Biogenic Origin of Polymetallic Nodules from the Clarion-Clipperton Zone in the Eastern Pacific Ocean: Electron Microscopic and EDX Evidence

Polymetallic/ferromanganese nodules (Mn-nodules) have been assigned a huge economic potential since they contain considerable concentrations of manganese, copper, nickel, iron, and cobalt. It has been assumed that they are formed by, besides hydrogenous, nonbiogenic processes, biogenic processes based on metabolic processes driven by microorganisms. In the present study, we applied the techniques of digital optical microscopy and high-resolution scanning electron microscopy to search for microorganisms in Mn-nodules. They were collected from the Clarion-Clipperton Zone in the Eastern Pacific Ocean and are composed of Mn (23.9%), Cu (0.69%), Ni (1.02%), Fe (10.9%), and Co (0.29%). These Mn-nodules, between 2.3 and 4.8 cm, show a distinct lamination; they are composed of small-sized micronodules, 100 to 450 μm in size, which are bound together by an interstitial whitish material. In the micronodules, a dense accumulation of microorganisms/bacteria could be visualized. Only two morphotypes exist: (1) round-shaped cocci and (2) elongated rods. The cocci (diameter: ≈3.5 μm) are arranged in bead-like chains, while the rods (≈2 × 0.4 μm) are arranged either as palisades or in a linear row. Energy-dispersive X-ray spectroscopy analyses showed that the areas rich in microorganisms/bacteria are also rich in Mn, while in regions where no microorganisms are found, the element Si is dominant. We suggest that growth of the Mn-nodules starts with the formation of “micronodules.” The formation of micronodules is assumed to be mediated by microorganisms. After accretion of biogenic and additional nonbiogenic minerals, the micronodules assemble to large nodules on the sea floor through additional inclusion of nonbiogenic material.     

Dust as a Nutrient Source for Fynbos Ecosystems,South Africa

Abstract Fynbos is the main vegetation of the Cape Floristic Region, a biodiversity hotspot that occurs in southwestern South Africa. A major question concerning the fynbos ecosystem is how it supports abundant and diverse vegetation on soils derived from nutrient-poor bedrock. In addition to marine aerosols (recycled sea salts), geochemical analyses reported here suggest that dust (aeolian) deposition represents a significant source of nutrients (for example, K, Ca and Zn) to the fynbos ecosystem. Headwater portions of the Boontjies River sub-catchment near the Cederberg Mountains support mountain fynbos communities that are entirely underlain by the Peninsula Formation, a quartz arenite with greater than 98 wt% SiO₂. Fynbos soils in these areas are composed of quartzose sand with 3–6 wt% kaolinitic clay and 1–2 wt% organic carbon. The minor amount of feldspar and mica minerals in the bedrock (0.5 wt% Al₂O₃) suggests an aeolian source for much of the clay minerals in the soil. The isotope composition of soluble Pb and Sr from fynbos vegetation and soils indicates a mixture of anthropogenic and terrigenous sources, most likely from washout of combusted petrol and dust from the arid interior particularly in association with Berg Wind events. Approximate mass balance calculations indicate that washout of aerosols provides an important source of nutrients such as Ca, K, P, Fe, Mn and Zn which the fynbos ecosystem is highly effective in retaining.     

Reductive microbial dissolution of manganese nodules as a possible hazard of deep-sea mining

The microbial lysis of deep-sea nodules as a possible result of large-scale, deep-sea mining is considered. It is assumed that the Mn (IV) and Fe (III) compounds of the manganese nodules are reduced by the numerous aerobic bacteria at the sediment/water interface as soon as the adjacent nodule area is buried by sedimentation of the disturbed deposits and the organic-rich debris from the blooming surface plankton. Intensive mineralization processes in the resettled sediments cause oxygen depletion. Subsequently, the aerobic (and anaerobic) microorganisms will switch to Mn (IV) and Fe (III) oxides as alternative electron acceptors in order to continue their energy-conserving (ATP synthesis) reactions (anaerobic respiration). The higher the amount of decomposable organic matter, the more intensive are these processes. Consequently, buried manganese nodules may be dissolved, thereby liberating mobile Mn (II), Fe (II) and several trace elements (Ni, Cu, Co and others). This possible hazard and its ecological consequences should be evaluated carefully before deep-sea mining is started on a large scale.     

