Biosorption of tungstate by a Bacillus sp. isolated from Anzali lagoon

An attempt was made to isolate bacterial strains capable of biologically removing tungstate (WO₄²⁻). Thirty-eight water samples were collected from various areas of Anzali lagoon, Iran. Initial screening of a total of 100 bacterial isolates at pH 5, resulted in the selection of one isolate with maximum adsorption capacity of 65.4 mg tungstate/g dry weight. It was tentatively identified as Bacillus sp. according to morphological and biochemical properties and named strain MGG-83. Tungsten concentration was measured spectrophotometrically using the dithiol method. Higher adsorption capacity was observed in the acidic pH ranging from 1 to 3. At pH 2, the strain removed 274.4 mg tungstate/g dry weight within 5 min from the solution with 300 mg WO₄²⁻/l initial concentration and thereafter adsorption rate decreased remarkably. The applicability of the Freundlich isotherm for representation of the experimental data was investigated. Using 1 mM sodium azide and 10 mM 2,4−dinitrophenol, it was shown that only 20% reduction occurred in adsorption and steam sterilization of the bacterial cells resulted in 11% decrease in tungstate uptake. Temperature variations (20–40°C) had no significant effect on tungstate uptake. Pretreatment with the cations had no effect in uptake but pretreatment with anions decreased the tungstate uptake as indicated: sulfate > chromate > nitrate > molybdate > selenate > rhenate. Tungstate was removed from metal-laden biomass after desorption treatments by addition of different desorbing solutions with the results sodium acetate > EDTA > NaCl > KOH > H₂SO₄.     

Adsorption of reovirus to clay minerals: effects of cation-exchange capacity, cation saturation, and surface area.

The adsorption of reovirus to clay minerals has been reported by several investigators, but the mechanisms defining this association have been studied only minimally. The purpose of this investigation was to elucidate the mechanisms involved with this interaction. More reovirus type 3 was adsorbed, in both distilled and synthetic estuarine water, by low concentrations of montmorillonite than by comparable concentrations of kaolinite containing a mixed complement of cations on the exchange complex. Adsorption to the clays was essentially immediate and was correlated with the cation-exchange capacity of the clays, indicating that adsorption was primarily to negatively charged sites on the clays. Adsorption was greater with low concentrations of clays in estuarine water than in distilled water, as the higher ionic strength of the estuarine water reduced the electrokinetic potential of both clay and virus particles. The addition of cations (as chloride salts) to distilled water enhanced adsorption, with divalent cations being more effective than monovalent cations and 10(-2) M resulting in more adsorption than 10(-3) M. Potassium ions suppressed reovirus adsorption to montmorillonite, probably by collapsing the clay lattices and preventing the expression of the interlayer-derived cation-exchange capacity. More virus was adsorbed by montmorillonite made homoionic to various mono-, di-, and trivalent cations (except by montmorillonite homoionic to potassium) than by comparable concentrations of kaolinite homoionic to the same cations. The sequence of the amount of adsorption to homoionic montmorillonite was Al greater than Ca greater than Mg greater than Na greater than K; the sequence of adsorption to kaolinite was Na greater than Al greater than Ca greater than Mg greater than K. The constant partition-type adsorption isotherms obtained when the clay concentration was maintained constant and the virus concentration was varied indicated that a fixed proportion of the added virus population was adsorbed, regardless of the concentration of infectious particles. A heterogeneity within the reovirus population was indicated.     

Adsorption and anti-ultraviolet light characteristics of the protoxin from Bacillus thuringiensis on montmorillonite,kaolinite, zinc oxide and rectorite

