Stabilization of chromium(VI) by hydroxysulfate green rust in chromium(VI)-contaminated soils

Chromium (Cr)-contaminated soils pose a great environmental risk, with high solubility and persistent leaching of Cr(VI). In this study, hydroxysulfate green rust (GR_SO4), with the general formula Fe(II)₄Fe(III)₂(OH)₁₂SO₄·8H₂O, was evaluated for its efficiency in Cr(VI) stabilization via Cr(VI) reduction to Cr(III) in four representative Cr(VI)-spiked soils. The initial concentrations of phosphate buffer-extractable Cr(VI) (Cr(VI)_b) in soils 1, 2, 3, and 4 were 382.4, 575.9, 551.3, and 483.7 mg kg^-1, respectively. Reduction of Cr(VI) to Cr(III) by structural Fe(II) (Fe(II)_s) in GR_SO4 in all studied soils was fast, wherein the application of GR_SO4 markedly decreased the amount of Cr(VI)_b at the Cr(VI)_b/Fe(II)_s stoichiometric mole ratio of 0.33. The kinetics of Cr(VI) reduction by GR_SO4 could not be determined as this reaction coincided with the release of Cr(VI) from soil during the experiment. The concentration of Cr(VI)_b decreased, as the Cr(VI)_b/Fe(II)_s ratio decreased from 0.46 to 0.20, generally to below 10 mg kg^-1. Back-transformation of the generated Cr(III) was examined in the presence of manganese oxide birnessite at the birnessite/initial Cr(III) mole ratio of 4.5. The results of batch tests showed that only 5.2% of the initial Cr(III) was converted to Cr(VI) after two months, while under field capacity moisture conditions, less than 0.05% of the initial Cr(III) was oxidized to Cr(VI) after six months. The results illustrated that remediation of Cr(VI)-contaminated soils would be fast, successful, and irreversible with an appropriate quantity of fresh GR_SO4.     

Removal of chromium (VI) as chromium diphenyl carbazide (CDC) complex from aqueous solution by activated carbon

Adsorption of Cr (VI) as CDC-complex from aqueous solution by activated C has been investigated. Factors like pH and presence of Cr (III) which affect the adsorption of CDC-complex were studied. The increase in particle size and surface area of activated C does not enhance the removal of CDC-complex. For different concentrations of Cr, the optimum quantity of Diphenyl Carbazide has been determined. The reduced Cr e.g. Cr (III) decreases the CDC-complex removal. The Langmuir and Freundlich isotherms constant as calculated are γm=1.8932 and b=0.2305 and n=0.036, log K=0.0266, respectively.     

Molecular characterization of chromium (VI) reducing potential in Gram positive bacteria isolated from contaminated sites

Hexavalent chromium [Cr(VI)] is highly toxic, teratogenic and carcinogenic to man and other animals. Some bacterial species have the ability to reduce Cr(VI) to a stable speciation state of trivalent chromium [Cr(III)], which is insoluble and comparatively less toxic. Therefore, the reduction of Cr(VI) thus provides potential as a means for environmental bioremediation of Cr(VI) pollution. In the present study bacteria isolated from chromium and diesel contaminated sites were found to have the ability to rapidly reduce highly toxic concentrations of Cr(VI) to Cr(III) when grown in minimal medium supplemented with glucose as the sole carbon source. Partial chromate reductase gene sequences were retrieved after PCR amplification of genomic DNA extracted from three Gram positive isolates which were highly similar (>99% sequence similarity) to chromate reductase genes found in Gram negative bacteria, more specifically those identified from Escherichia coli and Shigella spp. whole-genome studies. The isolated bacteria were putatively identified by 16S rRNA gene sequencing as Arthrobacter aurescens strain MM10, Bacillus atrophaeus strain MM20, and Rhodococcus erythropolis strain MM30.     