Periodic changes in metal content in Fucus distichus thalli under polar day conditions

Variation of Mn, Fe, Ni, Cu and Zn contents in thalli of Fucus distichus was determined under conditions of polar days. The use of spectrum analysis allowed estimates comparisons of the interrelation of periodic changes in irradiance, temperature and tidal fluctuations and quasiperiodic changes in metal contents. The effect of the diel rhythm of irradiance correlated with the accumulation of all metals except for Zn. At the same time, the changes in Mn, Fe and Cu content were delayed in respect to changes in irradiance level. The phase shift for Fe was 1 h 56 min, for Cu – 3 h 41 min and for Mn – 5 h5 min. The change in Ni content, in contrast, was 11min ahead of the change in irradiance. During the experiment an increase in water temperature up to10 °C resulted in increases in the average Mn, Ni and Cu contents in the thalli and decreases in Fe and Zn concents. The periodicity of metal thallus content did not always correspond to a diurnal rhythm, and couldbe longer (Mn, Ni: 32 h; Fe: 36 h) or shorter (Mn, Ni, Zn: 16 h; Cu: 12 h; Zn: 20, 10 h). The ANOVA of these rhythms allows an estimate of the contribution of rising and falling tidal fluctuations to the changes in Cu, Mn and Ni contents. There was a higher metal content during a falling than a rising tide. Abbreviations SDLT – semidiurnal lunartide, CDLT – closed diurnal lunar tide. This revised version was published online in August 2006 with corrections to the Cover Date.     

Trace elements in aerial parts and rhizosphere of <Emphasis Type="Italic">Thymus pannonicus</Emphasis> All.

This paper brings out the results of the study on the levels of selected trace elements (Cu, Fe, Mn, Zn and Cr) in aerial parts of Thymus pannonicus All. (Lamiaceae) and rhizosphere soil from twelve locations in Serbia. Prior to assays by flame and flameless atomic absorption spectrometry, samples were subjected to microwave-assisted acid digestion. Real and potential acidity of soil samples were also measured. Obtained results for soil samples, although slightly higher for some elements (Cu: 12.38–45.18 mg/kg; Fe: 22102–46193 mg/kg; Mn: 776.95–4901.27 mg/kg; Zn: 62.27–214.02 mg/kg; Cr: 48.86–69.13 mg/kg), were found to fit into biogeochemical background. Element contents in plant samples differed depending on collecting site (Cu: 5.26–14.07 mg/kg; Fe: 25.92–1454.07 mg/kg; Mn: 89.29–278.25 mg/kg; Zn: 1.81–10.64 mg/kg; Cr: 1.11–3.51 mg/kg), which can be partly explainable by different nutrient availability influenced by soil acidity. Zinc levels in T. pannonicus were below expected and seem to be strongly influenced by plant physiological properties.     

Mobilization of Minerals to Developing Seeds of Legumes

The mineral nutrition of fruiting plants of Pisum sativum L.,Lupinus albus L. and Lupinus angustifolius L. is examined insand cultures supplying adequate and balanced amounts of essentialnutrients. Changes in content of specific minerals in leaves,pods, seed coat, and embryo are described. P, N and Zn tendto increase precociously in an organ relative to dry matteraccumulation, other elements more or less parallel with (K,Mn, Cu, Mg and Fe) or significantly behind (Ca and Na) dry weightincrease. Some 60–90 per cent of the N, P and K is lostfrom the leaf, pod and seed coat during senescence, versus 20–60per cent of the Mg, Zn, Mn, Fe and Cu and less than 20 per centof the Na and Ca. Mobilization returns from pods are estimatedto provide 4–39 per cent of the seeds' accumulations ofspecific minerals, compared with 4–27 per cent for testatransfer to the embryo. Endosperm minerals are of only minorsignificance in embryo nutrition. Comparisons of the mineral balance of plant parts of Lupinusspp. with that of stem xylem sap and fruit tip phloem sap supportthe view that leaves and pod are principal recipients of xylem-borneminerals and that export from these organs via phloem is themajor source of minerals to the seeds. Endosperm and embryodiffer substantially in mineral compostition from phloem sap,suggesting that selective uptake occurs from the translocationstream during seed development. Considerable differences are observed between species in mineralcomposition of plant organs and in the effectiveness of transferof specific minerals to the seeds Differences between speciesrelate principally to Ca, Na and certain trace elements.     

