Metal-rich Environments Research Articles

The response of epilithic bacteria to different metals regime in two upland streams: assessed by conventional microbiological methods and PCR-DGGE

The epilithic bacterial community in the zinc-contaminated River West Allen, northeast England, was compared to that in the less contaminated River East Allen. Bacterial abundance (DAPI counts) and activity (leucine assimilation rate) were similar in the two streams, suggesting the possibility that a tolerant community had developed in the West Allen. Despite the similarity in abundance and activity, molecular genomic methods (PCR-DGGE) showed that the epilithic bacterial communities were consistently different between the two streams, and that bacterial diversity was greater in the zinc-contaminated West Allen. Sequencing of DGGE bands indicated that α-Proteobacteria and Nitrospirae, previously associated with metal-rich environments, were present in the West Allen. This may support the suggestion that a metal-tolerant bacterial community had developed at the zinc-contaminated site.

Survey for Transiting Extrasolar Planets in Stellar Systems. II. Spectrophotometry and Metallicities of Open Clusters

We present metallicity estimates for seven open clusters based on spectrophotometric indices from moderate-resolution spectroscopy. Observations of field giants of known metallicity provide a correlation between the spectroscopic indices and the metallicity of open cluster giants. We use χ2 analysis to fit the relation of spectrophotometric indices to metallicity in field giants. The resulting function allows an estimate of the target-cluster giants' metallicities with an error in the method of ±0.08 dex. We derive the following metallicities for the seven open clusters: NGC 1245, [M/H] = -0.14 ± 0.04; NGC 2099, [M/H] = +0.05 ± 0.05; NGC 2324, [M/H] = -0.06 ± 0.04; NGC 2539, [M/H] = -0.04 ± 0.03; NGC 2682 (M67), [M/H] = -0.05 ± 0.02; NGC 6705, [M/H] = +0.14 ± 0.08; NGC 6819, [M/H] = -0.07 ± 0.12. These metallicity estimates will be useful in planning future extrasolar planet transit searches, since planets may form more readily in metal-rich environments.

Instrument development to search for biomarkers on mars: Terrestrial acidophile, iron-powered chemolithoautotrophic communities as model systems

Recent findings by the MER rover opportunity confirming the presence of iron minerals that can only be formed in the presence of water emphasize the study of analogous environments to Mars on Earth. The study of chemolithoautotrophic communities living in acidic iron-rich habitats is highly relevant in order to identify Mars analog environment-specific biomarkers. Iron oxidizing bacteria like Leptospirillum ferrooxidans and Acidithiobacillus ferrooxidans have ways of life for which it is feasible to identify a past or present hypothetical niche on Mars. We have developed a strategy for biomarker identification based on: (i) search for biosignatures on acid and metal-rich environments; (ii) development of an immunosensor microarray; and (iii) integration into an instrument for autonomous and remote operation. The instrument that we have built, called Signs Of LIfe Detector (SOLID), is capable of processing a variety of samples for the detection of specific biomarkers. Antibodies against several bacterial strains have been developed and tested in a microarray biosensor on SOLID. Tests with field samples have been successfully performed, allowing the detection of L. ferrooxidans, A. ferrooxidans present in sediment samples.

Growth in sulfidic mineral environments: metal resistance mechanisms in acidophilic micro-organisms.

Acidophilic micro-organisms inhabit some of the most metal-rich environments known, including both natural and man-made ecosystems, and as such are ideal model systems for study of microbial metal resistance. Although metal resistance systems have been studied in neutrophilic micro-organisms, it is only in recent years that attention has been placed on metal resistance in acidophiles. The five metal resistance mechanisms identified in neutrophiles are also present in acidophiles, in some cases utilizing homologous proteins, but in many cases the degree of resistance is greater in acidophiles. This review summarizes the knowledge of acidophile metal resistance and presents preliminary in silico studies on a few known metal resistance systems in the sequenced acidophile genomes.

