Metallomics approach to trace element analysis in ustilago maydis using cellular fractionation, atomic absorption spectrometry, and size exclusion chromatography with ICP-MS detection

Huitlacoche is the ethnic name of the young fruiting bodies of Ustilago maydis, a common parasite of maize. In Mexico and other Latin American countries, this fungus has been traditionally appreciated as a local delicacy. In this work a metallomics approach was used with the determination of eight elements in huitlacoche by electrothermal atomic absorption spectrometry as one facet of this approach. The results obtained indicated relatively lower concentrations of commonly analyzed metals, as referred to the data reported for other mushroom types. This effect was ascribed to different accessibilities of elements, depending on fungus substrate (lower from plant than from soil). Subcellular fractionation was accomplished by centrifugation of cell homogenates suspended in Tris-HCl buffer. Recoveries of the fractionation procedure were in the range of 71-103%. For six elements (Cr, Cu, Fe, Mn, Ni, and Pb), the mean relative contributions in cytosol, cell walls, and mixed membrane fraction were 50.7, 48.2, and 1.1% respectively. To attain the molecular weight distribution of compounds containing target elements as an additional aspect of the metallomics approach, the fungus extract (1% sodium dodecyl sulfate in Tris-HCl, 30 mmol L(-)(1), pH 7.0) was analyzed by size exclusion chromatography with UV and ICP-MS detection. With spectrophotometric detection (280 nm), the elution of high molecular weight compounds was observed in the form of one peak (MW > 10 kDa), and several lower peaks appeared at higher retention times (MW < 10 kDa). On ICP-MS chromatograms, a coelution of (59)Co, (63)Cu, (57)Fe, (202)Hg, (60)Ni, and (80)Se with the first peak on the UV chromatogram was clearly observed, indicating that a fraction of each element incorporated with high molecular weight compounds (12.7, 19.8, 33.7, 100, 19.4, and 45.8%, respectively, based on the peak area measurements). From a comparison of (80)Se and (33)S chromatograms (for sulfur analysis, the extract was obtained in the absence of SDS), both elements coeluted with the first UV peak, but their lower molecular weight compounds were apparently different. These findings may contribute to a better understanding of the accumulation of elements in mushrooms.     

Chemical characterization and anti-inflammatory effect of polysaccharides fractionated from submerge-cultured Antrodia camphorata mycelia

Five polysaccharide fractions (AC-1, AC-2, AC-3, AC-4, and AC-5) were obtained after systemic solvent extractions and precipitations from Antrodia camphorata mycelia with yields of 2.92, 10.38, 1.65, 0.34, and 1.64%, respectively. Gel permeation chromatography (GPC) analysis showed that the distribution of mean molecular mass of the fractionated polysaccharides was in the range of 394-940 kDa. The proximate compositions from each polysaccharide fraction revealed that all fractions belonged to the category of glycoprotein, having ratios of carbohydrate/protein ranging from 0.29 to 10.79 (w/w). Glucose or galactose was the major monosaccharide in all fractions except fraction AC-2, which has a mean molecular mass of 394 kDa with lyxose as the most prominent constituent. In the evaluation of the DPPH* radical scavenging capability, fraction AC-1 and AC-2 polysaccharides showed the better capabilities, around 74.5 and 50.5%, respectively, compared to the reference control of Trolox (87.5%) at a concentration of 1 microM. In testing with macrophage RAW264.7 cells, fraction AC-2 demonstrated a rather potent anti-inflammatory capability. Furthermore, the lipopolysaccharide-induced NO production and the protein expression by the inducible nitric oxide synthase (iNOS) gene were inhibited, respectively, in a dose-dependent (50-200 microg/mL) manner by fraction AC-2 polysaccharide.     