Bioassay as a tool for assessing susceptible and resistant plant species for field contaminated with industrial effluent

A bioassay technique was used to select plant species that were able to germinate and grow in a site contaminated with flash torch and battery manufacturing industrial effluents. Three varieties each of rice, namely Surya-52, Jaya-14 and Pant-10; three varieties of pulses [Gram (Bahar), Mung (K-851) and Lens (T-9)] and three varieties of oilseeds (Mustard-RS-30, Mustard-B-9 and Mustard T-69) were used for the determination of phytotoxicity by bioassay technique. The average % phytotoxicity for rice was 18.03% (14.34–22.7%), for pulses was 15.76% (8.75–26.64%) and for oil seed was 11.09% (6.42–15.24%). Accumulation of metals (Cu, Fe, Mn, Cd, Cr and Pb) was estimated in the root, shoot and edible parts of different crop varieties grown in pot culture up to maturity and treated with industrial effluent. The concentration of different metal ions in root, shoot and edible parts were in the range of Cu: 9.25–45.25, 7.25–42.35 and 5.65–35.26; Fe: 60.66–212.25, 45.24–155.62; Mn: 7.12–38.30, 6.25–27.27.23 and 4.25–24.45; Cd: 0.80–2.45, 0.75–2.12 and 0.45–1.95, Cr: 6.54–28.25, 5.36–24.45 and 4.35–16.32; and Pb: 0.95–3.75, 0.78–2.25 μg/g d.w. respectively. A higher concentration of Cd was found in Surya-52 rice variety and in Gram (Bahar) pulse variety and of Pb was detected in Surya-52 rice variety. Cd and Pb are non-essential metal ions and highly toxic to plants. Accumulation of toxic metal ions like Pb and Cd in the edible parts of oil a seed variety may not exceed the recommended daily intake limits. Percentage phytotoxicity and inhibition of root and shoot length was also less in the oil seed variety. Thus these plant varieties can be considered for cultivation in fields contaminated by waste from the flash-torch and battery-manufacturing industry.     

Isolation of Mn-SOD and Low Active Fe-SOD from Methylomonas J; Consisting of Identical Proteins

Cultures of Methylomonas J. an aerobic methylotrophic bacterium, were grown both in Mn-rich and Fe-rich media. Crude extracts of the cultures from the Mn-rich and Fe-rich medium showed a specific activity of 12.2 and 0.6 units/mg by a cytochrome c-xanthine oxidase method and 19.4 and 1.3 units/mg by an ESR method, respectively. We isolated Mn-SOD and Fe-SOD from the bacteria grown in the Mn-rich and Fe-rich mediums, respectively. Specific activity and metal contents of the Mn-enzyme were 2,250 units/mg/g-atom Mn and Mn = 0.98 and Fe = 0.12 (g-atoms/mol dirner), while those of the Fe-enzyme were 61 units/mg/g-atom Fe and Mn = 0.02 and Fe = 1.08. No difference of physicochemical properties of the Fe-and Mn-enzymes were detected. Furthermore, enzyme activity was restored by dialysis of an apoprotein obtained from the Fe-enzyme with either manganese sulfate or ferrous ammonium sulfate.     

Stabilization of Soil Organic Matter: Association with Minerals or Chemical Recalcitrance?