VLT observations of metal-rich extra galactic HIIregions

We have obtained high quality FORS1/VLT optical spectra of 85 disk H ii regions in the nearby spiral galaxies NGC 3351, NGC 3521, NGC 4254, NGC 4303, and NGC 4321. Our sample of metal-rich H ii regions with metallicities close to solar and higher reveal the presence of Wolf-Rayet (WR) stars in 27 objects from the blue WR bump (~4680 Å) and 15 additional candidate WR regions. This provides for the first time a large set of metal-rich WR regions. Approximately half (14) of the WR regions also show broad C iv λ5808 emission attributed to WR stars of the WC subtype. The simultaneous detection of C iii λ5696 emission in 8 of them allows us to determine an average late WC subtype compatible with expectations for high metallicities. Combined with literature data, the metallicity trends of WR features and the WC/WN number ratio are discussed. The WR regions show quite clear trends between their observed WR features and the Hβ emission line. Detailed synthesis models are presented to understand/interpret these observations. In contrast with earlier studies of low metallicity WR galaxies, both and are here found to be smaller than “standard” predictions from appropriate evolutionary synthesis models at corresponding metallicities. Various possibilities which could explain this discrepancy are discussed. The most likely solution is found with an improved prescription to predict the line emission from WN stars in synthesis models. The availability of a fairly large sample of metal-rich WR regions allows us to improve existing estimates of the upper mass cut-off of the IMF in a robust way and independently of detailed modeling: from the observed maximum Hβ equivalent width of the WR regions we derive a lower limit for Mup of 60–90 in the case of a Salpeter slope and larger values for steeper IMF slopes. This constitutes a lower limit on Mup as all observational effects known to affect potentially the Hβ equivalent width can only reduce the observed . From our direct probe of the massive star content we conclude that there is at present no evidence for systematic variations of the upper mass cut-off of the IMF in metal-rich environments, in contrast to some claims based on indirect nebular diagnostics.

A dynamical study of the circumstellar gas in UX Orionis

We present the results of a high spectral resolution () study of the circumstellar (CS) gas around the intermediate mass, pre-main sequence star UX Ori. The results are based on a set of 10 échelle spectra covering the spectral range 3800–5900 Å, monitoring the star on time scales of months, days and hours. A large number of transient blueshifted and redshifted absorption features are detected in the Balmer and in many metallic lines. A multigaussian fit is applied to determine for each transient absorption the velocity, v, dispersion velocity, , and the parameter R, which provides a measure of the absorption strength of the CS gas. The time evolution of those parameters is presented and discussed. A comparison of intensity ratios among the transient absorptions suggests a solar-like composition of the CS gas. This confirms previous results and excludes a very metal-rich environment as the cause of the transient features in UX Ori. The features can be grouped by their similar velocities into 24 groups, of which 17 are redshifted and 7 blueshifted. An analysis of the velocity of the groups allows us to identify them as signatures of the dynamical evolution of 7 clumps of gas, of which 4 represent accretion events and 3 outflow events. Most of the events decelerate at a rate of tenths of m s-2, while 2 events accelerate at approximately the same rate; one event is seen experiencing both an acceleration and a deceleration phase and lasts for a period of few days. This time scale seems to be the typical duration of outflowing and infalling events in UX Ori. The dispersion velocity and the relative aborption strength of the features do not show drastic changes during the lifetime of the events, which suggests they are gaseous blobs preserving their geometrical and physical identity. These data are a very useful tool for constraining and validating theoretical models of the chemical and physical conditions of CS gas around young stars; in particular, we suggest that the simultaneous presence of infalling and outflowing gas should be investigated in the context of detailed magnetospheric accretion models, similar to those proposed for the lower mass T Tauri stars.

Abundances in a Hot Horizontal-Branch Star in the Old Open Cluster NGC/6791

The open cluster NGC 6791 is more metal-rich than any other open cluster, yet several hot blue horizontal branch (BHB) stars are probable members. We have performed an abundance analysis of the coolest such star, 2-17, which has a radial velocity and a proper motion which support cluster membership. We find parameters typical of a metal-rich BHB star, with rotational velocity = 16 ± 1 km/s, an effective temperature Teff = 7250 ± 150 K, log gravity = 3.5 ±0.5 dex, and an iron abundance more than twice solar, [Fe/H] = +0.4 ± 0.1 dex. The light even-Z elements Mg, Ca, and Si are further enhanced, ruling out A-star peculiarities. Its analysis thus establishes the cluster metallicity accurately, free from serious blending which is problematical in metal-rich giants. Abundances of C, N, and O suggest little mixing. Visual comparison of the spectra of red HB stars in the cluster with that of the field star μ Leo indicates that the spectra are indistinguishable except for stronger CN in the former.The high iron abundance, the light-element overabundances, the spectral similarity to strong-lined field giants, and the extensive presence of hot stars all highlight the fact that this old open cluster provides an excellent template for the study of metal-rich extragalactic systems. Properties of cluster members should establish not only accurate abundances for comparison with scenarios of nucelosynthesis and star formation, but also provide a testbed for ideas of the production of hot stars in a metal-rich environment, and so for the generation of the ultraviolet upturn in elliptical galaxies.

