In situ bacterial selenate reduction in the agricultural drainage systems of western Nevada

Dissimilatory in situ selenate reduction to elemental selenium in sediments from irrigated agricultural drainage regions of western Nevada was measured at ambient Se oxyanion concentrations. Selenate reduction was rapid, with turnover rate constants ranging from 0.04 to 1.8 h-1 at total Se concentrations in pore water of 13 to 455 nM. Estimates of removal rates of selenium oxyanions were 14.38, and 155 mumol m-2 day-1 for South Lead Lake, Massie Slough, and Hunter Drain, respectively.     

Effect of Selenium on the Interaction Between Daunorubicin and Cardiac Myosin

The interactions between selenium (sodium selenite), anthracycline antibiotics daunorubicin (DNR), and major contractile protein cardiac myosin (CM) were investigated. The results showed that the binding force between selenium and CM was 100 times stronger than that of DNR and CM. There was no marked influence on fluorescence intensity of DNR-CM at selenium concentrations of up to 20 μM. The co-administration of selenium (0.5-10.0 μg Se/ml) together with DNR resulted in a significant reduction in mice cardiotoxicity. However, selenium at the dose of 50.0 or 100.0 μg Se/ml afforded no obvious protection. The data indicate that selenium in the form of sodium selenite at appropriate dosage (<10.0 μg Se/ml) diminish the cardiac toxicity of DNR, potentially allowing the use of DNR at higher dosages in clinical cancer chemotherapy.     

The organ distribution of selenium in German adults

The selenium concentrations were determined in liver, kidney, skeletal muscle, heart, brain, prostate, testis, bile, lung, and spleen of German traffic accident victims. In addition the nitrogen and phosphorus contents were determined in the same organs and tissues. On a per-weight unit basis, the highest selenium concentration was found in kidney. However, this corresponds to only 4% of the total body selenium. Most of the whole body selenium (50%) is present in skeletal muscle, which thus appears to act as a selenium storage organ. However, there is also evidence that selenium is required for muscle function. In plasma and interstitial fluid, .450 mg of Se, or 7.5% of the total body selenium is present. A comparison of the organ Se concentrations of the German traffic accident victims with the selenium concentrations of the same human organs as reported in different countries indicates that the organ concentrations of West Germans are comparable to that of the population of New Zealand, a low-Se country, and significantly lower than that observed in the organs of American, Canadian, and especially Japanese subjects. The international comparison of the organ selenium concentrations also revealed that the selenium uptake of kidney is higher at low- and adequate dietary Se intakes and lower if the dietary Se supply is high, as is the case for Japanese subjects. Estimates of the daily excretion of selenium with the bile indicate that the amounts are three times higher than the daily urinary losses and in the same order of magnitude as the daily dietary selenium intakes. Enterohepatic reabsorption of selenium from the bile appears to be a significant mechanism of conserving dietary selenium and to maintain Se balance at comparatively low dietary Se intakes.     

Simultaneous reduction of nitrate and selenate by cell suspensions of selenium-respiring bacteria.

Washed-cell suspensions of Sulfurospirillum barnesii reduced selenate [Se(VI)] when cells were cultured with nitrate, thiosulfate, arsenate, or fumarate as the electron acceptor. When the concentration of the electron donor was limiting, Se(VI) reduction in whole cells was approximately fourfold greater in Se(VI)-grown cells than was observed in nitrate-grown cells; correspondingly, nitrate reduction was approximately 11-fold higher in nitrate-grown cells than in Se(VI)-grown cells. However, a simultaneous reduction of nitrate and Se(VI) was observed in both cases. At nonlimiting electron donor concentrations, nitrate-grown cells suspended with equimolar nitrate and selenate achieved a complete reductive removal of nitrogen and selenium oxyanions, with the bulk of nitrate reduction preceding that of selenate reduction. Chloramphenicol did not inhibit these reductions. The Se(VI)-respiring haloalkaliphile Bacillus arsenicoselenatis gave similar results, but its Se(VI) reductase was not constitutive in nitrate-grown cells. No reduction of Se(VI) was noted for Bacillus selenitireducens, which respires selenite. The results of kinetic experiments with cell membrane preparations of S. barnesii suggest the presence of constitutive selenate and nitrate reduction, as well as an inducible, high-affinity nitrate reductase in nitrate-grown cells which also has a low affinity for selenate. The simultaneous reduction of micromolar Se(VI) in the presence of millimolar nitrate indicates that these organisms may have a functional use in bioremediating nitrate-rich, seleniferous agricultural wastewaters. Results with (75)Se-selenate tracer show that these organisms can lower ambient Se(VI) concentrations to levels in compliance with new regulations proposed for release of selenium oxyanions into the environment.     

Selenium in human nutrition: dietary intakes and effects of supplementation

The dietary selenium intakes of a young couple residing in Southern California were determined to be 107 and 99 micrograms/day for the husband and the wife, respectively, on the basis of a 30 day study. For other young adult Californians, the selenium intakes were estimated from 90 to 168 micrograms/day. The highest intakes were observed in individuals subsisting on diets rich in whole wheat grain cereal products and seafoods. The selenium concentrations in whole blood of the subjects under study correlated with the dietary selenium intakes directly (P less than 0.001). The administration of 150 micrograms of selenium/day in the form of commercially available supplements increases the blood selenium concentrations. After 3 weeks of supplementation, the selenium concentrations in whole blood of our subjects reached 0.21 micrograms/ml. Prolonged supplementation at higher Se dosage levels causes further increases of the blood concentrations: Two individuals who had been ingesting 350 and 600 micrograms/day for 18 months exhibited blood selenium levels of 0.35 and 0.62 micrograms/ml. The blood selenium concentration of all subjects declined slowly after cessation of supplementation. Selenium uptake from the supplements was not affected by the joint administration of zinc supplements at 15 mg zinc/day. Glutathione peroxidase blood levels did not correlate with blood Se concentrations.     