Soil organic matter (OM) can be stabilized against decomposition by association with minerals, by its inherent recalcitrance and by occlusion in aggregates. However, the relative contribution of these factors to OM stabilization is yet unknown. We analyzed pool size and isotopic composition (¹⁴C, ¹³C) of mineral-protected and recalcitrant OM in 12 subsurface horizons from 10 acidic forest soils. The results were related to properties of the mineral phase and to OM composition as revealed by CPMAS ¹³C-NMR and CuO oxidation. Stable OM was defined as that material which survived treatment of soils with 6 wt% sodium hypochlorite (NaOCl). Mineral-protected OM was extracted by subsequent dissolution of minerals by 10% hydrofluoric acid (HF). Organic matter resistant against NaOCl and insoluble in HF was considered as recalcitrant OM. Hypochlorite removed primarily ¹⁴C-modern OM. Of the stable organic carbon (OC), amounting to 2.4–20.6 g kg⁻¹ soil, mineral dissolution released on average 73%. Poorly crystalline Fe and Al phases (Fe_o, Al_o) and crystalline Fe oxides (Fe_d−o) explained 86% of the variability of mineral-protected OC. Atomic C_p/(Fe+Al)_p ratios of 1.3–6.5 suggest that a portion of stable OM was associated with polymeric Fe and Al species. Recalcitrant OC (0.4–6.5 g kg⁻¹ soil) contributed on average 27% to stable OC and the amount was not correlated with any mineralogical property. Recalcitrant OC had lower Δ¹⁴C and δ¹³C values than mineral-protected OC and was mainly composed of aliphatic (56%) and O-alkyl (13%) C moieties. Lignin phenols were only present in small amounts in either mineral-protected or recalcitrant OM (mean 4.3 and 0.2 g kg⁻¹ OC). The results confirm that stabilization of OM by interaction with poorly crystalline minerals and polymeric metal species is the most important mechanism for preservation of OM in these acid subsoil horizons.     

Microbial Diversity at a Deep-Sea Station of the Pacific Nodule Province

The Pacific nodule province covers about 4.5 million km² in the eastern tropical Pacific with abundance of polymetallic nodules. Microbes are believed to play large roles in the metal cycling in many environments, but the microbial community in the Pacific nodule province has never been studied. Phylogenetic studies based on 16S rRNA gene sequence analysis, together with bacterial cultivation were used to study the microbial populations in the Pacific nodule province (A core) deep-sea sediment. Bacterial 16S rRNA gene sequence analysisdemonstrated that Proteobacteria division mainly of γ-Proteobacteria dominated the microbial community of the nodule province A core. Among the γ-Proteobacteria, Shewanella species which were known as Fe(□), Mn(□) reducing bacteria were found prevalent. Besides Proteobacteria, Green nonsulfur bacteria, the candidate subdivision OP3, Cytophaga-Flexibacter-Bacteroides bacteria and novel unidentified strains were also detected. Archaeal 16S rDNA sequence analysis data and results from hybridization with crenarchaeotal marine group I specific probe revealed that all archaea detected at the station belong to Crenarchaeota nonthermophilic marinegroup I. Bacteria assigned to the gamma Proteobacteria wereisolated, none of them showed capability of manganese oxidation. These authors contributed equally to this paper.     

The pea ( Pisum sativum L.) genes sym33 and sym40 control infection thread formation and root nodule function

