The distinctive weathering crust habitat of a High Arctic glacier comprises discrete microbial micro-habitats

Sunlight penetrates the ice surfaces of glaciers and ice sheets, forming a water-bearing porous ice matrix known as the weathering crust. This crust is home to a significant microbial community. Despite the potential implications of microbial processes in the weathering crust for glacial melting, biogeochemical cycles, and downstream ecosystems, there have been few explorations of its microbial communities. In our study, we used 16S rRNA gene sequencing and shotgun metagenomics of a Svalbard glacier surface catchment to characterise the microbial communities within the weathering crust, their origins and destinies, and the functional potential of the weathering crust metagenome. Our findings reveal that the bacterial community in the weathering crust is distinct from those in upstream and downstream habitats. However, it comprises two separate micro-habitats, each with different taxa and functional categories. The interstitial porewater is dominated by Polaromonas, influenced by the transfer of snowmelt, and exported via meltwater channels. In contrast, the ice matrix is dominated by Hymenobacter, and its metagenome exhibits a diverse range of functional adaptations. Given that the global weathering crust area and the subsequent release of microbes from it are strongly responsive to climate projections for the rest of the century, our results underscore the pressing need to integrate the microbiome of the weathering crust with other communities and processes in glacial ecosystems.

Metagenome-assembled genomes from High Arctic glaciers highlight the vulnerability of glacier-associated microbiota and their activities to habitat loss

The rapid warming of the Arctic is threatening the demise of its glaciers and their associated ecosystems. Therefore, there is an urgent need to explore and understand the diversity of genomes resident within glacial ecosystems endangered by human-induced climate change. In this study we use genome-resolved metagenomics to explore the taxonomic and functional diversity of different habitats within glacier-occupied catchments. Comparing different habitats within such catchments offers a natural experiment for understanding the effects of changing habitat extent or even loss upon Arctic microbiota. Through binning and annotation of metagenome-assembled genomes (MAGs) we describe the spatial differences in taxon distribution and their implications for glacier-associated biogeochemical cycling. Multiple taxa associated with carbon cycling included organisms with the potential for carbon monoxide oxidation. Meanwhile, nitrogen fixation was mediated by a single taxon, although diverse taxa contribute to other nitrogen conversions. Genes for sulphur oxidation were prevalent within MAGs implying the potential capacity for sulphur cycling. Finally, we focused on cyanobacterial MAGs, and those within cryoconite, a biodiverse microbe-mineral granular aggregate responsible for darkening glacier surfaces. Although the metagenome-assembled genome of Phormidesmis priestleyi, the cyanobacterium responsible for forming Arctic cryoconite was represented with high coverage, evidence for the biosynthesis of multiple vitamins and co-factors was absent from its MAG. Our results indicate the potential for cross-feeding to sustain P. priestleyi within granular cryoconite. Taken together, genome-resolved metagenomics reveals the vulnerability of glacier-associated microbiota to the deletion of glacial habitats through the rapid warming of the Arctic.

Trace element, rare earth element and trace carbon compounds in Subglacial Lake Whillans, West Antarctica

Whillans Subglacial Lake (SLW) lies beneath 801 m of ice in the lower portion of the Whillans Ice Stream (WIS) in West Antarctica and is part of an extensive and active subglacial drainage network. Here, the geochemical characterization of SLW rare earth elements (REE), trace elements (TE), free amino acids (FAA), and phenolic compounds (PC) measured in lakewater and sediment porewater are reported. The results show, on average, higher values of REEs in the lakewater than in the porewater, and clear changes in all REE concentrations and select redox sensitive trace element concentrations in porewaters at a depth of ~15 cm in the 38 cm lake sediment core. This is consistent with prior results on the lake sediment redox conditions based on gas chemistry and microbiological data. Low concentrations of vanillyl phenols were measured in the SLW water column with higher concentrations in porewater samples and their concentration profiles in the sediments may also reflect changing redox conditions in the sediments. Vanillin concentrations increased with depth in the sediments as oxygenation decreases, while the concentrations of vanillic acid, the more oxidized component, were higher in the more oxygenated surface sediments. Collectively these results indicate redox changes occurring with the upper 38 cm of sediment in SLW and provide support for the existence of a seawater source, already hypothesized, in the sediments below the lowest measured depth, and of a complex and dynamic geochemical system beneath the West Antarctic Ice Sheet. Our results are the first to detail geochemical properties from an Antarctic subglacial environment using direct sampling technology. Due to their isolation from the wider environment, subglacial lakes represent one of our planets last pristine environments that provide habitats for microbial life and natural biogeochemical cycles but also impact the basal hydrology and can cause ice flow variations.

Storage and export of microbial biomass across the western Greenland Ice Sheet

The Greenland Ice Sheet harbours a wealth of microbial life, yet the total biomass stored or exported from its surface to downstream environments is unconstrained. Here, we quantify microbial abundance and cellular biomass flux within the near-surface weathering crust photic zone of the western sector of the ice sheet. Using groundwater techniques, we demonstrate that interstitial water flow is slow (~10⁻² m d⁻¹), while flow cytometry enumeration reveals this pathway delivers 5 × 10⁸ cells m⁻² d⁻¹ to supraglacial streams, equivalent to a carbon flux up to 250 g km⁻² d⁻¹. We infer that cellular carbon accumulation in the weathering crust exceeds fluvial export, promoting biomass sequestration, enhanced carbon cycling, and biological albedo reduction. We estimate that up to 37 kg km⁻² of cellular carbon is flushed from the weathering crust environment of the western Greenland Ice Sheet each summer, providing an appreciable flux to support heterotrophs and methanogenesis at the bed.