Evaluation of the inorganic selenium biotransformation in selenium-enriched yogurt by HPLC-ICP-MS

Selenium is an essential element in the human diet. Interestingly, there has been an increased consumption of dietary supplements containing this element in the form of either inorganic or organic compounds. The effect of using selenium as a dietary supplement in yogurt has been evaluated. For this purpose, different concentrations of inorganic Se (ranging from 0.2 to 5000 microg g(-1)) have been added to milk before the fermentation process. Biotransformation of inorganic Se into organic species has been carefully evaluated by ion-exchange, reversed-phase, or size-exclusion chromatography, coupled to inductively coupled plasma mass spectrometry (ICP-MS). Yogurt fermentation in the presence of up to 2 microg g(-1) of Se(IV) produces a complete incorporation of this element into proteins as has been demonstrated applying a dialysis procedure. Analysis by SEC-ICP-MS showed that most of them have a molecular mass in the range of 30-70 kDa. Species determination after enzymatic hydrolysis has allowed the identification of Se-cystine using two different chromatographic systems. The biotransformation process that takes place during yogurt fermentation is very attractive because yogurt can act as a source of selenium supplementation.     

Antioxidant capability of polysaccharides fractionated from submerge-cultured Agaricus blazei mycelia

Five polysaccharide fractions (AB-1, AB-2, AB-3, AB-4, and AB-5) were obtained after a systemic solvent extraction and precipitation of Agaricus blazei mycelia with yields of 5.20, 9.03, 2.84, 17.47, and 0.44%, respectively. Among which, AB-1 and AB-3 demonstrated great DPPH* radical scavenging ability around 85.0 and 72.0%, respectively, at a concentration of 5 mg/mL. The ferrous ion chelating powers were even more excellent at a concentration of 1 mg/mL, reaching almost over 99.65% for fractions AB-2, AB-3, and AB-4 as compared to the reference control of citric acid (35%); at a dosage of 5 mg/mL, fraction AB-1 even showed 105% in efficiency. In terms of the absolute chelating power (ACP), the mole numbers of ferrous (Fe2+) ions chelated were inversely related with the mean molecular mass of the polysaccharides in each fraction. In addition, gel permeation chromatography analysis showed that the more potent fractions were residing in those fractions with lower molecular masses, such as fractions AB-1 (757 kDa), AB-2 (887 kDa), and AB-4 (631 kDa) etc., and surprisingly, the free radical scavenging capability was also not closely correlated with the mean molecular masses, alternately being well-associated with the solubility of polysaccharides.     

Application of isotope dilution analysis for the evaluation of extraction conditions in the determination of total selenium and selenomethionine in yeast-based nutritional supplements

Isotope dilution analysis (IDA) has been used to quantify total selenium, total solubilized selenium, and the selenomethionine (SeMet) amount in yeast and yeast-based nutritional supplements after acid microwave digestion and different enzymatic extraction procedures. For this purpose, both a (77)Se-enriched SeMet spike, previously synthesized and characterized in our laboratory, and a (77)Se(VI) spike were used. In the analysis of the nutritional supplements, the SeMet spike was added to the sample and extracted under different conditions, and the (78)Se/(77)Se and (80)Se/(77)Se isotope ratios were measured as peak area ratios after high-performance liquid chromatography (HPLC) separation and inductively coupled plasma mass spectrometry (ICP-MS) detection. The formation of SeH(+) and mass discrimination were corrected using a natural SeMet standard injected every three samples. Similarly, total solubilized selenium was measured in the extracts after enzymatic hydrolysis using the (77)Se-enriched SeMet as a spike by direct nebulization without a chromatographic separation. To establish a mass balance, total selenium was also determined by IDA-ICP-MS on the yeast tablets after microwave digestion using (77)Se(VI) as a spike. Results showed that all enzymatic procedures tested were able to solubilize total selenium quantitatively from the solid. However, the recovery for the species SeMet, the major selenium compound detected, was seriously affected by the enzymatic procedure employed and also by the matrix composition of the supplement evaluated. For the yeast sample, SeMet recovery increased from 68 to 76% by the combined use of driselase and protease. For the nutritional supplements, the two most effective procedures appeared to be protease and driselase/protease, with a SeMet recovery ranging from 49 to 63%, depending upon the supplement evaluated. In the case of in vitro gastrointestinal enzymolysis, the results obtained showed 26-37% SeMet recovery, while the rest of selenium was solubilized as other unknown compounds (probably Se-containing peptides).     