Two novel non-allelic mutants that were unable to fix nitrogen (Fix⁻) were obtained after EMS (ethyl methyl sulfonate) mutagenesis of pea (Pisum sativum L.). Both mutants, SGEFix⁻–1 and SGEFix⁻–2, form two types of nodules: SGEFix⁻–1 forms numerous white and some pink nodules, while mutant SGEFix⁻–2 forms white nodules with a dark pit at the distal end and also some pinkish nodules. Both mutations are monogenic and recessive. In both lines the manifestation of the mutant phenotype is associated with the root genotype. White nodules of SGEFix⁻–1 are characterised by hypertrophied infection threads and infection droplets, mass endocytosis of bacteria, abnormal morphological differentiation of bacteroids, and premature degradation of nodule symbiotic structures. The structure of the pink nodules of SGEFix⁻–1 does not differ from that of the parental line, SGE. White nodules of SGEFix⁻–2 are characterised by “locked” infection threads surrounded with abnormally thick plant cell walls. In these nodules there is no endocytosis of bacteria into host-cell cytoplasm. The pinkish nodules of SGEFix⁻–2 are characterised by virtually undifferentiated bacteroids and premature degradation of nodule tissues. Thus, the novel pea symbiotic genes, sym40 and sym33, identified after complementation analysis in SGEFix⁻–1 and SGEFix⁻–2 lines, respectively, control early nodule developmental stages connected with infection thread formation and function. Received: 12 June 1998 / Accepted: 25 June 1998     

Trace elements in the hydrologic cycle of a forest ecosystem

Summary Concentrations of Cu, Fe, Mn, and Zn were measured in bulk atmospheric precipitation, throughfall, stemflow, and soil solutions at 10−, 15−, 25−, and 30-cm depths, in aEucalyptus globulus forest in the Berkeley hills, California, during the 1974–75 wet season after each main storm event. Litter and plant samples were analyzed. There was some similarity in the behavior of Cu, Fe, and Zn, but Mn behaved differently. Mn and Zn are largely deposited on the forest canopy by impaction during dry-deposition episodes, whereas most of the Cu and Fe input occurs in rain. For the hydrologic components measured, concentrations of Cu and Fe increase in the order: precipitation<throughfall<stemflow <soil solutions. For Zn the order is: precipitation<stemflow<throughfall<soil solutions. Concentrations of Cu, Zn, and Fe in the soil solution fluctuate with downward movement of wetting fronts and are negatively correlated with pH. Concentrations of Fe in soil solution are about 10 times greater than those of throughfall and stemflow; the corresponding relative differences for Cu and Zn were much less. Plant uptake of Mn exceeds that of Cu, Zn, and Fe. The increases in Mn concentrations from precipitation to throughfall and stemflow are much greater than those for Cu, Zn, and Fe because precipitation has very low Mn concentrations. The concentration series for Mn is: precipitation<soil solutions<throughfall<stemflow. Concentrations of Mn in the soil solution are negatively correlated with pH. During the dry summer Mn accumulates in the soil, but is quickly flushed by early rains of the wet season.     

Oxygen cleavage with manganese and iron in ribonucleotide reductase from <Emphasis Type="Italic">Chlamydia trachomatis</Emphasis>

The oxygen cleavage in Chlamydia trachomatis ribonucleotide reductase (RNR) has been studied using B3LYP* hybrid density functional theory. Class Ic C. trachomatis RNR lacks the radical-bearing tyrosine, crucial for activity in conventional class I (subclass a and b) RNR. Instead of the Fe(III)Fe(III)–Tyr(rad) active state, C. trachomatis RNR has a mixed Mn(IV)Fe(III) metal center in subunit II (R2). A mixed MnFe metal center has never been observed as a radical cofactor before. The active state is generated by reductive oxygen cleavage at the metal site. On the basis of calculated barriers for oxygen cleavage in C. trachomatis R2 and R2 from Escherichia coli with a diiron, a mixed manganese–iron, and a dimanganese center, conclusions can be drawn about the effect of changing metals in R2. The oxygen cleavage is found to be governed by two factors: the redox potentials of the metals and the relative stability of the different peroxides. Mn(IV) has higher stability than Fe(IV), and the barrier is therefore lower with a mixed metal center than with a diiron center. With a dimanganese center, an asymmetric peroxide is more stable than the symmetric peroxide, and the barrier therefore becomes too high. Calculated proton-coupled redox potentials are compared to identify three possible R2 active states, the Fe(III)Fe(III)–Tyr(rad) state, the Mn(IV)Fe(III) state, and the Mn(IV)Mn(IV) state. A tentative energy profile of the thermodynamics of the radical transfer from R2 to subunit I is constructed to illustrate how the stability of the active states can be understood from a thermodynamical point of view.     