The adsorption, desorption and anti-ultraviolet light characteristics of the protoxin from Bacillus thuringiensis strain WG-001 on montmorillonite, kaolinite, zinc oxide and rectorite were studied. The protoxin was easily adsorbed onto minerals and the adsorption reached equilibrium within 0.5–1.0 h (except for rectorite). The adsorption isotherms of protoxin at different concentrations in sodium carbonate buffer (pH 9) followed the Langmuir (R ² >0.97) and Freundlich (R ² >0.95) equations. The maximum amounts of protoxin adsorbed were in the order: montmorillonite>rectorite>znic oxide>kaolinite. In the range of pH from 9 to 11 (carbonate buffer), the protoxin adsorbed decreased with increasing pH. The adsorption was not significantly affected by the temperature between 5 and 45°C. Both free and adsorbed protoxin were toxic to larvae of Heliothis armigera. The LC₅₀ value of free and adsorbed protoxin on montmorillonite, rectorite, zinc oxide and kaolinite were 14±1.16, 1.76±0.31, 2.94±0.71, 4.78±2.08 and 1.91±0.91 µg mL^?1, respectively. After 1 h of ultraviolet irradiation, the LC₅₀ of the above samples increased by 41.4, 19.3, 16.3, 125.9 and 62.3%, respectively. The desorption of adsorbed protoxin in water ranged from 30.1 to 64.9% and from 18.5 to 48.7% in carbonate buffer.     

Transformation of clay minerals caused by an alkaliphilic cyanobacterial community

Transformation of clay minerals (smectite-zeolite, illite, kaolinite, and bentonite) and admixtures of iron oxides (hydroxides) under the action of an alkaline cyanobacterial community was studied. The results demonstrate that the processes of transformation of clay minerals such as intensification of removal of exchange bases and dissolution of silicates and iron oxides occurred in the presence of the alkaliphilic cyanobacterial community. The main factor that determines resistance of a mineral to biochemical weathering is its composition. Transformations of clay minerals in the course of active cyanobacterial photosynthesis (up to 14 days) and at decomposition of organic matter (OM) (28–60 days) are different. For smectite-zeolite and illite, these processes are dissolution of silicates and oxides (removal of Si and Fe) and removal of exchange bases (K), which were observed at both the of biomass production and OM destruction stages. For two other clays, the processes of neosynthesis are more typical: formation of carbonates (most probably siderite for bentonite clay and Mg-calcite for kaolin clay) and transformation of ferrihydrite into the more thermodynamically stable goethite.     

The tungsten metallome of Pyrococcus furiosus

The tungsten metallome of the hyperthermophilic archaeon Pyrococcus furiosus has been investigated using electroanalytical metal analysis and native-native 2D-PAGE with the radioactive tungsten isotope (187)W (t(1/2) = 23.9 h). P. furiosus cells have an intracellular tungsten concentration of 29 μM, of which ca. 30% appears to be free tungsten, probably in the form of tungstate or polytungstates. The remaining 70% is bound by five different tungsten enzymes: formaldehyde ferredoxin oxidoreductase, aldehyde ferredoxin oxidoreductase, glyceraldehyde-3-phosphate ferredoxin oxidoreductase and the tungsten-containing oxidoreductases WOR4 and WOR5. The membrane proteome of P. furiosus is devoid of tungsten. The differential expression, as measured by the tungsten level, of the five soluble tungsten enzymes when the cells are subjected to a cold-shock shows a strong correlation with previously published DNA microarray analyses.     

Adsorption/Desorption of toluene on clay minerals

Adsorption/desorption of toluene on montmorillonite, illite, and kaolinite was studied using the batch equilibrium method. The isotherms measured fit the Freundlich equation (r² >0.95). Montmorillonite adsorbed more toluene than illite or kaolinite; the adsorption of toluene on illite and kaolinite was not significantly different. Adsorption of toluene by montmorillonite showed an exponential increase as the ratio of toluene to clay was increased from 5 to 100. The rate studies showed that 62% of the adsorption was completed within 6 h. A rapid desorption was observed initially, followed by slow desorption after 1 h. The desorption rate decreased as the time of adsorption was increased. Almost all of the adsorbed toluene was extracted with water from the clay when the adsorption time was 0.1 h, but only 61% of the toluene could be desorbed when the adsorption time was 24 h.     