Study of the role of the carbohydrate and protein moieties of soy soluble polysaccharides in their emulsifying properties

The objective of this work was to investigate the role played by the protein fraction of soy soluble polysaccharide (SSPS) during its adsorption at oil/water interfaces. SSPS was separated in a high (HMF; 310 kDa) and low (LMF; 20 kDa) molecular weight fraction by gel filtration. SSPS/HMF consisted of 91.6% carbohydrate and 2.2% protein and showed better emulsifying properties than those of the whole SSPS, whereas SSPS/LMF seemed to affect negatively the adsorption behavior of SSPS. SDS-PAGE of the protein fraction obtained from SSPS/HMF showed a molecular mass of 50 kDa, was composed predominantly of proline (23.1%) and glutamic acid (15.2%), and still contained 8.8% of neutral sugar and 5.3% of uronic acid. Results indicated that not all of the protein material present in SSPS contributes to SSPS functionality but that only the material associated with HMF aids in the adsorption of SSPS onto oil/water interfaces.     

Selenium species in aqueous extracts of alfalfa sprouts by two-dimensional liquid chromatography coupled to inductively coupled plasma mass spectrometry and electrospray mass spectrometry detection

The complementary use of two different liquid chromatographic mechanisms coupled to inductively coupled plasma mass spectrometry (ICP-MS) for selenium (Se) specific detection has permitted the screening of the most abundant Se-containing fractions in selenized alfalfa sprouts (Medicago sativa). Aqueous extracts of the sprouts were fractionated first by size exclusion chromatography (SEC) using a Superdex Peptide column and a mobile phase containing an ammonium acetate buffer (pH 7). Further purification of the individual SEC Se-containing fractions was carried out using two different chromatographic systems: a Shodex Ashaipack column, with a mixed mechanism of size exclusion and ion exchange, and a conventional reversed phase C8 using ion-pairing reagents. In both cases, the columns were coupled to an inductively coupled plasma mass spectrometer equipped with an octapole reaction system for Se specific detection. This system allowed the on-line monitoring of the most abundant Se isotopes (78Se, 80Se) by reducing the possible polytomic interferences affecting these ions by adding hydrogen (2 mL min(-1)) to the octapole reaction cell. The results obtained by both separation mechanisms were highly comparable, revealing the presence of Se-methionine and Se-methyl selenocysteine. Both compounds were then confirmed by analyzing the corresponding fractions by electrospray quadrupole-time-of-flight (ESI-Q-TOF) mass spectrometry. Finally, an additional Se-containing species showing Se isotope distribution was detected at a molecular ion m/z 239 in the ESI-Q-TOF. The collision-induced dissociation of the m/z 239 and 237 ions (corresponding to 80Se and 78Se isotopes, respectively) revealed the possible presence as well of a derivative of the Se-2-propenyl selenocysteine.     

