•Straw input and rice-growing stimulate soil nitrite oxidizing potential (NO).•Soil NO is related to a shift in Nitrospira-like NOB community structure.•Nitrospira community shift was significantly affected by pH, NH4+ and moisture.•Nitrobacter-like NOB was just not significantly affected in this system.•Nitrospira are more sensitive to straw input and rice-growing than Nitrobacter.Nitrite oxidation is recognized as an essential process of biogeochemical nitrogen cycling in agricultural ecosystems. How nitrite-oxidizing bacteria (NOB) respond to land managements (the effect from the long-term straw incorporation and environmental variability caused by the shift from the upland stage to the paddy stage) in a rapeseed-rice rotation field remains unclear. We found the nitrite oxidation (NO) in soils increased from the upland stage to the paddy stage. An inhibitory effect of the long-term straw incorporation on NO was detectable in the upland stage. The abundance of Nitrospira was always greater than Nitrobacter, and it was affected by the rice-growing and straw incorporation while Nitrobacter was not. NO correlated positively with the abundance of Nitrospira and with soluble sulfate (SO42 −), soil moisture, pH and NH4+. The high-throughput sequencing analysis of the nitrite oxidoreductase nxrA and nxrB genes for Nitrobacter- and Nitrospira-like NOB was performed respectively. The dominating (relative abundance > 1%) operational taxonomic units (OTUs) from Nitrobacter were closely related to Nitrobacter hamburgensis, whereas those from Nitrospira were affiliated with or related to lineage II, lineage V and several unknown groups. Heatmap analysis showed that a few dominant Nitrobacter OTUs were affected by the straw treatment or the rice-growing, and half of the dominant Nitrospira ones were explained by at least one of the variables. Multi-response permutation procedure (MRPP) and redundancy analyses showed that the Nitrospira-like NOB community changes were significantly shaped by the land managements and the soil chemical properties, including pH, moisture and NH4+, whereas that of the Nitrobacter-like NOB community was not. These results suggested that Nitrospira are more sensitive than Nitrobacter to land management in acid and fertilized soils of a rapeseed-rice rotation field trial.Download high-res image (268KB)Download full-size image

•Phosphate-binding is more important in Cd sorption in Gram-negative bacteria.•Non-additivity sorption behavior of Cd on bacteria–clay composites is observed.•Cd-carboxyl/phosphate complexes may act as bridging between bacteria and clays.Bacteria–phyllosilicate complexes are commonly found in natural environments and are capable of immobilizing trace metals. However, the molecular binding mechanisms of heavy metals to these complex aggregates still remain poorly understood. This study investigated Cd adsorption on Gram-positive Bacillus subtilis, Gram-negative Pseudomonas putida and their binary mixtures with montmorillonite using surface complexation model, Cd K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy and isothermal titration calorimetry (ITC). We have shown that larger amounts of Cd are adsorbed by B. subtilis than by P. putida at pH<∼6, and Cd sorption that binding to phosphate groups plays a more important role in P. putida than in B. subtilis. This remind us that we should consider the microbe species when predict the biochemical behavior of trace metals in microbe-bearing environments. The observed Cd adsorption on the binary bacteria–clay composites was more than that predicted based on the component additivity approach. When taking bacteria–clay (1:1 mass ratio) as a representative example, an approximately 68%:32% metal distribution between the bacterial and mineral fraction was found. Both the EXAFS and ITC fits showed that the binding stoichiometry for Cd-carboxyl/phosphate was smaller in the binary mixtures than that in pure bacteria. We proposed that the significant deviations were possibly due to the physical-chemical interaction between the composite fractions that might reduce the agglomeration of the clay grains, increase the negative surface charges, and provide additional bridging of metals ions between bacterial cells and clays.Download high-res image (345KB)Download full-size image