Microbes that colonise ice sheet surfaces are important to the carbon cycle, but their biomass and transport remains unquantified. Here, the authors reveal substantial microbial carbon fluxes across Greenland’s ice surface, in quantities that may sustain subglacial heterotrophs and fuel methanogenesis.

Thermodynamic and Kinetic Parameters for Calcite Nucleation on Peptoid and Model Scaffolds: A Step toward Nacre Mimicry

The production of novel composite materials, assembled using biomimetic polymers known as peptoids (N-substituted glycines) to nucleate CaCO₃, can open new pathways for advanced material design. However, a better understanding of the heterogeneous CaCO₃ nucleation process is a necessary first step. We determined the thermodynamic and kinetic parameters for calcite nucleation on self-assembled monolayers (SAMs) of nanosheet-forming peptoid polymers and simpler, alkanethiol analogues. We used nucleation rate studies to determine the net interfacial free energy (γ _net) for the peptoid-calcite interface and for SAMs terminated with carboxyl headgroups, amine headgroups, or a mix of the two. We compared the results with γ _net determined from dynamic force spectroscopy (DFS) and from density functional theory (DFT), using COSMO-RS simulations. Calcite nucleation has a lower thermodynamic barrier on the peptoid surface than on carboxyl and amine SAMs. From the relationship between nucleation rate (J ₀) and saturation state, we found that under low-saturation conditions, i.e. <3.3 (pH 9.0), nucleation on the peptoid substrate was faster than that on all of the model surfaces, indicating a thermodynamic drive toward heterogeneous nucleation. When they are taken together, our results indicate that nanosheet-forming peptoid monolayers can serve as an organic template for CaCO₃ polymorph growth.

P2669Prognostication in out-of-hospital cardiac arrest

Background

Out-of-hospital cardiac arrest (OOHCA) remains an area where little progress has been made in outcomes despite significant advances in cardiac care. The OOHCA cohort requires a large amount of resources, including primary coronary intervention and intensive care, often with poor eventual outcomes. A clinical prognostic scoring system would allow resources to be focused on OOHCA patients who are likely to survive; rather than expensive and futile treatments in those who are not. Several different scoring systems have been published but have not been compared in a real world cohort of OOHCA patients.

Method

The Cardiac Arrest Hospital Prognosis (CAHP) score that utilises 7 variables and a simpler three-factor prognostic score derived by Hirt et al were applied retrospectively to a cohort of 157 consecutive OOHCA patients presenting to a regional Centre in our city, UK between 2016 and 2018. For each patient the CAHP score was calculated where a score of >200 predicts a Cerebral Performance Category (CPC) outcome of 3–5 (severe disability, vegetative coma or death). They were also categorised using the Hirt algorithm into “Futile”, “Approaching Futility” and “Non-Futile” groups. CPC outcomes were then compared using both scores and diagnostic accuracy assessed.

Results

A CAHP score of >200 predicted a CPC outcome of 3–5 with 97% specificity and a positive predictive value of 92%. A CAHP score >200 predicted 30-day mortality with 96% specificity, and a positive predictive value of 89% (Fig. 1A). The same cohort categorised by the Hirt algorithm was less accurate; in those patients sorted into the “futile” category 15% of patients survived, and in the “approaching futility” group survival was 100% (Fig. 1B). The specificity and PPV of predicting futility was 94% and 85% respectively.

Conclusion

Although a simple three-factor prognostic score as suggested by Hirt et al is attractive in this cohort of OOHCA patients it did not discriminate those patients who were likely to survive and, the CAHP score was more accurate in predicting outcome. Further validation is required in prospective, multi-centre studies to ensure that application of these scores are reproducible in real-world OOHCA populations in decision making for emergency coronary angiography.

Acknowledgement/Funding

None

Accelerometery and Heart Rate Responses of Professional Fast-Medium Bowlers in One-Day and Multi-Day Cricket

The physical demands of fast-medium bowling are increasingly being recognised, yet comparative exploration of the differing demands between competitive formats (i.e. one-day [OD] versus multi-day [MD] matches) remain minimal. The aim of this study was to describe in-match physiological profiles of professional fast-medium bowlers from England across different versions of competitive matches using a multivariable wearable monitoring device. Seven professional cricket fast-medium bowlers wore the Bioharness^TM monitoring device during matches, over three seasons (>80 hours in-match). Heart Rate (HR) and Acceleromety (ACC) was compared across match types (OD, MD) and different in-match activity states (Bowling, Between over bowling, Fielding). Peak acceleration during OD bowling was significantly higher in comparison to MD cricket ([OD vs. MD] 234.1 ± 57.9 vs 226.6 ± 32.9 ct·episode^-1, p < 0.05, ES = 0.11-0.30). Data for ACC were also higher during OD than MD fielding activities (p < 0.01, ES = 0.11-.30). OD bowling stimulated higher mean HR responses (143 ± 14 vs 137 ± 16 beats·min^-1, p < 0.05, ES = 0.21) when compared to MD matches. This increase in OD cricket was evident for both between over (129 ± 9 vs 120 ± 13 beats·min^-1,p < 0.01, ES = 0.11-0.50) and during fielding (115 ± 12 vs 106 ± 12 beats·min^-1, p < 0.01, ES = 0.36) activity. The increased HR and ACC evident in OD matches suggest greater acute physical loads than MD formats. Therefore, use of wearable technology and the findings provided give a valuable appreciation of the differences in match loads, and thus required physiological preparation and recovery in fast-medium bowlers.