Selenium-enriched sprouts. A raw material for fortified cereal-based diets

The selenium supply in almost all European countries, including Austria and Germany, is below the recommended daily intake. In these countries, selenium fortification of foods and the use of selenium supplements are quite popular to compensate for low Se intake from diets. In general, wheat (Triticum aestivum) is known to be a good source for bioavailable selenium, and many studies have been performed to enrich selenium in wheat by selenium fertilization of the soil. In the present work, the process of sprouting was investigated as an alternative to enrich selenium in wheat. Sprouting was chosen because it additionally improves the nutritional value of seeds, for example, by a higher vitamin content, a better quality of protein, and some other parameters. Wheat, alfalfa (Medicago sativa), and sunflower (Helianthus annuus) seeds were germinated for 5 and 7 days in solutions containing selenate. The selenium sensitivity of the sprouts was tested by measuring visible germination levels and seedling development. Uptake rates were studied by determination of total selenium using inductively coupled plasma mass spectrometry (ICP-MS). Metabolism of the absorbed selenium was analyzed by determination of selenium species in extracts of the sprouts using anion exchange HPLC coupled to ICP-MS. It was shown that sunflower sprouts were the most resistant and had the highest uptake rates (up to 900 mg/kg), but almost 100% of the selenium was extracted with water and found to be nonmetabolized selenate. Wheat and alfalfa were less resistant and enriched selenium up to concentrations of 100 and 150 mg of Se/kg of dry mass, respectively. The metabolism of the selenate was inversely related to the total uptake rates. At low Se enrichment (approximately 1-2 mg of Se/kg), <20% of the total selenium content within the sprouts remained as inorganic selenium, indicating a high metabolism rate. With increasing uptake the amount of selenate increased to approximately 40-50%. However, with the method used it is possible to produce sprouts containing certain amounts of selenium, which might provide substantial proportions of bioavailable selenium. In combination with the generally high nutritional value of sprouts, they might serve for production of improved cereal-based diets.     

Immunomodulatory properties of Grifola frondosa in submerged culture

Maitake (Grifola frondosa) is a popular mushroom in Asia for its tasty flavor and immune-stimulating property. The aim of the study is to investigate the innate immunity augmentation effects of different extracts of mycelia and culture filtrate from G. frondosa in submerged cultures. The hot water extract of mycelia showed the strongest cytokine induction effect as a function of its concentration in human whole blood culture. The most potent fractions of hot water extract, Fr. I and II, were mainly composed of polysaccharides with molecular masses of 43-140 and 13-38 kDa, respectively. These fractions (0.025 mg/mL) showed marked activity in enhancing phagocytosis of human polymorphonuclear neutrophils (PMN). In parallel, the expression of CD11b, an early marker of PMN activation, was also up-regulated dose dependently. This result suggested that complement receptor 3 was primed by these fractions. In addition to activation of phagocytes, these bioactive fractions also increased human peripheral blood natural killer cell cytotoxicity. These results imply that the relatively low molecular mass polysaccharides isolated from mycelia of G. frondosa can enhance innate immunity in vitro and therefore may serve as biological response modifiers.     

Multielemental speciation analysis of fungi porcini (Boletus edulis) mushroom by size exclusion liquid chromatography with sequential on-line UV-ICP-MS detection

An analytical methodology to determine the molecular weight (MW) distribution patterns of several elements among different compounds present in commonly consumed edible mushrooms is presented in this work. A hyphenated technique based on size exclusion liquid chromatography (SEC) coupled on-line to UV and inductively coupled plasma mass spectrometry (ICP-MS) detection was used. The association of the elements to high and low MW fractions was confirmed with sequential detection by UV and ICP-MS. Separation of the fractions was performed by injecting a 100 microL sample volume to a Superdex 75 column. The effect of different mobile phases on the separation was evaluated. Additionally, three different extraction conditions including 0.05 mol L(-1) NaOH, 0.05 mol L(-1) HCl, and hot water at 60 degrees C were applied to extract the elemental species from the mushroom samples. Significant differences were observed in the chromatograms depending on the extraction conditions utilized. Optimization of the experimental variables involved in the SEC-UV-ICP-MS coupling was carried out. The method was applied to investigate the fractionation patterns of Bi, Co, Cu, Fe, I, Mo, Ni, Se, and Zn in fungi porcini (Boletus edulis) mushroom. The results obtained in this work indicate an important association of most of the elements to high MW fractions.     