COMPOSITIONAL TRENDS IN Fe, Co AND Ni SULFARSENIDES AND THEIR CRYSTAL-CHEMICAL IMPLICATIONS: RESULTS FROM THE ARROYO DE LA CUEVA DEPOSITS, RONDA PERIDOTITE, SOUTHERN SPAIN

Fe–Co–Ni sulfarsenides and diarsenides in a pyrrhotite matrix were found as localized segregations in the Arroyo de la Cueva area, at the northwestern margin of the Ronda Peridotite. The pyrrhotite matrix encloses alloclasite, lollingite and pentlandit e, and is cross-cut by veins of chalcopyrite–cubanite intergrowths hosting arsenopyrite, cobaltite and sphalerite, as well as chlorite – magnetite and calcite–talc with minor arsenopyrite and lollingite. Alloclasite, arsenopyrite, cobaltite, lollingite and pentlan dite show strong variation in their contents of Fe, Co, Ni, As and S. Textural and chemical evidence suggests that the ore initially formed at high temperatures and low fugacities of sulfur. The ore was subsequently metasomatized at conditions of gradually increasing sulfur fugacity and decreasing temperatures. The variations in Fe, Co and Ni in alloclasite, cobaltite and pentlandi te describe linear trends. These trends were compared with similar trends from other, especially mafic–ultramafic associations. They depend on both mineral association and the requirement that a structure-specific number of nonbonding metal d electrons be maintained. Three types of trends are shown by the sulfarsenides. 1) Trends describing Co replacement by a mixture of Fe and Ni are shown by sulfarsenides occurring in metal-rich environments. 2) Trends where Co is replaced by Ni occur in associations containing either pyrite, sulfarsenides or diarsenides indicative of higher anion fugacities. 3) Trends shown by sulfarsenides associated with skutterudite describe replacement of Ni by a mixture of Co and Fe. The trends defined by pentlandite compositions indicate the substitution Fe + Ni → 2 Co and support previously suggested bonding models.

Importance of microbial ecology in the development of new mineral technologies

The study of the microbial ecology of extremely acidic, metal-rich environments has provided the foundation from which mineral processing technologies have developed. Many of the microorganisms that are known to have direct or supportive roles in commercial operations were first identified in (and isolated from) environmental samples. Microbial life in this ‘extreme’ environment is now known to be extensively diverse, as new species and genera of acidophiles continue to be discovered. The study of how acidophilic microorganisms interact with each other (a major tenet in microbial ecology) has an important bearing on mineral technologies; microbial consortia rather than single organisms are invariably found in commercial-scale bioleaching operations. Ecologically based studies have also helped to shed new insight into the biogeochemical processes which occur in mineral leaching environments. The application of molecular techniques, particularly when used in conjunction with improved methodologies in more traditional approaches, is providing new insights into environmental and applied aspects of acidophilic microbiology.

Cadmium-regulated gene fusions in Pseudomonas fluorescens.

