radiation environment on microalgae and other microorganisms. The GraviSat project comprises the co-development of biological handling-and-support technologies with implementation of integrated measurement hardware for photosynthetic efficiency and physiological activity in support of long-duration (3–12 months) space missions. It supports sample replication in a fully autonomous system that will grow and analyze microalgal cultures in 120μL wells around the circumference of a microfluidic polymer disc; the cultures will be launched while in stasis, then grown in orbit. The disc spins at different rotational velocities to generate a range of artificial gravity levels in space, from microgravity to multiples of Earth gravity. Development of the biological support technologies for GraviSat comprised the screening of more than twenty microalgal strains for various physical, metabolic and biochemical attributes that support prolonged growth in a microfluidic disc, as well as the capacity for reversible metabolic stasis. Hardware development included that necessary to facilitate accurate and precise measurements of physical parameters by optical methods (pulse amplitude modulated fluorometry) and electrochemical sensors (ion-sensitive microelectrodes). Nearly all microalgal strains were biocompatible with nanosatellite materials; however, microalgal growth was rapidly inhibited (~1 week) within sealed microwells that did not include dissolved bicarbonate due to CO2 starvation. Additionally, oxygen production by some microalgae resulted in bubble formation within the wells, which interfered with sensor measurements. Our research achieved prolonged growth periods (\u3e10months) without excess oxygen production using two microalgal strains, Chlorella vulgaris UTEX 29 and Dunaliella bardawil 30.861, by lowering light intensities (2–10μmol photons m−2s−1) and temperature (4–12˚C). Although the experiments described here were performed to develop the GraviSat platform, the results of this study should be useful for the incorporation of microalgae in other satellite payloads with low-volume microfluidic systems

Unexpected diversity and complexity of the Guerrero Negro hypersaline microbial mat

Author Posting. © The Author(s), 2006. This is the author's version of the work. It is posted here by permission of American Society for Microbiology for personal use, not for redistribution. The definitive version was published in Applied and Environmental Microbiology 72 (2006): 3685-3695, doi:10.1128/AEM.72.5.3685-3695.2006.We applied nucleic acids-based molecular methods, combined with estimates of biomass (ATP), pigments and microelectrode measurements of chemical gradients, to map microbial diversity vertically on the mm-scale in a hypersaline microbial mat from Guerrero Negro, Baja California Sur, Mexico. To identify the constituents of the mat, small-subunit ribosomal RNA genes were amplified by PCR from community genomic DNA extracted from layers, cloned and sequenced. Bacteria dominated the mat and displayed unexpected and unprecedented diversity. The majority (1336) of 1586 bacterial 16S rRNA sequences generated were unique, representing 752 species (≥97% rRNA sequence identity) in 42 of the main bacterial phyla, including 15 novel candidate phyla. The diversity of the mat samples differentiated according to the chemical milieu defined by concentrations of O2 and H2S. Chloroflexi formed the majority of the biomass by percentage of bulk rRNA and of clones in rRNA gene libraries. This result contradicts the general belief that Cyanobacteria dominate these communities. Although Cyanobacteria constituted a large fraction of the biomass in the upper few mm (>80% of total rRNA and photosynthetic pigments), Chloroflexi sequences were conspicuous throughout the mat. Filamentous Chloroflexi were identified by fluorescent in-situ hybridization within the polysaccharide sheaths of the prominent cyanobacterium Microcoleus chthonoplastes in addition to free-living in the mat. The biological complexity of the mat far exceeds that observed in other polysaccharide-rich microbial ecosystems, such as human and mouse distal guts, and suggests that positive feedbacks exist between chemical complexity and biological diversity.R. Ley was supported in part by an NRC- NASA Astrobiology Institutes Post Doctoral Associateship, J. Spear by an Agouron Institute postdoctoral fellowship. This work was supported by the NASA Cooperative Agreement with the University of Colorado Center for Astrobiology to N. R. Pace