A field experiment was conducted to investigate the effect of chicken manure compost on the fractionation of cadmium (Cd), soil biological properties and Cd uptake by wheat in a soil affected by mining activities in Hubei province, China. Compost was applied at five levels (0, 27, 54, 108, 216 t ha−1), and winter wheat (Triticum aestivum L.) was chosen as an indicator plant. Results showed that the application of compost increased soil pH and the content of total phosphorus and organic matter. Soil biological properties such as microbial biomass carbon, invertase, protease, urease and catalase activities were significantly enhanced by 0.24–3.47 times after compost application. Sequential extraction indicated that compost amendments decreased the acid-extractable Cd by 8.2–37.6 %, while increased the reducible and oxidisable Cd by 9.2–39.5 and 8.2–60.4 %, respectively. The addition of 27–54 t ha−1 compost reduced Cd content in wheat stems and seeds by 69.6–75.0 % and 10.3–18.4 %, respectively. However, only 25.5–26.5 % reductions in Cd content in wheat stems were observed in 108–216 t ha−1 compost amendments, and no significant decrease was detected for seeds. This study suggests that although compost is a suitable organic amendment to improve soil fertility and biological activities, the addition of compost should be moderated by an appropriate rate to optimize the use of compost for the reclamation of metal-contaminated soils at field scale.

Bacterial adhesion to soil particles is fundamentally important in mineral weathering, organic matter degradation, heavy metal transformation, and fate of pollutants. However, the adhesion mechanism between bacteria and soil colloids under continuous flow systems in the natural environments remains unknown.The kinetics of Pseudomonas putida cellular adsorption and desorption on Red soil colloid films under controlled flow systems were examined using in situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Derjaguin–Landau–Verwey–Overbeek (DLVO) and non-DLVO interactions were employed to elucidate the cellular adsorption and desorption kinetics.In situ ATR-FTIR spectroscopy can be used effectively to investigate the kinetics of bacterial adhesion to a soil colloid deposit. Surface proteins may be involved in the bacterial adhesion to soil colloids. The adsorption followed pseudo-first-order kinetic equation. High adsorption rate constant and great saturation coverage of adsorbed bacteria were found at high ionic strengths in dynamic systems.P. putida bacterial cellular adsorption on the soil colloid deposit was irreversible in a wide range of ionic strengths under controlled flow systems. The less reversible adhesion was probably attributed to the DLVO predicted deep secondary energy minima together with non-DLVO factors including polymer bridging, local charge heterogeneities, surface roughness, and Lewis acid–base interactions.

Attachment of bacteria on soil particles is ubiquitous and governs the transformation of nutrients and degradation of pollutants in soil and associated environments. The nature on the binding of bacteria by soil particles has remained unclear. The objectives of the present study were to investigate the adsorption of Pseudomonas putida on particle size fractions from an Ultisol as influenced by solution chemistry and organic matter.An Ultisol was collected from a forest land. One part of the soil was oxidized by H2O2 to remove organic matter. The other part was without such oxidization. Each part of the soil was separated into four size classes: coarse sand (200–2,000 μm), fine sand (20–200 μm), silt (2–20 μm), and clay (<2 μm). The corresponding organic matter-left fractions (OM-left) and organic matter-removed (OM-removed) fractions were obtained. Meanwhile, P. putida was grown in beef extract peptone medium at 28°C to the stationary growth phase. Cells were harvested by centrifugation, washed in deionized water, and resuspended in 10 mM acetate buffer (pH 5.5). Batch experiments were carried out to analyze equilibrium adsorption of bacteria and the effects of pH and electrolyte concentrations on bacterial adsorption.The adsorption isotherms of P. putida on the size fractions conformed to the Langmuir equation. The maximum amount of P. putida adsorbed by clay fraction was 4.3 and 62.3 times as great as that by silt and sand fractions, respectively. The number of P. putida attached to OM-removed fractions was significantly larger than that to OM-left fractions. P. putida adsorption on OM-left fractions with increasing pH from 4.0 to 9.0 was reduced by 44.0–78.8%. At the same time, further decreases (7.5–21.1%) were observed in the adsorption for OM-removed ones. Mg2+ was much more effective than Na+ in enhancing P. putida attachment. Na+ and Mg2+ ions more strongly promoted P. putida adsorption on OM-left fractions than on OM-removed fractions.Clay fraction presented the largest adsorption capacity for bacteria, followed by soil silt and sand fractions. As compared with silt and sand fractions, it is likely that the greater amounts of bacteria adsorbed by clay fractions were attributed to their higher content of clay minerals and iron oxides. Soil organic matter plays a suppressive role in the interfacial processes occurring during the initial bacterial attachment.