Adsorption of Adenine, Cytosine, Thymine, and Uracil on Sulfide-Modified Montmorillonite: FT-IR, M?ssbauer and EPR Spectroscopy and X-Ray Diffractometry Studies

In the present work the interactions of nucleic acid bases with and adsorption on clays were studied at two pHs (2.00, 7.00) using different techniques. As shown by Mössbauer and EPR spectroscopies and X-ray diffractometry, the most important finding of this work is that nucleic acid bases penetrate into the interlayer of the clays and oxidize Fe²⁺ to Fe³⁺, thus, this interaction cannot be regarded as a simple physical adsorption. For the two pHs the order of the adsorption of nucleic acid bases on the clays was: adenine????cytosine?>?thymine?>?uracil. The adsorption of adenine and cytosine on clays increased with decreasing of the pH. For unaltered montmorillonite this result could be explained by electrostatic forces between adenine/cytosine positively charged and clay negatively charged. However for montmorillonite modified with Na₂S, probably van der Waals forces also play an important role since both adenine/cytosine and clay were positively charged. FT-IR spectra showed that the interaction between nucleic acid bases and clays was through NH⁺ or NH ₂ ⁺ groups. X-ray diffractograms showed that nucleic acid bases adsorbed on clays were distributed into the interlayer surface, edge sites and external surface functional groups (aluminol, silanol) EPR spectra showed that the intensity of the line g????2 increased probably because the oxidation of Fe²⁺ to Fe³⁺ by nucleic acid bases and intensity of the line g?=?4.1 increased due to the interaction of Fe³⁺ with nucleic acid bases. Mössbauer spectra showed a large decreased on the Fe²⁺ doublet area of the clays due to the reaction of nucleic acid bases with Fe²⁺.     

Distorted octahedral coordination of tungstate in a subfamily of specific binding proteins

Bacteria and archaea import molybdenum and tungsten from the environment in the form of the oxyanions molybdate (MoO₄ ²⁻) and tungstate (WO₄ ²⁻). These substrates are captured by an external, high-affinity binding protein, and delivered to ATP binding cassette transporters, which move them across the cell membrane. We have recently reported a crystal structure of the molybdate/tungstate binding protein ModA/WtpA from Archaeoglobus fulgidus, which revealed an octahedrally coordinated central metal atom. By contrast, the previously determined structures of three bacterial homologs showed tetracoordinate molybdenum and tungsten atoms in their binding pockets. Until then, coordination numbers above four had only been found for molybdenum/tungsten in metalloenzymes where these metal atoms are part of the catalytic cofactors and coordinated by mostly non-oxygen ligands. We now report a high-resolution structure of A. fulgidus ModA/WtpA, as well as crystal structures of four additional homologs, all bound to tungstate. These crystal structures match X-ray absorption spectroscopy measurements from soluble, tungstate-bound protein, and reveal the details of the distorted octahedral coordination. Our results demonstrate that the distorted octahedral geometry is not an exclusive feature of the A. fulgidus protein, and suggest distinct binding modes of the binding proteins from archaea and bacteria. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. K. Hollenstein and M. Comellas-Bigler contributed equally to this work.     

Dynamic role of “illite-like” clay minerals in temperate soils: facts and hypotheses

Analysis of new data and reinterpretation of published information for clay minerals found in temperate climate soil profiles indicates that there is often a gradient of “illite-like” clay minerals with depth. We used the term “illite-like” because these observations are based on X-Ray Diffractogram patterns and not on layer charge measurements which allow to define properly illite. It appears that “illite-like” layers are concentrated in the upper, organic - rich portion of the soil profile both under grassland and forest vegetation. “Illite-like” layer quantity seems directly related to soil potassium status. Indeed, intensive agriculture practises without potassium fertilization reduce “illite-like” content in surface soils, whereas several years of potassic fertilization without plant growth can increase “illite-like” content. The potassic soil clay mineral, illite, is particularly important in that it can be the major source of readily available potassium for plants. Spatial and temporal dynamics of clay minerals should be related to the potassium cycle. We propose that the frequently observed general trend of increasing exchangeable potassium in the top soil can be correlated with an increase in “illite-like” in the clays and that the decrease of potassium caused by intensive agricultural practices leads to “illite-like” layer destabilization. This vision of “illite-like” layer as a potassium reservoir refueled by plants and emptied by intensive cropping renews the concept of potassium availability and indicates a need to be discussed as well in natural ecosystems as in cultivated ecosystems.     