Carbonate-Templated Self-Assembly of an Alkylthiolate-Bridged Cadmium Macrocycle

In the presence of Cd(ClO4)2 and a base, a new mixed N,S-donor alkylthiolate ligand supported both carbonate formation from atmospheric CO2 and the self-assembly of a novel bicapped puckered (CdS)6 molecular wheel. The remarkable stability of the complex was demonstrated by slow intermolecular ligand exchange on the 2J(HH) and J(111/113Cd1H) time scales at elevated temperature. Both CO2 and the base were required to convert amorphous “CdLClO4” precipitated in the absence of air to the carbonate complex. The complex shares structural features with the ζ-carbonic anhydrase class associating cadmium(II) with the biogeochemical cycling of carbon and is the first structurally characterized carbonate complex of any metal involving an alkylthiolate ligand

Millimeter-scale genetic gradients and community-level molecular convergence in a hypersaline microbial mat

To investigate the extent of genetic stratification in structured microbial communities, we compared the metagenomes of 10 successive layers of a phylogenetically complex hypersaline mat from Guerrero Negro, Mexico. We found pronounced millimeter-scale genetic gradients that were consistent with the physicochemical profile of the mat. Despite these gradients, all layers displayed near-identical and acid-shifted isoelectric point profiles due to a molecular convergence of amino-acid usage, indicating that hypersalinity enforces an overriding selective pressure on the mat community

Atmospheric Evolution

Earth's atmosphere has evolved as volatile species cycle between the atmosphere, ocean, biomass and the solid Earth. The geochemical, biological and astrophysical processes that control atmospheric evolution are reviewed from an "Earth Systems" perspective, with a view not only to understanding the history of Earth, but also to generalizing to other solar system planets and exoplanets.Comment: 34 pages, 3 figures, 2 tables. Accepted as a chapter in "Encyclopaedia of Geochemistry", Editor Bill White, Springer-Nature, 201

Arc magmas sourced from melange diapirs in subduction zones

Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Nature Publishing Group for personal use, not for redistribution. The definitive version was published in Nature Geoscience 5 (2012): 862-867, doi:10.1038/ngeo1634.At subduction zones, crustal material is recycled back into the mantle. A certain proportion, however, is returned to the overriding plate via magmatism. The magmas show a characteristic range of compositions that have been explained by three-component mixing in their source regions: hydrous fluids derived from subducted altered oceanic crust and components derived from the thin sedimentary veneer are added to the depleted peridotite in the mantle beneath the volcanoes. However, currently no uniformly accepted model exists for the physical mechanism that mixes the three components and transports them from the slab to the magma source. Here we present an integrated physico-chemical model of subduction zones that emerges from a review of the combined findings of petrology, modelling, geophysics, and geochemistry: Intensely mixed metamorphic rock formations, so-called mélanges, form along the slab-mantle interface and comprise the characteristic trace-element patterns of subduction-zone magmatic rocks. We consider mélange formation the physical mixing process that is responsible for the geochemical three-component pattern of the magmas. Blobs of low-density mélange material, so-called diapirs, rise buoyantly from the surface of the subducting slab and provide a means of transport for well-mixed materials into the mantle beneath the volcanoes, where they produce melt. Our model provides a consistent framework for the interpretation of geophysical, petrological and geochemical data of subduction zones.H.M. was funded by the J. LamarWorzel Assistant Scientist Fund and the Penzance Endowed Fund in Support of Assistant Scientists. Funding from NSF grant #1119403 (G. Harlow) is acknowledged.2013-05-1