The contamination of agricultural soils by heavy metals is a worldwide problem. Organic amendments can be used for the immobilization and binding of heavy metal ions in soils by complexation, adsorption, and precipitation. A field trial was carried out to evaluate the influence of some low-cost organic materials such as rice straw (RS), green manure (GM), and pig manure (PM) on the distribution of Cu and Cd and the retention of these metals by organic matter fractions in heavy metal-polluted soils.The experiment was conducted in Miaoyunao Village, Daye County, Hubei province, China. PM, GM (peanut plants), and RS were obtained from a farm close to the village. Sixteen treatments with three replicates were designed. Soil chemical properties such as soil pH, electrical conductivity (EC), organic matter (OM), and available P were measured by standard methods. Soluble/exchangeable, organic-bound, inorganic precipitates and residual Cu and Cd in the soil were sequentially extracted and analyzed. The amounts of Cu and Cd bound with soil particulate organic matter (POM) fractions and humic substances were also determined.The addition of organic amendments declined significantly the concentrations of soluble/exchangeable Cu and Cd, but increased the amounts of these metals in organic-bound and inorganic precipitate forms in the soil. RS was more effective than GM and PM in diminishing the solubility of Cu and Cd. The largest retention for Cu and Cd by humic substances and POM was noticed in RS treatments, whereas the lowest was found in PM treatments. Humic substances showed higher potential in the fixation of Cu and Cd than POM fractions. The conversion of soluble/exchangeable Cu and Cd to other insoluble forms after the application of organic amendments may be ascribed to the increases of soil OM, pH, EC, and available P contents. The highest binding of Cu and Cd with POM fractions and humic substances after the incorporation of RS mainly resulted from the greatest increase of soil OM contents.RS, GM, and PM can be employed as good and cheap substances for the immobilization of Cu and Cd in heavy metal-polluted soils. RS was the best amendment in decreasing the solubility of Cu and Cd, and also in enhancing the retention of these metals by humic substances and POM fractions in the soil. Futures studies should focus on the influence of these organic amendments or their mixtures on the phytotoxicity of Cu and Cd for different plants in heavy metal-contaminated soils.

Equilibrium adsorption along with scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and isothermal titration calorimetry (ITC) techniques were employed to investigate the adhesion of Pseudomonas putida on goethite. The adhesion isotherm revealed the high affinity of P. putida for goethite. The SEM analysis also showed a tight association between bacteria and mineral particles. Larger amounts of adhesion of bacteria on goethite were observed at pH lower than the isoelectric point (IEP) of goethite. The bacterial adhesion increased with increasing concentration of K+. The calorimetric results demonstrated that the P. putida–goethite adhesion was an exothermic process. The adhesion enthalpy increased with increasing pH and concentrations of electrolyte. The increase of the negative enthalpy with increment of temperature indicated that the bacteria–goethite adhesion was an enthalpy-driven process. Electrostatic interactions and hydrogen bonding were considered to contribute mainly to the adhesion of bacterial adhesion on goethite. The data obtained in this study would provide valuable information for a better understanding of the mechanisms of mineral–microorganism interactions in soil and associated environments.

Acid phosphatase was immobilized on layered double hydroxides of uncalcined- and calcined-Mg/Al-CO3 (Unc-LDH-CO3, C-LDH-CO3) by the means of direct adsorption. Optimal pH and temperature for the activity of free and immobilized enzyme were exhibited at pH 5.5 and 37 °C. The Michaelis constant (Km) for free enzyme was 1.09 mmol mL−1 while that for immobilized enzyme on Unc-LDH-CO3 and C-LDH-CO3 was increased to 1.22 and 1.19 mmol mL−1, respectively, indicating the decreased affinity of substrate for immobilized enzymes. The residual activity of immobilized enzyme on Unc-LDH-CO3 and C-LDH-CO3 at optimal pH and temperature was 80% and 88%, respectively, suggesting that only little activity was lost during immobilization. The deactivation energy (Ed) for free and immobilized enzyme on Unc-LDH-CO3 and C-LDH-CO3 was 65.44, 35.24 and 40.66 kJ mol−1, respectively, indicating the improving of thermal stability of acid phosphatase after the immobilization on LDH-CO3 especially the uncalcined form. Both chemical assays and isothermal titration calorimetry (ITC) observations implied that hydrolytic stability of acid phosphatase was promoted significantly after the immobilization on LDH-CO3 especially the calcined form. Reusability investigation showed that more than 60% of the initial activity was remained after six reuses of immobilized enzyme on Unc-LDH-CO3 and C-LDH-CO3. A half-life (t1/2) of 10 days was calculated for free enzyme, 55 and 79 days for the immobilized enzyme on Unc-LDH-CO3 and C-LDH-CO3 when stored at 4 °C. Therefore, immobilization of acid phosphatase on Unc-LDH-CO3 and C-LDH-CO3 by direct adsorption is an effective means and would have promising potential for the practical application in agricultural production and environmental remediation.