Effects of cooking on the cell walls (dietary fiber) of 'Scarlet Warren' winter squash ( Cucurbita maxima ) studied by polysaccharide linkage analysis and solid-state (13)C NMR

Cell wall polysaccharides of 'Scarlet Warren' winter squash ( Cucurbita maxima ) were investigated before and after thermal processing. Linkage analysis of polysaccharides was done by gas chromatography coupled to mass spectrometry (GC-MS). The linkage analysis showed the cell wall polysaccharide compositions of raw and cooked squash were similar. The total pectic polysaccharides (galacturonan, rhamnogalacturonan, arabinan, and arabinogalactan) contents of the cell walls of both raw and cooked squash were 39 mol %. The amounts of pectic polysaccharides and xyloglucan in the cell walls of squash showed little alteration on heating. The cellulose content of the raw and cooked cell walls was relatively high at 47 mol %, whereas the xyloglucan content was low at 4 mol %. Solid-state (13)C nuclear magnetic resonance (NMR) spectroscopy techniques were used to examine the molecular motion of the polysaccharides in the cell walls. The mobility of highly flexible galactan depends on the water content of the sample, but no difference was seen between raw and cooked samples. Likewise, the mobility of semimobile pectic polysaccharides was apparently unaltered by cooking. No change was detected in the rigid cellulose microfibrils on cooking.     

Mechanism of induced systemic resistance against anthracnose disease in cucumber by plant growth-promoting fungi

Plant growth-promoting fungi (PGPF) such as Phoma sp. (isolates GS8-1, GS8-2 and GS8-3) and non-sporulating fungus (isolate GU21-2) were tested for their ability to induce systemic resistance against Colletotrichum orbiculare in cucumber. These isolates, used as colonized barley kernels to natural soils, induced systemic resistance in the greenhouse as well as in the field. Different elicitors from PGPF such as cell walls retaining or lacking protein and lipids, cell walls lipid fraction, and three fractions of culture filtrate (CF) with different molecular weight ranges were tested for their ability to elicit the defense response of cucumber plants under controlled conditions. Cell wall fraction lacking protein and lipids and the cell wall lipid fraction from root colonizing isolates GS8-1, GS8-2, and GS8-3 protected plants against C. orbiculare. While, only cell wall lipid fraction and CF fractions of different molecular weight ranges of the isolate GU21-2 protected plants against C. orbiculare infection. Methanol-soluble substances from CF fractions with molecular weight greater than 12,000 and less than 8000 consistently protected plants against the pathogen. Germination of C. orbiculare spores decreased significantly at 72 h of incubation on leaves of PGPF-protected plants. Isolate GU21-2 was the most effective in inhibiting spore germination. On the other hand, isolates GS8-1 and GU21-2 induced lignifications in the hypocotyls of seven-day-old cucumber seedlings after challenge inoculation with C. orbiculare. Three-week-old cucumber plants treated with isolate GU21-2 and challenged with C. orbiculare showed increased activities of exo- and endo-forms of glucanase and chitinase, as well as peroxidase and polyphenol oxidase in the second true leaves. Induction treatment with isolate GS8-1 also increased the activities of these enzymes with the exception of exo-glucanase. This study shows that the inoculation of PGPF or its CF resulted in additive effect on the suppression of anthracnose disease in cucumber.     

Tissue-specific and developmental modifications of grape cell walls influence the adsorption of proanthocyanidins

Cell wall material from Vitis vinifera L. cv. Cabernet Sauvignon grape skin and flesh was isolated at different stages of grape maturity to determine whether developmental changes in cell wall composition in different tissue types influence the binding of proanthocyanidins (PAs). Trends in cell wall adsorption of, and selectivity for, PAs were determined using two skin PAs that differed in their average molecular masses. Flesh cell walls consistently bound a higher amount of PA than those from skin. Key structural differences that reduced PA adsorption in skin cell walls by comparison with flesh cell walls were endogenously higher concentrations of insoluble PA, Klason lignin, and lower cell wall-bound protein. These differences may confer reduced flexibility and porosity of skin cell walls relative to flesh cell walls. Analysis of skin and flesh cell wall properties revealed that the onset of ripening was associated with a loss of type I arabinogalactan and galacturonic acid, which indicated a degradation of pectin within the cell wall. Flesh cell walls consistently bound PAs of larger molecular mass, and changes in PA adsorption properties after the onset of ripening were minor. For skin cell walls, adsorption of PA was lowest immediately following solubilization of galacturonic acid, and high molecular mass PAs were poorly bound. As ripening progressed, PAs of higher molecular mass were selectively adsorbed by skin cell walls, which indicates that ongoing cell wall remodeling during ripening may confer an increased porosity within the skin cell wall matrix, resulting in a greater adsorption of PA within a permeable structure.     