Effects of iron deficiency and iron overload on manganese uptake and deposition in the brain and other organs of the rat

Managanese (Mn) is an essential trace element at low concentrations, but at higher concentrations is neurotoxic. It has several chemical and biochemical properties similar to iron (Fe), and there is evidence of metabolic interaction between the two metals, particularly at the level of absorption from the intestine. The aim of this investigation was to determine whether Mn and Fe interact during the processes involved in uptake from the plasma by the brain and other organs of the rat. Dams were fed control (70 mg Fe/kg), Fe-deficient (5–10 mg Fe/kg), or Fe-loaded (20 g carbonyl Fe/kg) diets, with or without Mn-loaded drinking water (2 g Mn/L), from day 18–19 of pregnancy, and, after weaning the young rats, were continued on the same dietary regimens. Measurements of brain, liver, and kidney Mn and nonheme Fe levels, and the uptake of⁵⁴Mn and⁵⁹Fe from the plasma by these organs and the femurs, were made when the rats were aged 15 and 63 d. Organ nonheme Fe levels were much higher than Mn levels, and in the liver and kidney increased much more with Fe loading than did Mn levels with Mn loading. However, in the brain the increases were greater for Mn. Both Fe depletion and loading led to increased brain Mn concentrations in the 15-d/rats, while Fe loading also had this effect at 63 d. Mn loading did not have significant effects on the nonheme Fe concentrations.⁵⁴Mn, injected as MnCl₂ mixed with serum, was cleared more rapidly from the circulation than was⁵⁹Fe, injected in the form of diferric transferrin. In the 15-d-rats, the uptake of⁵⁴Mn by brain, liver, kidneys, and femurs was increased by Fe loading, but this was not seen in the 63-d rats. Mn supplementation led to increased⁵⁹Fe uptake by the brain, liver, and kidneys of the rats fed the control and Fe-deficient diets, but not in the Fe-loaded rats. It is concluded that Mn and Fe interact during transfer from the plasma to the brain and other organs and that this interaction is synergistic rather than competitive in nature. Hence, excessive intake of Fe plus Mn may accentuate the risk of tissue damage caused by one metal alone, particularly in the brain.     

Dissimilatory Reduction of Fe(III) by Thermophilic Bacteria and Archaea in Deep Subsurface Petroleum Reservoirs of Western Siberia

Twenty-five samples of stratal fluids obtained from a high-temperature (60–84°C) deep subsurface (1700–2500 m) petroleum reservoir of Western Siberia were investigated for the presence of dissimilatory Fe(III)-reducing microorganisms. Of the samples, 44% and 76% were positive for Fe(III) reduction with peptone and H₂ respectively as electron donors. In most of these samples, the numbers of culturable thermophilic H₂-utilizing iron reducers were in the order of 10–100 cells/ml. Nine strains of thermophilic anaerobic bacteria and archaea isolated from petroleum reservoirs were tested for their ability to reduce Fe(III). Eight strains belonging to the genera Thermoanaerobacter, Thermotoga, and Thermococcus were found capable of dissimilatory Fe(III) reduction, with peptone or H₂ as electron donor and amorphous Fe(III) oxide as electron acceptor. These results demonstrated that Fe(III) reduction may be a common feature shared by a wide range of anaerobic thermophiles and hyperthermophiles in deep subsurface petroleum reservoirs. Received: 1 March 1999 / Accepted: 5 April 1999     

Characterization of natural variation for zinc, iron and manganese accumulation and zinc exposure response in Brassica rapa L.