In this study, Fourier transform infrared spectroscopy, potentiometric titration, along with sorption experiments using chemically modified bacteria were conducted to compare the behavior of Gram-positive Bacillus thuringiensis and Gram-negative Escherichia coli as sorbents for Cu2+ and Cd2+ ions. The IR spectra showed that there were obvious changes connected with the–COOH groups for Cu(II)- and Cd(II)-loaded B. thuringiensis. A three site non-electrostatic model provides an excellent fit to the titration curves of both E. coli and B. thuringiensis with the first corresponding pKa values of 4.16 ± 0.18 and 3.30 ± 0.24, respectively, implying that B. thuringiensis contains more carboxyl groups than E. coli. Chemical modification and metal sorption experiments further confirmed that carboxyl groups may play a more important role in the binding Cd(II) and Cu(II) for B. thuringiensis than for E. coli, which could be attributed to the higher concentration of carboxyl sites of B. thuringiensis than E. coli. These results show that the main chemical functional group responsible for the binding of metal ions on B. thuringiensis and E. coli is obviously different because of the different composition and structure of bacterial cell walls. The concentrations of the chemical functional groups on bacterial cell walls are regarded to govern their role in the binding of metal ions and affect the affinity between the bacterial cells and metal ions.

Adsorption and desorption of salmon sperm DNA on bacteria (Bacillus thuringiensis, Pseudomonas putida), two different colloidal fractions (organic and inorganic clay) from an Alfisol, minerals (montmorillonite, kaolinite and goethite) and colloid–bacteria composites were studied. Similar adsorption capacity and affinity of DNA were observed on two bacterial cells. However, the two bacterial strains played different roles in affecting the adsorption of DNA on the composites of soil colloidal particles with bacteria. The introduction of B. thuringiensis in soil colloids and minerals systems dramatically promoted DNA adsorption on colloidal particles especially organic clay, while P. putida decreased the adsorption of DNA on kaolinite and goethite. Electrostatic force and ligand exchange are regarded to be the major driving forces involved in the adsorption of DNA on bacterial cells, montmorillonite, soil colloids and goethite. Presence of bacteria enhanced the proportion of DNA adsorption on soil colloidal particles by electrostatic force and depressed that by ligand exchange process. Information obtained in this study is of fundamental significance for the understanding of the ultimate fate of extracellular DNA in soil systems.

The present study was carried out to investigate the conformation, enzymatic activity and proteolytic stability of acid phosphatase on montmorillonite, kaolinite and soil colloids from an Alfisol by means of circular dichroism (CD) spectroscopy, isothermal titration microcalorimetry (ITC) and biochemical assay, respectively. The results showed that the secondary structure of phosphatase was changed from disordered type to ordered form during adsorption/desorption cycle, organic substance and 2:1-clay mineral in Brown Soil benefited the formation of ordered structure. Enzymatic activity of phosphatase was inhibited while the proteolytic stability was promoted after the interaction with active particles from permanent charge soil. The decrease of enzymatic activity and the increase of proteolytic stability resulted by montmorillonite and organic colloid were both greater than that by kaolinite and inorganic colloid, which was in consistent with the extent of structural change induced by different colloid particles. Thus, one of the most significant factors responsible for the variation of enzymatic activity and proteolytic stability might be the hiding or even damage of active sites and the irrecognition of cleavage sites in enzyme molecules induced by the formation of ordered structure. The information obtained in this study is of crucial significance for the understanding of the behavior and fate of extracellular enzymes in soils with permanent charges.