Comparison of In Vitro PBET and Phosphoric Acid Extraction as an Approach to Estimate Selenite and Selenate Bioaccessibility from Soil

Several approaches have been used to estimate the bioaccessibility of trace metals from soils. Here, we applied phosphoric acid extraction and the in vitro test physiologically based extraction (PBET) to soils containing selenium (Se) and compared their performance in estimating the bioaccessibility of Se. For this purpose, we used two soil samples and two Certified Reference Material soil samples with a range of Se concentrations. The total Se contents were measured in the samples and in the extracts by hydride generation–atomic fluorescence spectroscopy. Moreover, we also measured selenite and selenate in the soil extracts (from phosphoric acid and from the PBET) using the coupled techniques liquid chromatography–UV photooxidation–atomic fluorescence spectroscopy and liquid chromatography–mass spectrometry with inductively coupled plasma. From the results obtained in the present study, the PBET showed that the selenium bioaccessible fraction was mainly attributed to the gastrointestinal step. When comparing the results from PBET with those of the phosphoric acid extraction, similar values of Se (IV) and Se (VI) were obtained for both extraction systems. An estimation of the bioaccessibility percentage of Se is also reported.     

东北平原土壤硒分布特征及影响因素

我国粮食主产区的东北平原一直被认为是严重缺硒或缺硒地方病经常发生的地区,地质大调查以来采用现代分析测试手段进行高精度土壤硒的富集、分布研究,对特色土地资源开发利用具有重要意义。以每4 km2 1个点的表层(0~20 cm)、每16 km21个点的深层(150~180 cm)土壤数据对东北平原土壤硒分布特征及影响因素进行统计分析。结果表明,东北平原表层土壤以足硒为主,足硒面积达51.54%,硒潜在不足面积占25.05%,Se反应不足面积仅为22.63%,富硒土壤面积不足1%;深层土壤则以缺硒为主,硒反应不足面积占80.68%。表层土壤Se含量相对于深层土壤表现出明显的富集特征,仅在西部盐碱化、沙化区及东部土壤发育程度低的基岩区为基本自然状态―弱富集特征,土壤硒继承成土母岩程度较弱,而铁锰氧化物、有机质、土壤类型、质地等理化性质对硒具有明显的富集作用,后期人类活动也是影响硒富集的主要因素,但表生富集作用、人类活动影响不足以使表层土壤达到富硒程度。     

Selenium and aflatoxin levels in raw Brazil nuts from the Amazon basin

Whereas selenium (Se) is an important antioxidant in human metabolism to prevent cancer, aflatoxins are highly carcinogenic. Brazil nuts from Eastern and Western Amazon regions were evaluated to find any relationship between Se and aflatoxins levels. A total of 80 (in-shell and shelled) nuts samples were collected directly from different forest sites and analyzed for Se by atomic emission spectrometry and aflatoxins by liquid chromatography tandem mass spectrometry. The limit of quantitation (LOQ) for Se was 2.0 mg/kg, and LOQ for total aflatoxins was 0.390 microg/kg. Nut Se levels from the Eastern region were higher than the Western, in addition to the aflatoxins. The moisture content (mc) and water activity (aw) of the raw nuts from the two regions did not present a significant difference, for either in-shell or shelled. The mc was 24.5% (minimum of 20.1% and maximum of 30.4%) and 22.1% (minimum of 14.6% and maximum of 28.9%) and a w of 0.85 for both regions. Further studies need to be carried out to discover the role of Se on fungi growth stress and aflatoxin production mechanisms.     