To study the mechanisms soil bacteria use to cope with elevated concentrations of heavy metals in the environment, a mutagenesis with the lacZ-based reporter gene transposon Tn5B20 was performed. Random gene fusions in the genome of the common soil bacterium Pseudomonas fluorescens strain ATCC 13525 were used to create a bank of 5,000 P. fluorescens mutants. This mutant bank was screened for differential gene expression in the presence of the toxic metal cadmium. Fourteen mutants were identified that responded with increased or reduced gene expression to the presence of cadmium. The mutants were characterized with respect to their metal-dependent gene expression and their metal tolerance. Half the identified mutants reacted with differential gene expression specifically to the metal cadmium, whereas some of the other mutants also responded to elevated concentrations of copper and zinc ions. One of the mutants, strain C8, also showed increased gene expression in the presence of the solvent ethanol, but otherwise no overlap between cadmium-induced gene expression and general stress response was detected. Molecular analysis of the corresponding genetic loci was performed using arbitrary polymerase chain reaction (PCR), DNA sequencing and comparison of the deduced protein products with sequences deposited in genetic databases. Some of the genetic loci targeted by the transposon did not show any similarities to any known genes; thus, they may represent 'novel' loci. The hypothesis that genes that are differentially expressed in the presence of heavy metals play a role in metal tolerance was verified for one of the mutants. This mutant, strain C11, was hypersensitive to cadmium and zinc ions. In mutant C11, the transposon had inserted into a genetic region displaying similarity to genes encoding the sensor/regulator protein pairs of two-component systems that regulate gene expression in metal-resistant bacteria, including czcRS of Ralstonia eutropha, czrRS of Pseudomonas aeruginosa and copRS of Pseudomonas syringae. Although the P. fluorescens strain used in this study had not been isolated from a metal-rich environment, it nevertheless contained at least one genetic region enabling it to cope with elevated concentrations of heavy metals.

Heavy-Element Abundances of the Old Open Cluster NGC 6791

The old open cluster NGC 6791 is believed to be more metal-rich than any other, yet several hot blue horizontal-branch (BHB) stars are probable members. We have performed an abundance analysis of the coolest BHB candidate, 2-17, whose proper motion and radial velocity both support cluster membership. Its luminosity and its low rotational velocity, vsin${r sin}$ -->${r sin}$ -->i=16 ± 1 km s-1, suggest that it is a BHB star rather than a very luminous blue straggler. We find an effective temperature Teff${r eff}$ -->$t SUBgt {r eff}t/SUBgt $ -->=7300 ± 50 K, gravity log${r log}$ -->${r log}$ -->g=3.6 ± 0.3 dex, and an iron abundance more than twice solar, [Fe/H]=+0.4 ± 0.1 dex. This result is free from the serious line blending and continuum suppression that hamper spectroscopic analyses of metal-rich giants. The Ca abundance is in the solar proportion with respect to iron, ruling out A-star peculiarities in 2-17. The relative abundances of C, O, and Al are nearly solar; mixing effects are probably small but not ruled out. The light elements Mg and Si are enhanced, N and Na especially so, as seen in metal-rich galaxies. NGC 6791 thus provides an excellent template for the study of the stellar content of metal-rich galactic systems. Both its abundances and its continued existence suggest that metal-rich systems might generally form in locally deep potential wells. Further study of its hot population should clarify the mechanisms responsible for producing hot stars in a metal-rich environment and thus assist the interpretation of the integrated light and the ultraviolet upturn in elliptical galaxies.

Spectrophotometry of the planetary nebula KjPn 8

Flux-calibrated low-resolution spectra covering the optical wavelength range from 3400 to 7500 A have been obtained over the central region and the surroundings of the extraordinary planetary nebula (PN) KjPn 8 (PNG 112.5-00.1). The spectrum from the core is of low excitation with Te(N II) = 8000 K and ne(S II) = 550 cm−3. KjPn 8 is found to be a Type I PN according to the original classification scheme of Peimbert & Torres-Peimbert, with enriched He/H and N/O ratios with respect to mean values for PN. Increased O/H, Ne/H and Ar/H ratios over those of average PN reflect the possible metal-rich environment from which the progenitor star formed, and also are similar to those found in the extreme Type I PN He 2-111. The N/H ratio is found to be only moderately high compared to the average PN and consequently, the large O abundance pulls the N/O ratio towards the lower limit of the criterion for Type I planetary nebulae (PNe) in this case. In addition, the spectra of some knots and faint regions in the KjPn 8 surroundings are presented, which show only a few spectral lines. Low electron densities ranging from 100 to 300 cm−3 have been derived in these outer regions.