Two Hg2+-specific biosensors were constructed using bacterial luciferase as reporter gene and plasmid-free Pseudomonas putida X4 and Enterobacter aerogenes NTG-01 as host strains. The performance of X4 biosensor was compared with that of NTG-01 biosensor in the same assay conditions. The maximum bioluminescence for X4 (pmerRluxCDABE-Kan) biosensor was found during the midexponential phase and that for NTG-01 (pmerRluxCDABE-Kan) was at the late exponential phase. The shortest induction time of two biosensors was 30 min. The maximum light signal output for NTG-01 and X4 sensors was observed at the incubation time of 5 and 4 h, respectively. The lowest detectable concentration of mercury by the two biosensors were both of 100 pM at 28°C, pH 7 and an initial cell number of 106 CFU ml−1. Cd2+, Zn2+, Co2+, Cu2+, and Pb2 + ions at nanomolar level did not interfere with the measurement by the biosensors. These results show that the sensitivity of the two biosensors is sufficient for the detection of Hg2+ under most contaminated environments.

Adsorption, desorption and degradation by DNase I of DNA on montmorillonite (M) and different hydroxyaluminum-M complexes (Al(OH)x-M) containing 2.5, 10.0 and 20.0 mmol coated Al/g clay (AM2.5, AM10 and AM20) were studied. The adsorption isotherms of DNA on montmorillonite and Al(OH)x-M complexes conformed to the Langmuir equation. The amount of DNA adsorbed followed the sequence of montmorillonite > AM20 > AM10 > AM2.5. A marked decrease in the adsorption of DNA on montmorillonite and Al(OH)x-M complexes was observed with the increase of pH from 4.0 to 9.0. Calcium ion significantly promoted DNA adsorption. The adsorption enthalpy of DNA on montmorillonite was endothermic, whereas that on Al(OH)x-M complexes was exothermic. The percent desorption of DNA from clays was in the order of montmorillonite > AM2.5 > AM10 > AM20, suggesting that OH–Al loading on montmorillonite surface increased the binding affinity of DNA. Fourier transform infrared (FTIR) spectra showed that the binding of DNA on AM10 and AM20 changed its conformation from the B-form to the Z-form. The presence of montmorillonite and Al(OH)x-M complexes provided protection for DNA against degradation by DNase I. The higher level of protection was found with Al(OH)x-M complexes compared to montmorillonite. The higher stability of DNA in the system of Al(OH)x-M complexes seemed to be attributed mainly to the conformational change of bound DNA and their greater adsorption capacity for DNase I. The information obtained in this study is of fundamental significance for understanding the behavior of extracellular DNA in soil environments.

Equilibrium adsorption along with isothermal titration calorimetry (ITC), Fourier transform infrared spectra (FTIR) and scanning electron microscopy (SEM) techniques were employed to investigate the adsorption of Pseudomonas putida on kaolinite and montmorillonite. A higher affinity as well as larger amounts of adsorption of P. putida was found on kaolinite. The majority of sorbed bacterial cells (88.7%) could be released by water from montmorillonite, while only a small proportion (9.3%) of bacteria desorbed from kaolinite surface. More bacterial cells were observed to form aggregates with kaolinite, while fewer cells were within the larger bacteria–montmorillonite particles. The sorption of bacteria on kaolinite was enthalpically more favorable than that on montmorillonite. Based on our findings, it is proposed that the non-electrostatic forces other than electrostatic force play a more important role in bacterial adsorption by kaolinite and montmorillonite. Adsorption of bacteria on clay minerals resulted in obvious shifts of infrared absorption bands of water molecules, showing the importance of hydrogen bonding in bacteria–clay mineral adsorption. The enthalpies of −4.1 ± 2.1 × 10−8 and −2.5 ± 1.4 × 10−8 mJ cell−1 for the adsorption of bacteria on kaolinite and montmorillonite, respectively, at 25 °C and pH 7.0 were firstly reported in this paper. The enthalpy of bacteria–mineral adsorption was higher than that reported previously for bacteria–biomolecule interaction but lower than that of bacterial coaggregation. The bacteria–mineral adsorption enthalpies increased at higher temperature, suggesting that the enthalpy–entropy compensation mechanism could be involved in the adsorption of P. putida on clay minerals. Data obtained in this study would provide valuable information for a better understanding of the mechanisms of mineral–microorganism interactions in soil and associated environments.