Brassica rapa L. is an important vegetable crop in eastern Asia. The objective of this study was to investigate the genetic variation in leaf Zn, Fe and Mn accumulation, Zn toxicity tolerance and Zn efficiency in B. rapa. In total 188 accessions were screened for their Zn-related characteristics in hydroponic culture. In experiment 1, mineral assays on 111 accessions grown under sufficient Zn supply (2 μM ZnSO₄) revealed a variation range of 23.2–155.9 μg g⁻¹ dry weight (d. wt.) for Zn, 60.3–350.1 μg g⁻¹ d. wt. for Fe and 20.9–53.3 μg g⁻¹ d. wt. for the Mn concentration in shoot. The investigation of tolerance to excessive Zn (800 μM ZnSO₄) on 158 accessions, by using visual toxicity symptom parameters (TSPs), identified different levels of tolerance in B. rapa. In experiment 2, a selected sub-set of accessions from experiment 1 was characterized in more detail for their mineral accumulation and tolerance to excessive Zn supply (100 μM and 300 μM ZnSO₄). In this experiment Zn tolerance (ZT) determined by relative root or shoot dry biomass varied about 2-fold. The same six accessions were also examined for Zn efficiency, determined as relative growth under 0 μM ZnSO₄ compared to 2 μM ZnSO₄. Zn efficiency varied 1.8-fold based on shoot dry biomass and 2.6-fold variation based on root dry biomass. Zn accumulation was strongly correlated with Mn and Fe accumulation both under sufficient and deficient Zn supply. In conclusion, there is substantial variation for Zn accumulation, Zn toxicity tolerance and Zn efficiency in Brassica rapa L., which would allow selective breeding for these traits.     

Leaching of silica and uranium and other quantitative aspects of the lithobiontic colonization in a radioactive thermal spring

The formation of microbial mats by thermophilic organisms on submerged rocks in radioactive thermal springs was followed quantitatively in situ as well as under experimental conditions, by determining the change in dry weight and organic matter as a function of time. Furthermore, the decay of the rock occurring in the springs could be shown to be directly related to the microbial colonization. Early in that process the formation of silicious gels, facilitating the settling of the organisms, could be observed. Simultaneously, this was accompanied by the leaching of silica from the underlying rock. This resulted in the destruction of the rock, which had been altered to a fine-grained dust underneath the colonizing mats; the microorganisms were found to move further downward within this layer. From the heavy metals present in the rock—iron (Fe), copper (Cu), manganese (Mn), uranium (U)— the leaching of uranium could be demonstrated, leading to the acquisition of this metal in the microbial mats in concentrations up to 15.34g/mg dry weight. Direct evidence for the leaching of Si (silicon) and U could be obtained by measurement of these elements after their release from ground rock chips in cultures with microorganisms from the hot springs at 50°C. X-ray analysis of the biomats strongly suggested that Cu, Mn, and Fe are also accumulated.     

Reduction of Fe(III), Mn(IV), and Toxic Metals at 100°C by Pyrobaculum islandicum

It has recently been noted that a diversity of hyperthermophilic microorganisms have the ability to reduce Fe(III) with hydrogen as the electron donor, but the reduction of Fe(III) or other metals by these organisms has not been previously examined in detail. When Pyrobaculum islandicum was grown at 100°C in a medium with hydrogen as the electron donor and Fe(III)-citrate as the electron acceptor, the increase in cell numbers of P. islandicum per mole of Fe(III) reduced was found to be ca. 10-fold higher than previously reported. Poorly crystalline Fe(III) oxide could also serve as the electron acceptor for growth on hydrogen. The stoichiometry of hydrogen uptake and Fe(III) oxide reduction was consistent with the oxidation of 1 mol of hydrogen resulting in the reduction of 2 mol of Fe(III). The poorly crystalline Fe(III) oxide was reduced to extracellular magnetite. P. islandicum could not effectively reduce the crystalline Fe(III) oxide minerals goethite and hematite. In addition to using hydrogen as an electron donor for Fe(III) reduction, P. islandicum grew via Fe(III) reduction in media in which peptone and yeast extract served as potential electron donors. The closely related species P. aerophilum grew via Fe(III) reduction in a similar complex medium. Cell suspensions of P. islandicum reduced the following metals with hydrogen as the electron donor: U(VI), Tc(VII), Cr(VI), Co(III), and Mn(IV). The reduction of these metals was dependent upon the presence of cells and hydrogen. The metalloids arsenate and selenate were not reduced. U(VI) was reduced to the insoluble U(IV) mineral uraninite, which was extracellular. Tc(VII) was reduced to insoluble Tc(IV) or Tc(V). Cr(VI) was reduced to the less toxic, less soluble Cr(III). Co(III) was reduced to Co(II). Mn(IV) was reduced to Mn(II) with the formation of manganese carbonate. These results demonstrate that biological reduction may contribute to the speciation of metals in hydrothermal environments and could account for such phenomena as magnetite accumulation and the formation of uranium deposits at ca. 100°C. Reduction of toxic metals with hyperthermophilic microorganisms or their enzymes might be applied to the remediation of metal-contaminated waters or waste streams.     