Olive fruit cell wall: degradation of pectic polysaccharides during ripening

Olive fruits at three stages of ripening (green, cherry, and black) have been studied. After cell wall isolation, the compositions of the cell wall and that of the phosphate-soluble polysaccharides were determined. In cell walls, decreases in arabinose, xylose, glucose, and uronic acid levels were observed, together with a slight increase in mannose on ripening. At the beginning of ripening, fragments of pectic polymers were the major constituents of the phosphate-soluble fraction, with the hemicellulosic ones increasing toward the end of the process. The molecular weight of the fragments solubilized was approximately 6 kDa. After cell wall fractionation, the pectic polysaccharides soluble in imidazole and sodium carbonate were also studied. In both fractions, between the green and cherry stages of ripening, a significant loss of homogalacturonans took place. Between the cherry and black stages of ripening, rhamnogalacturonan side chains were also released in addition to homogalacturonans. In any of the pectic fractions, changes in apparent molecular weight were quantified.     

Selenium Associations in Estuarine Sediments: Redox Effects

Selenium (Se) is a contaminant of concern in environments affected by discharges from smelting and coal-burning industries. Experiments hate been performed to investigate the phase associations of selenium in contaminated sediments under a range of controlled redox conditions. In this study, Se sediment associations were examined using the BCR sequential extraction technique after stabilisation at different redox states. It was shown that although most of the sediment-bound Se is associated with the operationally-defined “organic sulfide” fraction, as the measured redox potential of the system is increased. more Se moves into the “exchangeable” and “iron manganese oxy hydroxide” fractions. In these fractions. contaminants can be expected to be more bioavailable. As the mass of Se absorbed to sediments is typically at least an order of magnitude higher than the mass dissolved in porewaters. significant Se exposure may result from oxidative shifts in Se associations.     

Selenate reduction in river water by Citerobacter freundii isolated from a selenium-contaminated sediment

Bacterial reduction of selenate [Se(VI)] to insoluble elemental Se [Se(0)] is an important remedial technology to remove selenium (Se) from Se-impacted water. Citerobacter freundii, a Se(VI) reducer, isolated from a Se-contaminated sediment was assessed for its ability to reduce Se(VI) in a mineral culture medium and natural river water in a series of laboratory batch experiments. The results showed that a combination of yeast extract and glucose used in the culture medium was more effective than yeast extract alone, yeast extract plus sodium acetate, and yeast extract plus sodium lactate for reduction of Se(VI) to Se(0) by C. freundii. About 89-96% of the added Se(VI) (500-4500 microg/L) was reduced to Se(0) in the culture medium amended with 500 mg/L each of yeast extract and glucose. C. freundii can also survive in natural river water and reduce Se(VI). During an 8-day experiment in both sterile and nonsterile river water, 63-70 and 21-22% of the added Se(VI) was reduced to Se(0) and Se(-II), respectively. These results suggest that C. freundii has great potential for Se(VI) reduction and may be used for remediating Se-impacted water.     

Foliar application and uptake of selenium extracted from ryegrass

In a pot experiment a water extract from ryegrass (Lolium perenne) containing 21 mg/L selenium (Se) was sprayed on ryegrass, and the uptake of Se was compared with the uptake of Se applied as sodium selenite. The amount of Se recovered from the plants (0 to 53 mg/kg) was a linear function of the amount of Se applied (0 to 130 g/ha), both for the Se in the extract and for the sodium selenite. A total of 2.8 times more Se was recovered from the plants sprayed with the extract than from the plants sprayed with sodium selenite. When the plants were washed with Triton X‐100 the difference was still higher: from the ryegrass sprayed with the extract 5.3 times more Se was recovered from the grass sprayed with the extract than from the grass sprayed with sodium selenite.