Physiological Ecology of Microorganisms in Subglacial Lake Whillans

Subglacial microbial habitats are widespread in glaciated regions of our planet. Some of these environments have been isolated from the atmosphere and from sunlight for many thousands of years. Consequently, ecosystem processes must rely on energy gained from the oxidation of inorganic substrates or detrital organic matter. Subglacial Lake Whillans (SLW) is one of more than 400 subglacial lakes known to exist under the Antarctic ice sheet; however, little is known about microbial physiology and energetics in these systems. When it was sampled through its 800 m thick ice cover in 2013, the SLW water column was shallow (~2 m deep), oxygenated, and possessed sufficient concentrations of C, N, and P substrates to support microbial growth. Here, we use a combination of physiological assays and models to assess the energetics of microbial life in SLW. In general, SLW microorganisms grew slowly in this energy-limited environment. Heterotrophic cellular carbon turnover times, calculated from ³H-thymidine and ³H-leucine incorporation rates, were long (60 to 500 days) while cellular doubling times averaged 196 days. Inferred growth rates (average ~0.006 d^-1) obtained from the same incubations were at least an order of magnitude lower than those measured in Antarctic surface lakes and oligotrophic areas of the ocean. Low growth efficiency (8%) indicated that heterotrophic populations in SLW partition a majority of their carbon demand to cellular maintenance rather than growth. Chemoautotrophic CO₂-fixation exceeded heterotrophic organic C-demand by a factor of ~1.5. Aerobic respiratory activity associated with heterotrophic and chemoautotrophic metabolism surpassed the estimated supply of oxygen to SLW, implying that microbial activity could deplete the oxygenated waters, resulting in anoxia. We used thermodynamic calculations to examine the biogeochemical and energetic consequences of environmentally imposed switching between aerobic and anaerobic metabolisms in the SLW water column. Heterotrophic metabolisms utilizing acetate and formate as electron donors yielded less energy than chemolithotrophic metabolisms when calculated in terms of energy density, which supports experimental results that showed chemoautotrophic activity in excess of heterotrophic activity. The microbial communities of subglacial lake ecosystems provide important natural laboratories to study the physiological and biogeochemical behavior of microorganisms inhabiting cold, dark environments.

Subglacial Lake Whillans microbial biogeochemistry: a synthesis of current knowledge

Liquid water occurs below glaciers and ice sheets globally, enabling the existence of an array of aquatic microbial ecosystems. In Antarctica, large subglacial lakes are present beneath hundreds to thousands of metres of ice, and scientific interest in exploring these environments has escalated over the past decade. After years of planning, the first team of scientists and engineers cleanly accessed and retrieved pristine samples from a West Antarctic subglacial lake ecosystem in January 2013. This paper reviews the findings to date on Subglacial Lake Whillans and presents new supporting data on the carbon and energy metabolism of resident microbes. The analysis of water and sediments from the lake revealed a diverse microbial community composed of bacteria and archaea that are close relatives of species known to use reduced N, S or Fe and CH4 as energy sources. The water chemistry of Subglacial Lake Whillans was dominated by weathering products from silicate minerals with a minor influence from seawater. Contributions to water chemistry from microbial sulfide oxidation and carbonation reactions were supported by genomic data. Collectively, these results provide unequivocal evidence that subglacial environments in this region of West Antarctica host active microbial ecosystems that participate in subglacial biogeochemical cycling.

Microbial sulfur transformations in sediments from Subglacial Lake Whillans

Diverse microbial assemblages inhabit subglacial aquatic environments. While few of these environments have been sampled, data reveal that subglacial organisms gain energy for growth from reduced minerals containing nitrogen, iron, and sulfur. Here we investigate the role of microbially mediated sulfur transformations in sediments from Subglacial Lake Whillans (SLW), Antarctica, by examining key genes involved in dissimilatory sulfur oxidation and reduction. The presence of sulfur transformation genes throughout the top 34 cm of SLW sediments changes with depth. SLW surficial sediments were dominated by genes related to known sulfur-oxidizing chemoautotrophs. Sequences encoding the adenosine-5'-phosphosulfate (APS) reductase gene, involved in both dissimilatory sulfate reduction and sulfur oxidation, were present in all samples and clustered into 16 distinct operational taxonomic units. The majority of APS reductase sequences (74%) clustered with known sulfur oxidizers including those within the "Sideroxydans" and Thiobacillus genera. Reverse-acting dissimilatory sulfite reductase (rDSR) and 16S rRNA gene sequences further support dominance of "Sideroxydans" and Thiobacillus phylotypes in the top 2 cm of SLW sediments. The SLW microbial community has the genetic potential for sulfate reduction which is supported by experimentally measured low rates (1.4 pmol cm(-3)d(-1)) of biologically mediated sulfate reduction and the presence of APS reductase and DSR gene sequences related to Desulfobacteraceae and Desulfotomaculum. Our results also infer the presence of sulfur oxidation, which can be a significant energetic pathway for chemosynthetic biosynthesis in SLW sediments. The water in SLW ultimately flows into the Ross Sea where intermediates from subglacial sulfur transformations can influence the flux of solutes to the Southern Ocean.