Effect of chromium VI on mineral element composition of bush beans

Bush beans (Phaseolus vulgaris L. cv Contender) were grown on perlite with nutrient solution and 0, 1, 2.5 and 5 ppm levels of Na₂CrO₄ Significant decrease of top growth and chlorosis in trifoliated leaves were observed for 2.5 and 5 ppm Cr, with Cr concentrations (μg/g) in tops:≥ 12.1, in roots:≥ 509.9. Cr decreased K, Na, Mg and Fe concentrations, and increased P and Mn concentrations in roots. In tops decreased N, K, Na and Fe concentrations and increased Mn and Ca concentrations were observed, Translocation of P, Zn, Cu and Fe was inhibited; Ca and Mn translocation was generally enhanced. P/Fe ratio was increased up to 60% in chlorotic plants, indicating a shift from Fe²⁺ to Fe³⁺.     

Retention of vanadium (V) by three Finnish mineral soils

Retention of V(V) by three Finnish mineral soils from 10^?4m and 10^?5m sodium vanadate solutions was investigated at room temperature in the pH range 2.3–7.5. In adsorption experiments, 0.02 m KCl was used as ionic medium, and the samples were left to equilibrate for 72 h. The solid: solution ration was 1:100 (m: v). Maximum adsorption occurred at pH ～4, where 70–80% of the added V (350–400 μg g^?1 from 10^?4m solution and 35–40 μg g^?1 from 10^?5m solution) was retained by each soil. Retention was significant even at pH 6, where adsorption of a similar anion, molybdate, is negligible. Desorption of the retained V was measured by adding 50.0 cm³ of 0.02 M KCl into weighed soil samples and shaking for 17 h in a mechanical stirrer. Only a minor part of retained V could be removed from each soil by the KCl treatment. Retention of different ionic species of V from 10^?5m solution is approximated using values of log K obtained from the literature. In these calculations, kaolin is used as a reference material.     

Characterization of Desulfovibrio sp. isolated from some lowland paddy field soils of Burkina Faso

In a wetland ecosystem such as lowland ricefields, the anaerobic mineralization of organic matter is a key mechanism for nutrient recycling (Jørgensen 1982; Freney et al. 1982). In the process which involves several bacterial groups, sulfate reducers (Watanabe and Furusaka 1980; Widdel 1988; Ouattara and Jacq 1992; Nozoe 1997), methanogens (Asakawa and Hayano 1995; Dianou et al. 1997), sulfur and ferric ion reducers (Jacq et al. 1991) become active when the soil becomes anoxic (Amstrong 1969). Sulfate reducers are common in flooded soils (Watanabe and Furusaka 1980; Widdel 1988; Furusaka et al. 1991). Reported densities in rice soils ranged from 10³ to 10⁵ g^-1 dry soils in Asia (Watanabe and Furusaka 1980) and from 10² to 10⁹ g^-1 dry soil in Sénégal (Ouattara and Jacq 1992). Among the sulfate reducers, the “classical” Desulfovibrio species are known to oxidize typical fermentation products such as hydrogen, lactate, pyruvate, and dicarboxylic acids (Widdel 1988). So far, data on the isolation and characterization of sulfate-reducing bacterial (SRB) strains from African rice paddy field soils study have been very limited.     

Nodulation of African yam bean (Sphenostylis stenocarpa) by Bradyrhizobium sp. isolated from Erythrina brucei

African yam bean (Sphenostylis stenocarpa), which is widely cultivated in Africa because of its growth capability on marginal soils, was nodulated by an endosymbiont (characterized and designed Bradyrhizobium sp. AUEB20) isolated from the Ethiopian tree Erythrina brucei with the formation of a small number of large, indeterminate N₂-fixing nodules. In contrast, 24 other isolates from Ethiopian woody legumes were ineffective. Strain AUEB20 promiscuously nodulated a number of tropical legumes, but none out of five European crop plants tested. Received: 17 September 1996     

Validation of an electrothermal atomization atomic absorption spectrometry method for quantification of total chromium and chromium(VI) in wild mushrooms and underlying soils