Clay Mineralogy of Central Victorian (Creswick) Soils: Clay Mineral Contents as a Possible Tool of Environmental Indicator

The clay mineralogy and heavy metal/metalloid (As, Pb and Cu) contents of soils developed on the various rock units in a central highlands environment in Victoria (Creswick, Australia) have been investigated. The clay minerals identified showed an order of abundance as: kaolinite ? illite > smectite > mixed-layer (ML) ≈ vermiculite. The soil clay mineralogy did not change systematically with depth (0～ 10, 10～ 20 and 20～ 30 cm) and showed large variations spatially. The high proportion of kaolinite was probably due to the removal of 2:1 phyllosilicates by the formation of 1:1 kaolinite through weathering, which also reduced the cation exchange capacity (CEC) and electrical conductivity (EC, soil: water ratio of 1:5) of soils by aging. Soils were classified as silty loam to loam with a low clay size (≤ 2μ m) fraction. The soils were acidic to moderately acidic with pH ranging from 4.5 to 7.1, averaging 5.7. Concentrations of As, Pb, and Cu (average values 24.3, 16.7 and 11.0 mg/kg, respectively) did not show an association with the clay mineral contents except vermiculite. The occurrence of smectite and mixed-layer clay contents, although far lower than kaolinite and illite, contributed significantly to CEC of soils. The study area was affected by mining, high natural background As values dominate the area and the role of clay minerals in fixation of metalloid/metals was found to be less significant. Low organic matter content (average ～ 6.5%), low soil surface area (average ～ 1.0 m²/g) and the high proportion of kaolinite mineral content result in a limited ability to fix heavy metals. The role of Fe oxides appeared to be a key influence in the fixation of As and other potentially toxic metals, rather than the clay minerals, and therefore requires further research. This work highlighted the importance of the determination of types and amounts of clay minerals of natural soils in environmental management.     

Short-term effects of biological and physical forces on aggregate formation in soils with different clay mineralogy

The mechanisms resulting in the binding of primary soil particles into stable aggregates vary with soil parent material, climate, vegetation, and management practices. In this study, we investigated short-term effects of: (i) nutrient addition (Hoagland's solution), (ii) organic carbon (OC) input (wheat residue), (iii) drying and wetting action, and (iv) root growth, with or without dry–wet cycles, on aggregate formation and stabilization in three soils differing in weathering status and clay mineralogy. These soils included a young, slightly weathered temperate soil dominated by 2:1 (illite and chlorite) clay minerals; a moderately weathered soil with mixed [2:1 (vermiculite) and 1:1 (kaolinite)] clay mineralogy and oxides; and a highly weathered tropical soil dominated by 1:1 (kaolinite) clay minerals and oxides. Air-dried soil was dry sieved through a 250 m sieve to break up all macroaggregates and 100 g-subsamples were brought to field capacity and incubated for 42 days. After 14 and 42 days, aggregate stability was measured on field moist and air-dried soil, to determine unstable and stable aggregation respectively. In control treatments (i.e., without nutrient or organic matter addition, without roots and at constant moisture), the formation of unstable and stable macroaggregates (> 250 m) increased in the order: 2:1 clay soil < mixed clay soil < 1:1 clay soil. After 42 days of incubation, nutrient addition significantly increased both unstable and stable macroaggregates in the 2:1 and 1:1 clay soils. In all soils, additional OC input increased both unstable and stable macroaggregate formation. The increase in macroaggregation with OC input was highest for the mixed clay soil and lowest for the 1:1 clay soil. In general, drying and wetting cycles had a positive effect on the formation of macroaggregates. Root growth caused a decrease in unstable macroaggregates in all soils. Larger amounts of macroaggregates were found in the mixed clay and oxides soil when plants were grown under 50% compared to 100% field capacity conditions. We concluded that soils dominated by variable charge clay minerals (1:1 clays and oxides) have higher potential to form stable aggregates when OC concentrations are low. With additional OC inputs, the greatest response in stable macroaggregate formation occurred in soils with mixed mineralogy, which is probably a result of different binding mechanisms occurring: i.e., electrostatic bindings between 2:1 clays, 1:1 clays and oxides (i.e. mineral-mineral bindings), in addition to OM functioning as a binding agent between 2:1 and 1:1 clays.     