Bacterially induced calcium carbonate precipitation and strontium coprecipitation in a porous media flow system

Strontium-90 is a principal radionuclide contaminant in the subsurface at several Department of Energy sites in the Western U.S., causing a threat to groundwater quality in areas such as Hanford, WA. In this work, we used laboratory-scale porous media flow cells to examine a potential remediation strategy employing coprecipitation of strontium in carbonate minerals. CaCO(3) precipitation and strontium coprecipitation were induced via ureolysis by Sporosarcina pasteurii in two-dimensional porous media reactors. An injection strategy using pulsed injection of calcium mineralization medium was tested against a continuous injection strategy. The pulsed injection strategy involved periods of lowered calcite saturation index combined with short high fluid velocity flow periods of calcium mineralization medium followed by stagnation (no-flow) periods to promote homogeneous CaCO(3) precipitation. By alternating the addition of mineralization and growth media the pulsed strategy promoted CaCO(3) precipitation while sustaining the ureolytic culture over time. Both injection strategies achieved ureolysis with subsequent CaCO(3) precipitation and strontium coprecipitation. The pulsed injection strategy precipitated 71-85% of calcium and 59% of strontium, while the continuous injection was less efficient and precipitated 61% of calcium and 56% of strontium. Over the 60 day operation of the pulsed reactors, ureolysis was continually observed, suggesting that the balance between growth and precipitation phases allowed for continued cell viability. Our results support the pulsed injection strategy as a viable option for ureolysis-induced strontium coprecipitation because it may reduce the likelihood of injection well accumulation caused by localized mineral plugging while Sr coprecipitation efficiency is maintained in field-scale applications.

Potential CO2 leakage reduction through biofilm-induced calcium carbonate precipitation

Mitigation strategies for sealing high permeability regions in cap rocks, such as fractures or improperly abandoned wells, are important considerations in the long term security of geologically stored carbon dioxide (CO(2)). Sealing technologies using low-viscosity fluids are advantageous in this context since they potentially reduce the necessary injection pressures and increase the radius of influence around injection wells. Using aqueous solutions and suspensions that can effectively promote microbially induced mineral precipitation is one such technology. Here we describe a strategy to homogenously distribute biofilm-induced calcium carbonate (CaCO(3)) precipitates in a 61 cm long sand-filled column and to seal a hydraulically fractured, 74 cm diameter Boyles Sandstone core. Sporosarcina pasteurii biofilms were established and an injection strategy developed to optimize CaCO(3) precipitation induced via microbial urea hydrolysis. Over the duration of the experiments, permeability decreased between 2 and 4 orders of magnitude in sand column and fractured core experiments, respectively. Additionally, after fracture sealing, the sandstone core withstood three times higher well bore pressure than during the initial fracturing event, which occurred prior to biofilm-induced CaCO(3) mineralization. These studies suggest biofilm-induced CaCO(3) precipitation technologies may potentially seal and strengthen fractures to mitigate CO(2) leakage potential.

Engineered applications of ureolytic biomineralization: a review

Microbially-induced calcium carbonate (CaCO3) precipitation (MICP) is a widely explored and promising technology for use in various engineering applications. In this review, CaCO3 precipitation induced via urea hydrolysis (ureolysis) is examined for improving construction materials, cementing porous media, hydraulic control, and remediating environmental concerns. The control of MICP is explored through the manipulation of three factors: (1) the ureolytic activity (of microorganisms), (2) the reaction and transport rates of substrates, and (3) the saturation conditions of carbonate minerals. Many combinations of these factors have been researched to spatially and temporally control precipitation. This review discusses how optimization of MICP is attempted for different engineering applications in an effort to highlight the key research and development questions necessary to move MICP technologies toward commercial scale applications.

Role of outer membrane c-type cytochromes MtrC and OmcA in Shewanella oneidensis MR-1 cell production, accumulation, and detachment during respiration on hematite

The iron-reducing bacterium Shewanella oneidensis MR-1 has the capacity to contribute to iron cycling over the long term by respiring on crystalline iron oxides such as hematite when poorly crystalline phases are depleted. The ability of outer membrane cytochromes OmcA and MtrC of MR-1 to bind to and transfer electrons to hematite has led to the suggestion that they function as terminal reductases when this mineral is used as a respiratory substrate. Differences in their redox behavior and hematite-binding properties, however, indicate that they play different roles in the electron transfer reaction. Here, we investigated how these differences in cytochrome behavior with respect to hematite affected biofilm development when the mineral served as terminal electron acceptor (TEA). Upon attachment to hematite, cells of the wild-type (WT) strain as well as those of a ΔomcA mutant but not those of a ΔmtrC mutant replicated and accumulated on the mineral surface. The results indicate that MtrC but not OmcA is required for growth when this mineral serves as TEA. While an OmcA deficiency did not impede cell replication and accumulation on hematite prior to achievement of a maximum surface cell density comparable to that established by WT cells, OmcA was required for efficient electron transfer and cell attachment to hematite once maximum surface cell density was achieved. OmcA may therefore play a role in overcoming barriers to electron transfer and cell attachment to hematite imposed by reductive dissolution of the mineral surface from cell respiration associated with achievement of high surface cell densities.