An ETAAS method was validated to quantify total Cr and Cr(VI) in mushrooms and the underlying soils. The method includes a sample pretreatment for total Cr dissolution using a wet acid digestion procedure and a selective alkaline extraction for Cr(VI). The limits of detection were, expressed in microg/L, 0.15 and 0.17 for total Cr and Cr(VI), respectively. The linearity ranges under the optimized conditions were 0.15-25.0 and 0.17-20.0 microg/L for total Cr and Cr(VI), respectively. The limits of quantification were, expressed in microg/g of dry weight, 0.0163 and 0.0085 for total and hexavalent chromium, respectively. The precision of the instrumental method for total Cr and Cr(VI) was lower than 1.6%, and for the analytical method, it was lower than 10%. The accuracy of the method for Cr(VI) quantification was evaluated by the standard additions method, with the recoveries being higher than 90% for all of the added concentrations. For total Cr, certified reference materials (lichen CRM 482 and soil sample NCS ZC73001) were used. An interference study was also carried out in a mushroom simulated matrix, and it was verified that the deviations of the expected values were lower than 4.0% for both total Cr and Cr(VI). The validated method was applied to the evaluation of total Cr and Cr(VI) in 34 wild mushrooms and 34 respective underlying soil samples collected in two different regions of Portugal (Beira Interior and TrAs-os-Montes), with different locations regarded as noncontaminated or contaminated areas. The species were identified by a mycologist and subdivided into 10 genera and 15 species: Amanita (rubescens, muscaria, and ponderosa), Boletus (regius), Lactarius (deliciosus, vellereus, and piperatus), Suillus (granulatus and luteus), Tricholoma (acerbum), Agaricus (sylvicola), Volvariella (gloiocephala), Lecopaxillus (giganteus), Macrolepiota (procera), and Psilocybe (fascicularis). The mean values found for total Cr were 1.14 and 1.11 microg/g of dry weight, and for Cr(VI), the mean values were 0.103 and 0.143 microg/g of dry weight for cap and stalk, respectively. For soils, the mean concentrations found were, for total Cr, 84.0 microg/g and, for Cr(VI), 0.483 microg/g. The bioconcentration factors (BCFs) based on dry weight for cap and stalk were determined, and the values found, for both total Cr and Cr(VI), were always <1, although for hexavalent chromium, the BCFs were 10 times higher than for total chromium.     

Resistance of mineral soils to Fe(III) reduction

Gleying and enhancement of hydromorphism in wetland soils due to Fe(III) reduction entail a series of degradation processes. The resistance of wetlands to degradation can be calculated from the content of potentially reducible iron, Fe(III)_pr, which is found from the van Bodegom equation taking into account the contents of oxalate-soluble iron Fe_ox and dithionite-soluble iron Fe_dit in the soil. In addition, this makes it possible to distinguish relict and actual gleysols. The van Bodegom equation is applicable to soils from which the oxalate solution extracts only amorphous and poorly crystallized iron compounds, which are quickly reduced by Fe-reducing bacteria. These soils have a low proportion of Fe(II) (no more that 15% of the total iron), as well as an accumulative profile distribution of Fe_ox. The van Bodegom equation is unsuitable for calculating the Fe(III)_pr content in soils with a high proportion of Fe(II) and a nonaccumulative profile distribution of Fe_ox.     

Treatment of Cr(VI)-spiked soils using sulfur-based amendments

The objective of this research was to assess the hexavalent chromium (Cr(VI)) reducing efficiency of sulfur-based inorganic agents including calcium polysulfide (CPS), iron sulfide (FeS), pyrite (FeS₂) and sodium sulfide (Na₂S) in three soils. An alkaline soil (soil 1), a neutral soil (soil 2) and a slightly acid soil (soil 3) constituted the investigated soils. The soils were spiked with two levels of Cr(VI) (100 and 500 mg Cr(VI) kg^?1 soil) and incubated at field capacity (FC) for one month. Then, CPS, FeS, FeS₂ and Na₂S were added at 0, 5 and 10 g kg^?1 and the concentrations of exchangeable Cr(VI) were measured after 0.5, 4, 48 and 168 h in a batch experiment. The pH and organic carbon content of the soils played predominant role in Cr(VI) self-reduction by the soil itself. Complete self-reduction of Cr(VI) from soils 1, 2 and 3 was achieved at maximum Cr(VI) levels of 1, 50 and 500 mg kg^?1, respectively. Therefore, the concentration of Cr(VI) should not exceed the given levels in order to ensure that Cr(VI) is not released into the environment from contaminated sites. Moreover, decreasing pH in the alkaline soil caused significant increase of Cr(VI) reducing efficiency. Na₂S, CPS and FeS, in contrast to FeS₂, were efficient Cr(VI) reducing agents in all three soils. For all added amendments the following order of Cr(VI) reducing capacity was observed: Na₂S > CPS > FeS > FeS₂ in soil 1, Na₂S ? CPS ~ FeS > FeS₂ in soil 2 and Na₂S ? FeS > CPS ~ FeS₂ in soil 3.     