Impact of Clay Minerals on Sulfate-Reducing Activity in Aquifers

Previous studies have shown that sulfate-reduction activity occurs in a heterogeneous manner throughout the terrestrial subsurface. Low-activity regions are often observed in the presence of clay minerals. Here we report that clays inhibit sulfate reduction activity in sediments and in a pure culture of Desulfovibrio vulgaris. Clay minerals including bentonite and kaolinite inhibited sulfate reduction by 70–90% in sediments. Intact clays and clay colloids or soluble components, capable of passing through a 0.2-µm filter, were also inhibitory to sulfate-reducing bacteria. Other adsorbent materials, including anion or cation exchangers and a zeolite, did not inhibit sulfate reduction in sediments, suggesting that the effect of clays was not due to their cation-exchange capacity. We observed a strong correlation between the Al₂O₃ content of clays and their relative ability to inhibit sulfate reduction in sediments (r² = 0.82). This suggested that inhibition might be a direct effect of Al³⁺ (aq) on the bacteria. We then tested pure aluminum oxide (Al₂O₃) and showed it to act in a similar manner to clay. As dissolved aluminum is known to be toxic to a variety of organisms at low concentrations, our results suggest that the effects of clay on sulfate-reducing bacteria may be directly due to aluminum. Thus, our experiments provide an explanation for the lack of sulfate-reduction activity in clay-rich regions and presents a mechanism for the effect.     

Microbial reduction of structural iron in interstratified illite-smectite minerals by a sulfate-reducing bacterium

Clay minerals are ubiquitous in soils, sediments, and sedimentary rocks and could coexist with sulfate‐reducing bacteria (SRB) in anoxic environments, however, the interactions of clay minerals and SRB are not well understood. The objective of this study was to understand the reduction rate and capacity of structural Fe(III) in dioctahedral clay minerals by a mesophilic SRB, Desulfovibrio vulgaris and the potential role in catalyzing smectite illitization. Bioreduction experiments were performed in batch systems, where four different clay minerals (nontronite NAu‐2, mixed‐layer illite‐smectite RAr‐1 and ISCz‐1, and illite IMt‐1) were exposed to D. vulgaris in a non‐growth medium with and without anthraquinone‐2,6‐disulfonate (AQDS) and sulfate. Our results demonstrated that D. vulgaris was able to reduce structural Fe(III) in these clay minerals, and AQDS enhanced the reduction rate and extent. In the presence of AQDS, sulfate had little effect on Fe(III) bioreduction. In the absence of AQDS, sulfate increased the reduction rate and capacity, suggesting that sulfide produced during sulfate reduction reacted with the phyllosilicate Fe(III). The extent of bioreduction of structural Fe(III) in the clay minerals was positively correlated with the percentage of smectite and mineral surface area of these minerals. X‐ray diffraction, and scanning and transmission electron microscopy results confirmed formation of illite after bioreduction. These data collectively showed that D. vulgaris could promote smectite illitization through reduction of structural Fe(III) in clay minerals.     

Effect of biotite,zeolite, heavy clay,bentonite and apatite on the uptake of radiocesium by grass from peat soil

Biotite is a potassium rich mineral, which is used as a fertilizer in organic farming and as a soil amendment in conventional farming. Its ability to reduce ¹³⁴Cs uptake by ryegrass from peat soil was studied in pot experiments and compared with zeolite, heavy clay, bentonite and apatite. In addition, the long-term effect of biotite on ¹³⁷Cs uptake from peat soil was studied in the peat field. In the pot experiments in the first cut of ryegrass, the minerals decreased ¹³⁴Cs uptake by plants in the following order: zeolite > heavy clay > bentonite > biotite > apatite. Apatite did not have any effect on the plant ¹³⁴Cs level. In the later cuts, the uptake of ¹³⁴Cs from biotite-treated soil decreased further while that from soils treated with other minerals remained unchanged or even increased. In general, ¹³⁴Cs uptake by plants decreased with increasing mineral level. The decrease of ¹³⁴Cs uptake became more efficient, especially at the early growth stage, by mixing small amounts of zeolite in biotite. The results of the field experiment indicated the long-term effect of biotite on reducing ¹³⁴Cs uptake by plants. Biotite application rate was 30 t ha-1. The five-year mean of the plant/soil concentration ratio of ¹³⁷Cs was 0.05 for biotite-treated soil, in contrast to 0.14 for the control soil. On the whole, biotite reduced considerably the ¹³⁷Cs level of plants on peat soil and this effect was long-lasting. For an effective reduction of plant radiocesium a great quantity of biotite is needed and therefore it is most suitable for greenhouse cultivation where contaminated slightly decomposed peat is used as a growing medium.     