Methanogenesis in subglacial sediments

Methanogenic archaea have a unique role in Earth's global carbon cycle as producers of the greenhouse gas methane (CH4 ). However, despite the fact that ice covers 11% of Earth's continental landmass, evidence for methanogenic activity in subglacial environments has yet to be clearly demonstrated. Here we present genetic, biochemical and geochemical evidence indicative of an active population of methanogens associated with subglacial sediments from Robertson Glacier (RG), Canadian Rockies. Porewater CH4 was quantified in two subglacial sediment cores at concentrations of 16 and 29 ppmv. Coenzyme M (CoM), a metabolic biomarker for methanogens, was detected at a concentration of 1.3 nmol g sediment(-1) corresponding to ∼3 × 10(3) active cells g sediment(-1) . Genetic characterization of communities associated with subglacial sediments indicated the presence of several archaeal 16S rRNA and methyl CoM reductase subunit A (mcrA) gene phylotypes, all of which were affiliated with the euryarchaeal order Methanosarcinales. Further, CH4 was produced at 9-51 fmol g dry weight sediment(-1)  h(-1) in enrichment cultures of RG sediments incubated at 4°C. Collectively, these findings have important implications for the global carbon cycle in light of recent estimates indicating that the Earth's subglacial biome ranges from 10(4) to 10(6)  km(3) sediment.

Interior structure of neptune: comparison with uranus

Measurements of rotation rates and gravitational harmonics of Neptune made with the Voyager 2 spacecraft allow tighter constraints on models of the planet's interior. Shock measurements of material that may match the composition of Neptune, the so-calied planetary ;;ice,'' have been carried out to pressures exceeding 200 gigapascals (2 megabars). Comparison of shock data with inferred pressure-density profiles for both Uranus and Neptune shows substantial similarity through most of the mass of both planets. Analysis of the effect of Neptune's strong differential rotation on its gravitational harmonics indicates that differential rotation involves only the outermost few percent of Neptune's mass.

Microbially enhanced carbon capture and storage by mineral-trapping and solubility-trapping

The potential of microorganisms for enhancing carbon capture and storage (CCS) via mineral-trapping (where dissolved CO(2) is precipitated in carbonate minerals) and solubility trapping (as dissolved carbonate species in solution) was investigated. The bacterial hydrolysis of urea (ureolysis) was investigated in microcosms including synthetic brine (SB) mimicking a prospective deep subsurface CCS site with variable headspace pressures [p(CO(2))] of (13)C-CO(2). Dissolved Ca(2+) in the SB was completely precipitated as calcite during microbially induced hydrolysis of 5-20 g L(-1) urea. The incorporation of carbonate ions from (13)C-CO(2) ((13)C-CO(3)(2-)) into calcite increased with increasing p((13)CO(2)) and increasing urea concentrations: from 8.3% of total carbon in CaCO(3) at 1 g L(-1) to 31% at 5 g L(-1), and 37% at 20 g L(-1). This demonstrated that ureolysis was effective at precipitating initially gaseous [CO(2)(g)] originating from the headspace over the brine. Modeling the change in brine chemistry and carbonate precipitation after equilibration with the initial p(CO(2)) demonstrated that no net precipitation of CO(2)(g) via mineral-trapping occurred, since urea hydrolysis results in the production of dissolved inorganic carbon. However, the pH increase induced by bacterial ureolysis generated a net flux of CO(2)(g) into the brine. This reduced the headspace concentration of CO(2) by up to 32 mM per 100 mM urea hydrolyzed because the capacity of the brine for carbonate ions was increased, thus enhancing the solubility-trapping capacity of the brine. Together with the previously demonstrated permeability reduction of rock cores at high pressure by microbial biofilms and resilience of biofilms to supercritical CO(2), this suggests that engineered biomineralizing biofilms may enhance CCS via solubility-trapping, mineral formation, and CO(2)(g) leakage reduction.

Selective detection of luminescence from semiconductor quantum dots by nanosecond time-gated imaging with a colour-masked CCD detector

Quantum dots are of considerable interest as highly detectable labels with broad absorption, narrow spectral emission and good quantum yields. The luminescence emission has a longer decay time than that of the most common fluorophores, leading to facile rejection of much background emission (such as autofluorescence from biological samples) by means of gated detection. Here, it is shown that a new technique, true-colour nanosecond time-gated luminescence imaging, can be used for selective detection of quantum dot luminescence and should prove valuable for multiplexed detection on the basis of both spectral emission profile and luminescence decay time.