PAH biodegradation by telluric saprotrophic fungi isolated from aged PAH-contaminated soils in mineral medium and historically contaminated soil microcosms

Journal of Soils and Sediments - Remediation of contaminated soils is of high relevance considering losses of this limited resource in most countries through erosion or through destruction for...     

Nature of antagonism of fungi by bacteria isolated from soils

The influence of 457 bacteria isolated from soil on spore germination by Aspergillus flavus was studied by light and scanning microscopy. Bacteria were found to be in physical association with the fungus. The bacteria were tested for antagonism against 11 fungal phytopathogens. A number of the bacterial antagonists displayed a wide spectrum in their activity against the fungi.     

防治蔬菜枯萎病的芽孢杆菌对植物体内酶活性的影响

将拮抗菌制成液体培养,黄瓜、西瓜、青椒经处理后测定其体内几种酶活性的变化研究结果表明,3种植物经5个菌株的液体培养处理后,其多酚氧化酶、过氧化氢酶、β-1,3-葡聚糖酶活性比对照均有明显提高,98-Ⅱ和96-Ⅱ使青椒、黄瓜多酚氧化酶活性分别提高477.78％和150.00％;96-Ⅱ和94-Ⅲ使黄瓜过氧化氢酶活性分别提高419.64％和115.66％;94-Ⅱ使西瓜过氧化氢酶活性提高109.24％;98-Ⅰ使黄瓜β-1,3-葡聚糖酶活性提高23.90％。拮抗菌处理后诱导植物体内产生一些有益于植物抗病性增强的生理生化反应,是拮抗菌制剂防病的机理之一。     

Purification and characterization of a novel fibrinolytic enzyme from Bacillus sp. nov. SK006 isolated from an Asian traditional fermented shrimp paste

Bacillus sp. nov. SK006 producing four extracellular fibrinolytic enzymes was isolated from fermented shrimp paste, a traditional and popular Asian seasoning. One fibrinolytic enzyme was purified to homogeneity with a molecular mass of 43-46 kDa by SDS-PAGE and gel filtration chromatography. The specific activity was determined to be 11.2 units/mg using plasmin as a standard. The enzyme displayed optimal activity at 30 degrees C and pH 7.2. It was stable below 40 degrees C for 4 h between pH 5.0 and pH 11.0. Zinc ion stimulated the enzyme activity whereas Cu2+, Ca2+, Fe3+, and Hg2+ caused its inhibition. The fibrinolytic activity was strongly inhibited by PMSF and moderately inhibited by EDTA as well as PCMB. The enzyme exhibited a higher affinity toward N-Succ-Ala-Ala-Pro-Phe-pNA and was able to degrade fibrin clots either by forming active plasmin from plasminogen or by direct fibrinolysis. The N-terminal amino acid sequence was found to be AQSVPYEQPHLSQ, which is different from that of other known fibrinolytic enzymes.     

Application of plant growth-promoting endophytes (PGPE) isolated from Solanum nigrum L. for phytoextraction of Cd-polluted soils

Many plant growth-promoting endophytes (PGPE) can assist their host plants cope with contaminant-induced stress responses, which can improve plant growth. In this study, four heavy metals resistant endophytic bacteria, Serratia nematodiphila LRE07, Enterobacter aerogenes LRE17, Enterobacter sp. LSE04 and Acinetobacter sp. LSE06, were isolated from Cd-hyperaccumulator Solanum nigrum L. grown in metal-polluted soil. Their plant growth promoting properties such as production of 1-aminocyclopropane-1-carboxylic (ACC) deaminase, indole-3-acetic acid (IAA), siderophores and phosphate solubilizing activity were characterized in vitro. When added to the Cd-amended soils, all of these four bacteria significantly increased Cd extraction from the soils. Subsequently, a pot experiment was conducted to elucidate the effects of inoculating of these PGPE on the plant growth and Cd uptake by S. nigrum L. grown in three different levels of Cd-contaminated soils. Results showed that the inoculation with these PGPE not only stimulated the growth of host plant, but also influenced the accumulation of Cd in the root, stem and leaf tissue of S. nigrum L. All four strains could colonize the rhizosphere soil and even some can be found in plant interior tissues. The present observations demonstrated that PGPE were valuable microorganism resource which can be exploited to improve the efficiency of phytoextraction.     