Adsorption of Pseudomonas putida on minerals including montmorillonite, kaolinite and goethite was studied. The adsorption isotherms of P. putida on the examined minerals conformed to the Langmuir equation. The amount of P. putida adsorbed followed the order: goethite > kaolinite > montmorillonite. A greater extent of P. putida adsorption on minerals was observed in the range of temperature from 15 to 35 °C. The adsorption of P. putida on minerals decreased with the increase of pH from 3.0 to 10.0. Magnesium ion was more efficient than sodium ion in promoting P. putida adsorption on minerals. The results suggest that electrostatic interactions play a vital role in P. putida adsorption by soil colloidal factions. The information obtained in this study is of fundamental significance for the understanding of the survival and transport of bacteria in soil systems.

•High efficiency of growing fungus strain XLA in reducing Cr6+.•Biotransformation, biosorption and bioaccumulation are involved in reducing Cr6+.•Extra/intracellular defense systems of XLA are contributed to Cr6+ detoxification.•Responses of Cr defense systems to various Cr6+ levels are diverse.In the study, the capability of Paecilomyces lilacinus XLA (CCTCC: M2012135) to reduce Cr6+ and its main antagonistic mechanisms to Cr6+ were experimentally evaluated. Activated growing fungus XLA efficiently reduced over 90% Cr6+ in the media with Cr6+ concentration below 100 mg L−1 at pH 6 after 14 days. After 1-day exposure to 100 mg L−1 Cr6+, nearly 50% of Cr6+ was reduced. Moreover, SO42− stimulated Cr6+ reduction, whereas other interferential ions inhibited Cr6+ reduction. The interaction mechanisms between XLA and Cr6+ mainly involve biotransformation, biosorption, and bioaccumulation, as detected by electron microscopy and chemical methods. The lower concentrations of Cr6+ (5 and 50 mg L−1) stimulated the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH) level in XLA, respectively, but the higher concentration of Cr6+ (150 mg L−1) decreased the enzymatic activities and GSH concentration. The results implied that SOD, CAT and GSH were defensive guards to the oxidant stress produced by Cr6+. All these extracellular/intracellular defense systems endowed XLA with the ability to resist and detoxify Cr6+ by transforming its valent species. The fungus XLA could efficiently reduce Cr6+ under different environmental conditions (pH, interferential ions, and concentration). Moreover, XLA could endure the high concentration of Cr6+ probably due to its high biotransformation capability of Cr6+ and intracellular antioxidant systems for the detoxification of ROS generated by external Cr6+. All these results suggested that the fungus XLA can be applied to remediation of Cr6+-contaminated environments.Download high-res image (182KB)Download full-size image

In situ immobilization of heavy metals via physical, chemical, and biological processes presents practical remediation techniques for contaminated agricultural soils. In the current study, plant yield and cadmium (Cd) uptake by pakchoi (Brassica chinensis L.) in relation to soil Cd fractionations were investigated to evaluate the remediating effect of EGFP-tagged Pseudomonas putida X4 in Cd-contaminated soil. The soil treated with various levels of Cd (0–10 mg kg−1 soil) was inoculated with P. putida X4::gfp at an initial cell density of 107. Bacterial application transformed 7.5%–24.8% of soluble/exchangeable Cd mainly to the organic-bound fraction. Cd uptake decreased in pakchoi shoots by 10.0%–62.0% and pakchoi roots by 8.1%–60.1% after microbial remediation. The test bacterium was able to rapidly colonize the Cd-contaminated habitats and could persist at relatively stable cell densities during the whole pot experiments. This low cost and eco-friendly remediation method is very effective in the restoration of Cd-contaminated soils.Highlights► Inoculation of Pseudomonas putida X4 in contaminated soil reduced substantially the bioavailability of Cd for pakchoi plants. ► Pseudomonas putida X4 was efficient in transforming and stabilizing soil Cd species. ► Pseudomonas putida X4 could rapidly colonize the Cd-contaminated habitats and persist at relative stable cell densities in soil. ► Pseudomonas putida X4 showed prominent potentials in the restoration of Cd-contaminated soils.