Prospects for applications of lanthanide-based upconverting surfaces to bioassay and detection

Biological assays to detect binding interactions are often conducted using fluorescence resonance energy transfer (FRET) but this has several disadvantages that markedly reduce the dynamic range of measurements. The very short range of FRET interactions also causes difficulties when large analytes such as viruses or spores are to be detected. Conventional FRET-based assays can in principle be improved using infrared-excited upconverting lanthanide-based energy donors but this does not address the short range of the FRET process. Here we investigate an alternative mode of energy transfer based on evanescent wave coupling from an erbium-doped waveguide to an absorbed fluorophore and characterise the luminescence from the dopant. The upconverted erbium emission is highly structured with well-separated bands in the violet, green and red spectral regions and very little detectable signal between the peaks. The relative intensity of these bands depends on power-density of infrared excitation. Green emission predominates at low power-density and red emission increases more rapidly as power-density increases, with a smaller violet peak also emerging. The temporal response of the upconverting material to pulsed infrared excitation was investigated and was shown to vary markedly with emission wavelength with the red component being particularly sensitive to the duration of the excitation pulse. A surface monolayer of the fluorescent protein R-phycoerythrin was very easily detected on binding to an upconverting waveguide. The potential advantages and limitations of the evanescent wave excitation technique for fluorescence detection are discussed and avenues for further development are considered.

Total internal reflection fluorescence imaging using an upconverting cover slip for multicolour evanescent excitation

Total internal reflection fluorescence microscopy is well known as a means of studying surface-bound structures in cell biology. It is usually measured either by coupling a light source to the sample using a prism or with a special objective where light passing through the periphery of the lens illuminates the contact region beyond the critical angle. In this study we present a new and simple approach to total internal reflection fluorescence microscopy where the sample is mounted on a cover slip prepared from a high-index upconverting glass-ceramic. Excitation of the cover slip with a low-cost near-infrared laser diode generates intense narrow-band visible emission within the cover slip, some of which is totally internally reflected. This emission gives rise to an evanescent wave at the interface and hence can excite surface-bound fluorescent species. Depending on the excitation conditions the cover slip can generate violet, green and red emission and hence can excite a wide range of fluorescent labels. Fluorescence emission from the sample can be detected in spectral regions where the direct emission from the cover slip is very weak. The advantages and limitations of the technique are discussed in comparison with conventional total internal reflection fluorescence microscopy measurements and prospects for novel total internal reflection fluorescence microscopy geometries are considered.

Effect of strontium contaminants upon the size and solubility of calcite crystals precipitated by the bacterial hydrolysis of urea

The nucleation and growth of calcite precipitates induced by the bacterial hydrolysis of urea (ureolysis) from a Sr-contaminant inclusive, and a Sr-free artificial groundwater (AGW) mimicking the composition of the 90Sr contaminated Snake River Plain aquifer were investigated. Sr-free experiments exhibited a gradual increase in mean calcite crystal diameter (<1000 nm) from day (D) 1 to 6, while in the Sr-inclusive experiments, daily diameters were approximately constant from D1 to D6, and crystals were smaller (mean <840 nm). These data demonstrate a steady state had been attained early in the Sr-inclusive experiments from growth inhibition by Sr. Modeling of the crystal growth mechanisms on the USGS GALOPER software suggested crystal size distributions in the Sr-inclusive and Sr-free experiments were generated in the nucleation stage by a decreasing nucleation rate with surface-controlled growth, followed by supply-controlled and random growth. This occurred despite the availability of Ca2+ and HCO3-, implying crystal growth is limited bythe rate of solute advection to the crystal surface. Calculation of the solubility constant (In KsO(A)) demonstrates smaller crystals are more soluble, reflecting a higher molar surface area. The coprecipitation of Sr therefore generates smaller and thus more soluble crystals. However, this is unlikely to dramatically reduce the long-term effectiveness of Sr immobilization because when crystal growth had ceased in the Sr-inclusive AGW, > 99% of calcite precipitated and Sr coprecipitated occurred in large crystals with a low solubility.

Metallization of fluid nitrogen and the mott transition in highly compressed low-Z fluids

Electrical conductivities are reported for degenerate fluid nitrogen at pressures up to 180 GPa (1.8 Mbar) and temperatures of approximately 7000 K. These extreme quasi-isentropic conditions were achieved with multiple-shock compression generated with a two-stage light-gas gun. Nitrogen undergoes a nonmetal-metal transition at 120 GPa, probably in the monatomic state. These N data and previous conductivity data for H, O, Cs, and Rb are used to develop a general picture of the systematics of the nonmetal-metal transition in these fluids. Specifically, the density dependences of electrical conductivities in the semiconducting fluid are well correlated with the radial extent of the electronic charge-density distributions of H, N, O, Cs, and Rb atoms. These new data for N scale with previous data for O, as expected from their similar charge-density distributions.

Measurement of nanosecond time-resolved fluorescence with a directly gated interline CCD camera

CCD cameras coupled optically to gated image intensifiers have been used for fast time-resolved measurements for some years. Image intensifiers have disadvantages, however, and for some applications it would be better if the image sensor could be gated directly at high speed. Control of the 'charge drain' function on an interline-transfer CCD allows the sensor to be switched rapidly from an insensitive state. The temporal and spatial properties of the charge drain are explored in the present paper and it is shown that nanosecond time resolution with acceptable spatial uniformity can be achieved for a small commercial sensor. A fluorescence lifetime imaging system is demonstrated, based on a repetitively pulsed laser excitation source synchronized to the CCD control circuitry via a programmable delay unit.