Arthrobacter sp. AG1菌株降解土壤中阿特拉津研究

在阿特拉津浓度为50mg/kg干土的黄棕壤、潮土和红壤接种1.5×106CFU/g干土的降解菌Arthrobacter sp. AG1,10天后土壤中的阿特拉津分别降解至1.5、6.6和10mg/kg干土。阿特拉津的降解速率受到土壤性质的影响,但AG1仍能在不满足其生长繁殖要求的pH值的土壤中有效降解酸性土壤中阿特拉津;土壤中水分含量对降解效果影响较大,>20%时降解效果较好;土壤低含水量和低pH值会导致AG1降解阿特拉津的活力下降。不同的接种量对降解效果有一定影响,但105～107CFU/g干土接种量的AG1都能有效发挥降解作用。AG1降解完土壤中的阿特拉津后,在土壤含水量分别为5%和15%的情况下能长期保持降解活性,对60天后第2次施入黄棕壤和潮土中的50mg/kg阿特拉津4天时降解效率在65%以上。     

Insecticidal activity of rhamnolipid isolated from pseudomonas sp. EP-3 against green peach aphid (Myzus persicae)

Microorganisms capable of growth on oils are potential sources of biopesticides, as they produce complex molecules such as biosurfactants and lipopeptides. These molecules have antimicrobial activity against plant pathogens, but few data are available on their insecticidal activity. The present study describes the insecticidal activity of a rhamnolipid isolated from diesel oil-degrading Pseudomonas sp. EP-3 (EP-3). The treatment of cell-free supernatants of EP-3 grown on glucose-mineral medium for 96 h led to > 80% mortality of aphids (Myzus persicae) within 24 h. Bioassay-guided chromatography coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MADLDI-TOF MS) and (1H, 13C) nuclear magnetic resonance (NMR) analyses was employed to isolate and identify the EP-3 insecticidal metabolites. Dirhamnolipid, with molecular formulas of C??H??O?? and C??H??O??, was identified as a main metabolite exhibiting insecticidal activity against aphids. Dirhamnolipid showed a dose-dependent mortality against aphids, producing about 50% mortality at 40 μg/mL and 100% mortality at 100 μg/mL. Microscopy analyses of aphids treated with dirhamnolipid revealed that dirhamnolipid caused insect death by affecting cuticle membranes. This is the first report of rhamnolipid as an insecticidal metabolite against M. persicae. Rhamnolipid shows potential for use as a pesticide to control agricultural pests.     

芽孢杆菌生物合成纳米硒条件优化及活性评价

作为生防菌的枯草芽孢杆菌XP（Bacillus subtilis subspecies stercoris strain XP）不仅具有较强的耐硒与耐盐能力,而且还可将毒性较高的无机硒转化为安全性高、生物活性好的纳米硒 (SeNP),然而目前其合成SeNP的效率并不高。为提升菌株XP生物合成SeNP的效率,该研究针对其合成工艺条件做了进一步优化。首先,通过单因素试验,初步筛选出适宜范围量值的初始亚硒酸盐Se (IV)浓度、摇床转速、XP接种量;其次,将这三个因子作为影响因素,以SeNP产量为响应指标,利用Box-Behnken响应面法 (RSM) 进行分析;最终,通过响应面法获得枯草芽孢杆菌XP产SeNP的最优发酵工艺条件。研究结果表明,枯草芽孢杆菌XP合成纳米硒的最佳发酵条件为：初始Se (IV) 3.4 mmol/L、摇床转速157 r/min、菌株XP接种量9.9%,此发酵条件下纳米硒的产量达到1.82 mmol/L,相对优化前提升了60%以上。此外,通过种子发芽试验,进一步证明此工艺条件下合成的纳米硒具有较高的生物活性,可有效提升油麦菜种子活力,促进种子萌发。