Onset of the aerobic nitrogen cycle during the Great Oxidation Event

The rise of oxygen on the early Earth (about 2.4 billion years ago)1 caused a reorganization of marine nutrient cycles2, 3, including that of nitrogen, which is important for controlling global primary productivity. However, current geochemical records4 lack the temporal resolution to address the nature and timing of the biogeochemical response to oxygenation directly. Here we couple records of ocean redox chemistry with nitrogen isotope (15N/14N) values from approximately 2.31-billion-year-old shales5 of the Rooihoogte and Timeball Hill formations in South Africa, deposited during the early stages of the first rise in atmospheric oxygen on the Earth (the Great Oxidation Event)6. Our data fill a gap of about 400 million years in the temporal 15N/14N record4 and provide evidence for the emergence of a pervasive aerobic marine nitrogen cycle. The interpretation of our nitrogen isotope data in the context of iron speciation and carbon isotope data suggests biogeochemical cycling across a dynamic redox boundary, with primary productivity fuelled by chemoautotrophic production and a nitrogen cycle dominated by nitrogen loss processes using newly available marine oxidants. This chemostratigraphic trend constrains the onset of widespread nitrate availability associated with ocean oxygenation. The rise of marine nitrate could have allowed for the rapid diversification and proliferation of nitrate-using cyanobacteria and, potentially, eukaryotic phytoplankton

Seismic evidence for fluids in fault zones on top of the subducting Cocos Plate beneath Costa Rica

Author Posting. © The Authors, 2010. This article is posted here by permission of John Wiley & Sons for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 181 (2010): 997-1016, doi:10.1111/j.1365-246X.2010.04552.x.In the 2005 TICOCAVA explosion seismology study in Costa Rica we observed crustal turning waves with a dominant frequency of ~10 Hz on a linear array of short-period seismometers from the Pacific Ocean to the Caribbean Sea. On one of the shot records, from Shot 21 in the backarc of the Cordillera Central, we also observed two seismic phases with an unusually high dominant frequency (~20 Hz). These two phases were recorded in the forearc region of central Costa Rica and arrived ~7 s apart and 30 to 40 s after the detonation of Shot 21. We considered the possibility that these secondary arrivals were produced by a local earthquake that may have happened during the active-source seismic experiment. Such high-frequency phases following Shot 21 were not recorded after Shots 22, 23, and 24, all in the backarc of Costa Rica, which might suggest that they were produced by some other source. However, earthquake dislocation models cannot produce seismic waves of such high frequency with significant amplitude. In addition, we would have expected to see more arrivals from such an earthquake on other seismic stations in central Costa Rica. We therefore investigate whether the high-frequency arrivals may be the result of a deep seismic reflection from the subducting Cocos plate. The timing of these phases is consistent with a shear wave from Shot 21 that was reflected as a compressional (SxP) and a shear (SxS) wave at the top of the subducting Cocos slab between 35 and 55 km depth. The shift in dominant frequency from ~10 Hz in the downgoing seismic wave to ~20 Hz in the reflected waves requires a particular seismic structure at the interface between the subducting slab and the forearc mantle in order to produce a substantial increase in reflection coefficients with frequency. The spectral amplitude characteristics of the SxP and SxS phases from Shot 21 are consistent with a very high Vp/Vs ratio of 6 in ~5 m thick, slab-parallel layers. This result suggests that a system of thin shear zones near the plate interface beneath the forearc is occupied by hydrous fluids under near-lithostatic conditions. The overpressured shear zone probably takes up fluids from the downgoing slab, and it may control the lower limit of the seismogenic zone.This work was funded by the US National Science Foundation MARGINS programme

Current quality of life and its determinants among opiate-dependent individuals five years after starting methadone treatment

This study explores the current QoL of opiate-dependent individuals who started outpatient methadone treatment at least 5 years ago and assesses the influence of demographic, psychosocial, drug and health-related variables on individuals' QoL. Participants (n = 159) were interviewed about their current QoL, psychological distress and severity of drug-related problems, using the Lancashire Quality of Life Profile, the Brief Symptom Inventory and the Addiction Severity Index. Potential determinants of QoL were assessed in a multiple linear regression analysis. Five years after the start of methadone treatment, opiate-dependent individuals report low QoL scores on various domains. No association was found between drug-related variables and QoL, but a significant negative impact of psychological distress was identified. Severity of psychological distress, taking medication for psychological problems and the inability to change one's living situation were associated with lower QoL. Having at least one good friend and a structured daily activity had a significant, positive impact on QoL. Opiate-dependent individuals' QoL is mainly determined by their psychological well-being and a number of psychosocial variables. These findings highlight the importance of a holistic approach to treatment and support in methadone maintenance treatment, which goes beyond fixing the negative physical consequences of opiate dependence