Direct modulation of the effective sensitivity of a CCD detector: a new approach to time-resolved fluorescence imaging

In this paper a novel approach to frequency-domain fluorescence lifetime imaging (FLIM) is described. In a CCD camera a single pixel is defined by a charge pattern on a group of electrodes. By modulation of the pattern of voltages defining the pixel structure it is possible to modulate the sensitivity of the CCD at radio frequency. The modulation enhances the noise performance of the CCD, in contrast to the deterioration in performance seen when an intensifier stage is similarly modulated. The new technology has potential applications to a wide range of assays as well as in conventional FLIM applications. Unlike intensifier-based systems, the directly modulated CCD is physically small, inexpensive, robust and offers superior resolution and noise performance.

An unusual case of chronic neuropathic pain responds to an optimum frequency of intravenous ketamine infusions

The effective treatment of patients suffering from a variety of difficult pain syndromes, including phantom pain and other neuropathic pains, remains a clinical challenge. Neuropathic pain has been shown to respond to drugs that block the N-methyl-D-aspartate (NMDA) receptor, such as ketamine and amantidine. A 44-year-old woman with a previous right-sided forequarter amputation presented to the Palliative Medicine Team complaining of neuropathic pain in her left arm, which was neurologically intact. The pain was treated with repeated infusions of intravenous ketamine. Twenty-one infusions were given over a period of four months. The pain intensity experienced by the patient lessened as the frequency of the ketamine infusions increased. This finding has not been described previously and supports the theory that there may be an optimum frequency of ketamine infusions to achieve adequate pain control.

High pressure insulator-metal transition in molecular fluid oxygen

We report the first experimental evidence for a metallic phase in fluid molecular oxygen. Our electrical conductivity measurements of fluid oxygen under dynamic quasi-isentropic compression show that a nonmetal-metal transition occurs at 3.4 fold compression, 4500 K, and 1.2 Mbar. We discuss the main features of the electrical conductivity dependence on density and temperature and give an interpretation of the nature of the electrical transport mechanisms in fluid oxygen at these extreme conditions.

Fast laser-induced solute release from liposomes sensitized with photochromic lipid: effects of temperature, lipid host, and sensitizer concentration

Liposomes of gel-phase phospholipid have been prepared containing a photochromic lipid sensitizer. A fast UV laser pulse isomerizes the sensitizer destabilizing the lipid bilayer structure and causing release of trapped solute. The kinetics of solute release have been investigated as a function of host lipid chain length, sensitizer concentration, and temperature, and the limits of liposome stability have been established. At low concentrations of sensitizer, pulsed laser irradiation induces some solute release when continuous UV illumination is ineffective. Although rates of solute release usually increase with temperature, at low sensitizer concentration in a rigid host, leakage at first increases but then decreases rapidly above a threshold temperature. The results presented are relevant to the design of photostimulated drug delivery systems and to potential applications of photosensitive liposomes as caging agents for biological effectors.

Metallization and electrical conductivity of hydrogen in Jupiter

Electrical conductivities of molecular hydrogen in Jupiter were calculated by scaling electrical conductivities measured at shock pressures in the range of 10 to 180 gigapascals (0.1 to 1.8 megabars) and temperatures to 4000 kelvin, representative of conditions inside Jupiter. Jupiter's magnetic field is caused by convective dynamo motion of electrically conducting fluid hydrogen. The data imply that Jupiter should become metallic at 140 gigapascals in the fluid, and the electrical conductivity in the jovian molecular envelope at pressures up to metallization is about an order of magnitude larger than expected previously. The large magnetic field is produced in the molecular envelope closer to the surface than previously thought.

Fluorescence lifetime imaging: an emerging technique in fluorescence microscopy

Fluorescence microscopy is an important tool for biological research, in part because of the extremely high detection sensitivity that can be achieved, but also because fluorescent molecules can be used as probes on account of their environmental responsiveness, for example to measure intracellular pH or metal ion concentration. Unfortunately, the environmental sensitivity can sometimes be a source of problems because of enhancement or 'quenching', which can make it very difficult to relate emission intensity to the amount of fluorophore present. The measured intensity is essentially proportional to the product of the amount of fluorophore present in the sample and the local quantum yield of the fluorophore (the quantum yield can be thought of as the probability that an excited molecule decays by fluorescence emission rather than by other non-radiative processes). This is a particular difficulty in an environment such as a cell or tissue slice in which quantum yield and flurophore concentration can both vary within the sample. Ideally we would wish to be able to measure the quantum yield of fluorescence as well as the fluorescence intensity, as this would allow environmental effects to be compensated for. Unfortunately, this is not at all easy, and indirect means to achieve the same goal are more appropriate. A recently introduced technique, fluorescence lifetime imaging (Morgan et al. 1992, Wang et al. 1992), offers one such means to improve quantification of fluorescence microscopy. In addition, as will be explained, the technique offers the prospect of significantly improving detection sensitivity in appropriate circumstances.