The growth performance of pakchoi (Brassica chinensis L.) in relation to soil cadmium (Cd) fractionations was investigated to evaluate the remediating effect of poultry manure compost on Cd-contaminated soil. A yellow-brown soil (Alfisol) treated with various levels of Cd (0–50 mg Cd kg−1 soil) was amended with increasing amounts of compost from 0 to 120 g kg−1. Compost application transformed 47.8%–69.8% of soluble/exchangeable Cd to the organic-bound fraction, and consequently decreased Cd uptake of pakchoi by 56.2%–62.5% as compared with unamended soil. Alleviation of Cd bioavailability by compost was attributed primarily to the increase of soil pH and complexation of Cd by organic matter including dissolved organic matter. In general, the improvement of pakchoi performance was more pronounced in higher Cd-contaminated soil. Addition of large amount of compost also favored the anti-oxidative capability of pakchoi against Cd toxicity. This low cost remediation method seems to be very effective in the restoration of Cd-contaminated soils.

The growth performance of pakchoi (Brassica chinensis L.) in relation to soil cadmium (Cd) fractionations was investigated to evaluate the remediating effect of poultry manure compost on Cd-contaminated soil. A yellow-brown soil (Alfisol) treated with various levels of Cd (0–50 mg Cd kg−1 soil) was amended with increasing amounts of compost from 0 to 120 g kg−1. Compost application transformed 47.8%–69.8% of soluble/exchangeable Cd to the organic-bound fraction, and consequently decreased Cd uptake of pakchoi by 56.2%–62.5% as compared with unamended soil. Alleviation of Cd bioavailability by compost was attributed primarily to the increase of soil pH and complexation of Cd by organic matter including dissolved organic matter. In general, the improvement of pakchoi performance was more pronounced in higher Cd-contaminated soil. Addition of large amount of compost also favored the anti-oxidative capability of pakchoi against Cd toxicity. This low cost remediation method seems to be very effective in the restoration of Cd-contaminated soils.

The adsorption and desorption of the toxin from Bacillus thuringiensis strain WG-001 on rectorite were studied at different toxin and/or rectorite concentrations, pH values and temperatures. The insecticidal activity of the adsorbed toxin was evaluated by determining the lethal concentration to kill 50% of the larvae of Heliothis armigera (LC50). The adsorption of the toxin on rectorite in sodium carbonate buffer (pH 9) reached equilibrium within 0.5–1.0 h and the adsorption isotherm of the toxin followed the Langmuir equation (R2 > 0.99). In the pH range from 9 to 11 (carbonate buffer), the adsorbed toxin decreased with increasing pH. The adsorption amounts decreased with increasing rectorite:toxin ratio. The adsorption was not significantly affected by the temperature between 10 and 50 °C. The X-ray diffraction analysis indicated occurrence of the intercalation of the rectorite by the toxin. The infrared absorption spectrum showed that the binding of the toxin did not alter its structure. The LC50 values of the adsorbed toxin were smaller than those of the free toxin. The rectorite protected the toxin from ultraviolet irradiation damage. The desorption of the adsorbed toxin in water ranged from 37.5% to 56.4% and from 27.4% to 41.8% in a carbonate buffer. The desorption percentage also decreased with increasing rectorite:toxin ratio.

Isothermal microcalorimetry provides thermodynamic and kinetic information on various reactions and processes and is thereby a powerful tool to elucidate their mechanisms. Certain improvement in isotherma! microcalorimetry with regard to the studies on soil and environmental sciences is briefly described. This review mainly focuses on the use of microcalorimetry in the determination of soil microbial activity, monitoring the toxicity and biodegradation of soil organic pollutants, the risk evaluation of metals and metalloids, the heat effect of ion exchange and adsorption in soil, and environmental researches. Promising prospects for the applications of the technique in the field are also discussed.

Polymerase chain reaction (PCR) was used to amplify a 600-base pair (bp) sequence of plasmid pGEX-2T DNA bound on soil colloidal particles from Brown soil (Alfisol) and Red soil (Ultisol), and three different minerals (goethite, kaolinite, montmorillonite). DNA bound on soil colloids, kaolinite, and montmorillonite was not amplified when the complexes were used directly but amplification occurred when the soil colloid or kaolinite-DNA complex was diluted, 10- and 20-fold. The montmorillonite-DNA complex required at least 100-fold dilution before amplification could be detected. DNA bound on goethite was amplified irrespective of whether the complex was used directly, or diluted 10- and 20-fold. The amplification of mineral-bound plasmid DNA by PCR is, therefore, markedly influenced by the type and concentration of minerals used. This information is of fundamental importance to soil molecular microbial ecology with particular reference to monitoring the fate of genetically engineered microorganisms and their recombinant DNA in soil environments.