CrSi 2 formation and reduction of Cr 2O 3, during annealing of an oxidized Cr overlayer on Si(111)

A 250 Å thick Cr layer evaporated on Si(111) in ultrahigh-vacuum conditions and subsequently oxidized by exposition to molecular oxygen in order to form a Cr 2O 3 overlayer of ∼10 A ̊ , is studied as a function of annealing in the range 300–800°C by X-ray and ultraviolet photoemission spectroscopy. In the early stages of annealing Si diffusion through the Cr film is observed. These Si atoms are embedded in a metal-rich environment and react readily with the superficial Cr 2O 3 compound to form a film of SiO 2. Upon further annealing it is found that the CrSi 2 growth front reaches the depth probed in our experiments ( ∼ 5–20 A ̊ ). Yet, the results clearly demonstrate that even after prolonged annealing at 500°C complete decomposition of the Cr 2O 3 film does not occur. Apparently, the silicon dioxide already formed acts like a diffusion barrier, preventing further silicon species to reach the remainder of the chromium oxide.

The geological setting of the platinoid and base metal sulfide mineralization in the Platreef of the Bushveld Complex in Drenthe, North of Potgietersrus

On the farm Drenthe, the Platreef consists of a complex assemblage of norites, melanorites, pyroxenites, serpentinites, and xenoliths of dolomite. It is a zone of up to 250 m thick between the basal contact of the complex and the overlying main zone norites. The composition of the orthopyroxene shows a rapid increase from En 60 to En 70 in the lower 30 m of the sequence, and a sharp drop from En 70 to En 60 at the top of the Platreef. This compositional break at the upper contact is due to a change from primary bronzite in the Platreef to inverted pigeonitc in the main zone.High-temperature metamorphic assemblages are preserved in the larger xenoliths, whereas their outer margins and the smaller xenoliths contain retrograde metamorphic mineral assemblages. The igneous rocks display irregularly distributed zones of alteration to bronzite bastitites and serpentinites. The alteration process was probably dominated by degassing of the xenoliths.The distribution and composition of the major sulfide minerals indicate a change from a sulfur-rich to a metal-rich environment during the crystallization of the Platreef. Pyrite, monoclinic pyrrhotite, pentlandite, and chalcopyrite dominate the lower part of the Platreef; and hexagonal pyrrhotite, pentlandite, and chalcopyrite (+ or -cubanite) prevail in the upper portion. Whole-rock analyses show an upward decrease in the Ni/Cu ratio from 1.95 to 1.70. Large variations occur in the distribution and grade of Ni, Cu, and platinum-group elements, although highest values are associated with a zone of serpentinization. The Ni and Cu values are unreliable indicators in predicting Pt and Pd concentrations in zones of major metal enrichment. Ni and Cu correlate strongly while Pt and Pd have more significant correlations with Ni than Cu, although the minerals of the platinum-group elements are primarily associated with chalcopyrite. The Pt/Pd ratio decreases upward in the sequence.The mineralization is considered to have been caused by the breakup of dolomite xenoliths that added CO 2 , H (sub 2>) O, and S to the magma, thus simultaneously lowering the solubility of sulfur in the magma and adding sulfur from an external source, which resulted in the precipitation of an immiscible sulfide liquid.

Overabundances of sodium and the heavy isotopes of magnesium in strong-lined elliptical galaxies

view Abstract Citations (42) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Overabundances of sodium and the heavy isotopes of magnesium in strong-lined elliptical galaxies. Peterson, R. C. Abstract It is shown that overabundances of sodium and the neutron-rich isotopes of magnesium, predicted by calculations of explosive nucleosynthesis in a metal-rich environment, are strongly indicated by a variety of recent observations of strong-lined elliptical galaxies. The theoretical sizes of the overabundances are such as to explain the large increase of the strength of the Na D lines in these objects without invoking sizable numbers of dwarfs, as well as the discrepancies in velocity-dispersion measurements obtained from the characteristic widths of galactic spectral lines by various groups. There is need for an explicit evaluation of the effects of abundance increases on line strengths before the dependence of mass-to-light ratios on galactic luminosity or radial distance may be reliably determined. Publication: The Astrophysical Journal Pub Date: December 1976 DOI: 10.1086/182319 Bibcode: 1976ApJ...210L.123P Keywords: Abundance; Astronomical Spectroscopy; Elliptical Galaxies; Magnesium Isotopes; Sodium; Line Spectra; Luminous Intensity; Nuclear Fusion; Stellar Evolution; Astrophysics full text sources ADS |