Shewanella putrefaciens CN32对粘土附着态铵氮释放的影响

【目的】研究产胞外分泌物微生物Shewanella putrefaciens CN32对土壤中常见粘土矿物附着态NH_4~+的释放效果及影响机制。【方法】以吸附NH_4~+的蒙脱石、蛭石、伊蒙混层矿物和黑云母为对象,通过监测S. putrefaciens CN32作用下不同粘土释放的NH_4~+含量及过程,以及监测微生物量及释放的胞外聚合物(Extracellular Polymeric Substances,EPS)的含量变化,研究S. putrefaciens CN32作用下不同粘土矿物类型附着态NH_4~+释放的差异性。【结果】粘土矿物附着态NH_4~+含量从高到低依次为蒙脱石蛭石伊蒙混层矿物黑云母(黑云母NH_4~+吸附量极低,会在非生物作用下几乎完全释放),CN32作用下粘土附着态NH_4~+相对释放量依次为蒙脱石伊蒙混层矿物蛭石;然而,尽管CN32有效促进了粘土附着态NH_4~+释放,但释放的NH_4~+并未在溶液中大量累积,而是多被微生物同化吸收转化为生物有机氮(EPS为主)并吸附在粘土表面,且粘土对EPS的吸附能力表现为蒙脱石伊蒙混层矿物蛭石黑云母;由于粘土吸附NH_4~+及EPS都与矿物中的羟基(结构水或层间水)关系密切,推测EPS对矿物羟基的竞争吸附可能是CN32促进NH_4~+释放的重要原因之一。【结论】以上结果表明,产EPS微生物S. putrefaciens CN32能够促进各类粘土矿物的附着态NH_4~+释放,但释放的NH_4~+可以通过微生物作用转化为有机氮,从而在减少NH_4~+流失的同时增加土壤氮肥的生物可利用性,因此微生物在降低土壤氮肥流失、转化土壤氮肥污染过程中可能起到了重要作用,也揭示了深入系统地分析不同类型土壤(粘土类型不同)中粘土附着态NH_4~+在不同功能微生物作用下的迁移转化过程,是精准评估土壤氮肥施用效率及流失风险的前提之一。     

Salinity Effects on the Adsorption of Nucleic Acid Compounds on Na-Montmorillonite: a Prebiotic Chemistry Experiment

Any proposed model of Earth’s primitive environments requires a combination of geochemical variables. Many experiments are prepared in aqueous solutions and in the presence of minerals. However, most sorption experiments are performed in distilled water, and just a few in seawater analogues, mostly inconsistent with a representative primitive ocean model. Therefore, it is necessary to perform experiments that consider the composition and concentration of dissolved salts in the early ocean to understand how these variables could have affected the absorption of organic molecules into minerals. In this work, the adsorption of adenine, adenosine, and 5’AMP onto Na⁺montmorillonite was studied using a primitive ocean analog (4.0 Ga) from experimental and computational approaches. The order of sorption of the molecules was: 5’AMP?>?adenine > adenosine. Infrared spectra showed that the interaction between these molecules and montmorillonite occurs through the NH₂ group. In addition, electrostatic interaction between negatively charged montmorillonite and positively charge N1 of these molecules could occur. Results indicate that dissolved salts affect the sorption in all cases; the size and structure of each organic molecule influence the amount sorbed. Specifically, the X-ray diffraction patterns show that dissolved salts occupy the interlayer space in Na-montmorillonite and compete with organic molecules for available sites. The adsorption capacity is clearly affected by dissolved salts in thermodynamic terms as deduced by isotherm models. Indeed, molecular dynamic models suggest that salts are absorbed in the interlamellar space and can interact with oxygen atoms exposed in the edges of clay or in its surface, reducing the sorption of the organic molecules. This research shows that the sorption process could be affected by high concentration of salts, since ions and organic molecules may compete for available sites on inorganic surfaces. Salt concentration in primitive oceans may have strongly affected the sorption, and hence the concentration processes of organic molecules on minerals.     