The reserve of weatherable primary silicates impacts the accumulation of biogenic silicon in volcanic ash soils

Banana plantlets (Musa acuminata cv Grande Naine) cultivated in hydroponics take up silicon proportionally to the concentration of Si in the nutrient solution (0–1.66 mM Si). Here we study the Si status of banana plantlets grown under controlled greenhouse conditions on five soils developed from andesitic volcanic ash, but differing in weathering stage. The mineralogical composition of soils was inferred from X-ray diffraction, elemental analysis and selective chemical/mineralogical extractions. With increasing weathering, the content of weatherable primary minerals decreased. Conversely, clay content increased and stable secondary minerals were increasingly dominant: gibbsite, Fe oxides, allophane, halloysite and kaolinite. The contents of biogenic Si in plant and soil were governed by the reserve of weatherable primary minerals. The largest concentrations of biogenic Si in plant (6.9–7 g kg⁻¹) and soil (50–58 g kg⁻¹) occurred in the least weathered soils, where total Si content was above 225 g kg⁻¹. The lowest contents of biogenic Si in plant (2.8–4.3 g kg⁻¹) and soil (8–31 g kg⁻¹) occurred in the most weathered desilicated soils enriched with secondary oxides and clay minerals. Our data imply that soil weathering stage directly impacted the soil-to-plant transfer of silicon, and thereby the stock of biogenic Si in a soil–plant system involving a Si-accumulating plant. They further imply that soil type can influence the silicon soil–plant cycle and its hydrological output.     

The Effects of FeCl<Subscript>3</Subscript> and Fe–EDTA on the Development of Psoriasis

The effects of FeCl₃ and Fe–EDTA on the development of psoriasis were studied in the mouse model of vaginal epithelium and tail epidermis. The mitoses of vaginal epithelial cell in female mice of their estrogenic stage and the formation of granular cell layers in male mouse tail scale were observed. Mice were randomly divided into eight groups and treated with normal saline, methotrexate, and different doses of two iron forms, FeCl₃ and Fe–EDTA, respectively, for 10 days. To explore the influence of FeCl₃ and Fe–EDTA on the excretion of Cu, Fe, Zn, Ca, Mg, Mn, and Se, the concentration of those elements in liver and kidney was analyzed by atomic absorption spectrometry. The different doses of FeCl₃ or Fe–EDTA could obviously inhibit the mitoses of vaginal epithelial cell (p< 0.05) and promote the formation of granular cell layers in mice tail scale (p < 0.05). No statistically significant results were found between the groups of FeCl₃ and Fe–EDTA, and between experimental groups and methotrexate group acted as the positive control (p>0.05). Compared with the negative group, the concentrations of Cu, Fe, Zn, Ca, Mg, Mn, and Se in liver and kidney of experimental groups and positive control group were not significantly changed (p > 0.05). FeCl₃ and Fe–EDTA are as effective as methotrexate on inhibiting hyperplasia of epidermal cells and increasing the formation of granular cell layers, and the concentrations of Cu, Fe, Zn, Ca, Mg, Mn, and Se in liver and kidney of experimental groups and positive control group were not significantly changed compared with the negative group, possibly retarding the development of psoriasis.