Fast solute release from photosensitive liposomes: an alternative to 'caged' reagents for use in biological systems

The kinetics of release of soluble marker trapped in liposomes of gel phase phospholipid containing a photoisomerisable phospholipid analogue have been investigated. Marker release is triggered by UV laser flash photolysis at 355 nm. A markedly temperature-dependent release rate is seen, and above 25 degrees C millisecond release kinetics can be achieved. These results suggest that such liposomes might find application as an alternative to conventional 'caged' reagents for photo-triggered reagent release in biological research.

Liposome fusion and lipid exchange on ultraviolet irradiation of liposomes containing a photochromic phospholipid

A photochromic phospholipid, 1,2-bis[4-4(4-n-butylphenylazo) phenylbutyroyl] phosphatidylcholine (Bis-Azo PC) has been incorporated into liposomes of gel- and liquid-crystalline- phase phospholipids. Liposomes of gel-phase phospholipid are stable in the presence of the trans photostationary state Bis-Azo PC and can encapsulate fluorescent marker dye. On photoisomerization to the cis photostationary state, trapped marker is rapidly released. Liposomes containing Bis-Azo PC can rapidly fuse together after UV isomerization, this process continuing in the dark. Exposure to white light causes reversion of Bis-Azo Pc to the trans form and halts dye leakage and vesicle fusion. Both unilamellar and multilamellar liposomes are able to fuse together on UV exposure. On UV photolysis, liposomes containing Bis-Azo PC do not fuse with a large excess of unlabeled liposomes, but transfer of Bis-Azo PC can be demonstrated spectrophotometrically. Vesicles of pure gel-phase lipid containing trapped marker dye but initially no Bis-Azo PC become leaky as a result of this lipid transfer. Liposomes composed of liquid-crystalline-phase phosphatidylcholine- containing Bis-Azo PC neither leak trapped marker no fuse together on photolysis, nor do liquid-crystalline-phase liposomes fuse with gel-phase liposomes under these conditions. These results are discussed together with some possible applications of liposome photodestabilization.

Education of Nursing Students With Special Needs

Recent legislation such as the Americans with Disabilities Act will have a significant impact on higher education in nursing. A survey was conducted to describe the extent to which BSN and ADN nursing programs in the United States admit and graduate special needs and chronically ill students, and to identify the accommodations which have been successful in providing nursing education to these students. Responses received from 86 schools of nursing in 44 states indicated that most schools have had contact with students with special needs such as visual, hearing, or mobility impairments, learning disabilities, and mental or chronic illnesses. Learning disabilities and mental impairment were cited most frequently as having been present among the student population. Few programs have had experience with students with vision problems. While most programs responding had little experience with providing special accommodations to special needs students, most were aware of accessibility on their campuses. Recent legislation aimed at creating opportunities for disabled individuals to successfully enter the work force creates challenges for schools of nursing in education of students with special needs. Issues are raised that must be addressed to meet this important challenge.

The Nature of the Interior of Uranus Based on Studies of Planetary Ices at High Dynamic Pressure

Data from the Voyager II spacecraft showed that Uranus has a large magnetic field with geometry similar to an offset tilted dipole. To interpret the origin of the magnetic field, measurements were made of electrical conductivity and equation-of-state data of the planetary "ices" ammonia, methane, and "synthetic Uranus" at shock pressures and temperatures up to 75 gigapascals and 5000 K. These pressures and temperatures correspond to conditions at the depths at which the surface magnetic field is generated. Above 40 gigapascals the conductivities of synthetic Uranus, water, and ammonia plateau at about 20(ohm-cm)(-1), providing an upper limit for the electrical conductivity used in kinematic or dynamo calculations. The nature of materials at the extreme conditions in the interior is discussed.

Light-induced fusion of liposomes with release of trapped marker dye is sensitised by photochromic phospholipid

Liposomes have been prepared from dipalmitoylphosphatidylcholine containing small amounts of a synthetic photochromic phospholipid, 'Bis-Azo PC'. In the dark, these are stable at room temperature, and contents do not significantly leak over weeks. Photoisomerisation results in immediate release of trapped marker, and in liposome fusion to form larger structures. Fusion has been detected using a fluorescence polarisation assay, and confirmed by electron microscopy. In mixtures, fusion occurs between 'photochromic' liposomes and those of pure lipid. Bis-Azo PC contains two photochromic acyl chains; analogues bearing a single photochromic chain appear to have little effect on bilayer permeability after isomerisation. Photo-induced leakage and liposome fusion suggest possible applications for localised drug delivery as an adjunct to phototherapy. The ability to non-invasively trigger fusion processes should be useful in fundamental studies of membrane interactions. We believe this to be the first report of photo-induced fusion to date.

Responsibility of the obstetrician to the fetus. II. Influence of prepregnancy weight and pregnancy weight gain on birthweight

The diet of pregnant women has been restricted in various ways since earliest history. Dietary restriction may have severely deleterious effects on the fetus. Our study revealed a positive correlation of prepregnancy weight and pregnancy weight gain to term infant birthweight. Their influences are independent and additive. It is of the utmost importance to the fetus and the future of the human race that the diet of pregnant women contain the caloric value and essential nutrients recommended by the National Research Council.