新疆其木干剖面中新世-上新世沉积物粘土矿物特征及其古气候指示意义

为重建新疆其木干地区中新世-上新世古气候,采用X射线衍射、扫描电子显微分析方法,对该区中新世-上新世沉积物中粘土矿物的相对含量、组合类型及显微形貌等进行了研究。结果显示:中新世早期-早中新世中期,沉积物中粘土矿物以伊利石和绿泥石为主,含少量的蒙脱石,表明以干旱气候为特征;晚中新世中期-早中新世晚期,伊利石的相对含量逐渐降低,且含有少量的蒙脱石和高岭石,指示相对温湿的气候条件;中新世晚期的粘土矿物组分与中新世早期相似,以伊利石和绿泥石为主,指示古气候以干旱为主导;晚中新世晚期至上新世伊利石相对含量降低,而蒙脱石和高岭石的相对含量升高,但由于粘土矿物中伊利石、绿泥石的含量仍然较高,指示古气候仍然以干旱为主导,但相对于中新世而言,这段时期为相对湿润期。以上结果表明,新疆其木干地区中新世-上新世古气候以干旱为主,并且气候经历了干旱-相对湿润-干旱-相对湿润的演化过程,但总体而言,本区中新世比上新世要更为干旱。     

Dissolved organic carbon dynamics in the peat–streamwater interface

A series of experiments were conducted to address the fate of dissolved organic carbon (DOC) in the peat–stream interface zone linking a minerotrophic poor fen and an ombrotrophic mire with surrounding stream water in the drainage area of Lake Örträsket in northern Sweden. Transport and mineralisation of DOC were quantified in peat–stream interface cores in response to variations in pore water velocity, DOC concentration and the molecular size and source of DOC. Mineralisation and CH₄ production were positively correlated with pore water velocity at rates between 0.08 and 0.20cmh^–1 and negatively correlated at rates between 0.20 and 0.40cmh^–1. The DOC concentration of the effluent from the peat cores was independent of the pore water velocity but proportional to the DOC concentration of the source water. Higher concentrations of DOC were exported from than imported to the peat cores, and the cores exported DOC molecules of smaller average molecular size than received. Carbon mineralisation in the peat, assessed in a static system, was independent of the concentration of DOC. DOC with a nominal cutoff at 100Da was mineralised faster by streamwater bacteria than DOC dialysed with a cutoff at 3500Da, and their mineralisation rate was positively correlated with the DOC concentration. Streamwater bacteria mineralised streamwater DOC at a lower rate than the peat–stream interface zone pore water DOC. The pattern of velocity dependence of mineralisation was the same for both sources of peat DOC but the mineralisation rates, average molecular size, and bioavailability of DOC were different, emphasising the importance of the compositional heterogeneity of the peat–stream interface zone for the DOC budget of streamwater.     

Clays and other minerals in prebiotic processes

Clays and other minerals have been investigated in context with prebiotic processes, mainly in polymerization of amino acids. It was found that peptides adsorbed on the clay, prior to polymerization, influence the reaction. The ratio between the amount of the peptides adsorbed and that of the clay is important for the yield as well as for the degrees of polymerization obtained. Adsorption prior to reaction produces a certain order in the aggregates of the clay particles which might induce better reaction results. Excess of added peptides disturbs this order and causes lesser degrees of polymerization. In addition to adsorption, clays are also able to occlude between their layers substances out of the environment, up to very high concentrations.     

Interaction between bacteriophage PBS1 and clay minerals and transduction of Bacillus subtilis by clay-phage complexes

Bacteriophage PBS1 of Bacillus subtilis was rapidly adsorbed on montmorillonite (M) and kaolinite (K), and adsorption was maximal after 30 min on both clays. There was no correlation between adsorption and the cation exchange capacity of the clays. Studies with sodium metaphosphate (a polyanion that interacts with positively charged sites on clay) indicated that positively charged sites on K were primarily responsible for the adsorption of the phage, whereas other mechanisms appeared to be involved in adsorption of the phage on M. X-ray diffraction and electron microscopic analyses showed that the phage partially intercalated M. Survival of the phage was increased by adsorption on the clays, and adsorbed phage maintained its ability to transduce bacterial cells for at least 30 days (the longest time studied) after the preparation of the clay–phage complexes. Electron microscopic observations indicated that transduction by the clay–phage complexes was primarily the result of the phage detaching from the clays in the presence of host cells.