Selenium Deposition in Tissues and Eggs of Laying Hens Given Surplus of Selenium as Selenomethionine

Forty-eight Norwegian bred White Leghorn chickens were divided into 6 groups and fed a basal diet containing 0.30 mig Se/kg supplemented with 0, 0.1, 0.5, 1.0, 3.0 or 6.0 mg Se/ kg in the form of selenomethionine for 18 weeks. A supplement of only 0.1 mg Se/kg induced significantly higher selenium concentrations in breast muscle and eggs, particularly in the egg white. The increase of selenium in the tissue and egg was proportional to the amounts of selenomethionine added to the feed. In the group given 6.0 mg Se/kg, the selenium concentrations in all tissues and eggs analysed ranged from 4.8 to 7.3 μg Se/g. No signs of toxic effects were observed even at the highest intake of selenium. Excess supply of selenium as selenomethionine to chickens was shown to be more potent than sodium selenite in raising the selenium concentration in tissues and eggs. A supplementation up to 10 times the requirement did not increase the levels of selenium in poultry products to such a degree that they could be considered as a potential risk for human consumption.     

细菌还原氧化态硒产生红色单质硒的研究进展

硒是一种生命必需的微量元素,但高浓度时毒性较强且会造成环境污染。许多细菌可以将亚硒酸盐(SeO32-)或硒酸盐(SeO42-)等毒性较高的氧化态硒还原为毒性较小的红色单质硒(Se°),形成硒-蛋白复合物,它们对于获得最佳补硒方式和治理硒环境污染具有应用潜力。近年来,关于这一生物还原过程,人们进行了大量的研究,包括碳源、氧气、元素硫、谷胱甘肽以及一些氧化还原酶和膜转运蛋白等在内的多种物质都被发现可能影响或参与了细菌对硒的代谢。综述了细菌进行生物还原氧化态硒的影响因素及不同细菌产生红色单质硒机理的研究进展。     

The bioavailability of various selenium compounds to a marine wading bird

The uptake of dietary selenium (about 3.5 mg/kg AF dry wt) as selenomethionine, selenocystine, selenite, selenate, and fish selenium in the plasma and red blood cells (RBC) of the oystercatcher has been investigated. The birds received the various selenium compounds subsequently, for at least 9 wk. After dietary supplementation of selenocystine, selenite, and selenate, plasma selenium was about 350 μg/L and RBC selenium 2.1 mg/kg dry wt. After supplementation of selenomethionine, the plasma concentration increased to 630 μg/L, and the RBC concentration to 4.1 mg/kg dry wt. When the fodder contained 3.1 mg/kg fish Se, an average plasma and RBC concentration of 415 μg/L and 14.4 mg/kg dry wt, respectively, was measured. The maximal increase of the selenium concentration in the plasma was attained at first sampling, 14 d after a change in dietary selenium (selenomethione or fish Se); the uptake seemed to be a concentration-regulated process. RBC concentrations (γ in mg/kg dry wt) increased with time (X in d) according toY=a?be^?cX . Fifty percent of the total increase was attained within 17d, suggesting that diffusion into the RBC played a role. The selenium concentration in the plasma was positively correlated with the (fish) Se concentration in the fodder; the RBC concentration (60 d after the change in diet) was positively correlated with the plasma concentration. When the diet contained fish Se, the blood selenium concentrations of the captive birds were similar to the concentrations measured in field birds. Fish Se is a yet undetermined selenium compound. The present experiment showed that fish Se differed from selenomethionine, selenocystine, selenite, or selenate in uptake from the food and uptake in the RBC.     

Characterization of sediment bacteria involved in selenium reduction

Bacterial reduction of selenium (Se) oxyanions (Se[VI] and Se[IV]) to elemental Se (Se[0]) is one of the major biogeochemical processes removing Se from agricultural drainage water and depositing Se in the sediment. This study was conducted to characterize Se-reducing bacterial populations in Lost Hills evaporation pond sediment and to observe their response to Se(VI) and organic C amendments. Se(VI) was removed from the dissolved phase in the sediment slurries amended with organic C with a decrease in redox potential (Eh). Se(VI) concentrations decreased from 2137 to 79 microg L-1 after 9 days of incubation in a 5% soil slurry. Upon our screening process, 9 Se(VI)- and 14 Se(IV)-reducing bacteria were isolated from sediment slurries and identified by amplification and sequencing of 16S rDNA. Bacillus strains appeared to be dominant in the bacterial assemblages active in Se(VI) and Se(IV) reduction in the sediment. Halomonas pacifica and Staphylococcus warneri were also identified as Se(IV)-reducers. Indigenous bacteria have a significant role in the biogeochemical cycling of Se and may be stimulated by addition of a suitable organic source for Se reduction. The bacterial strains isolated from salt-affected and Se-contaminated Lost Hills evaporation pond sediment may have potential application in removing Se from high salt drainage water.     

Bioeffects of selenite on the growth of Spirulina platensis and its biotransformation

The bioeffects of selenium on the growth of Spirulina platensis and the selenium distribution were investigated. S. platensis was batch cultured in Zarrouk medium containing increasing concentrations of sodium selenite. The biotransformation characteristic of selenium was analysed by the determination of the detailed selenium distribution forms. At 35 degrees C, 315.2 microEm(-2) x s(-1), sodium selenite concentrations below 400 mg x l(-1) were found to stimulate algal growth, especially in the range of 0.5-40 mg x l(-1). However, above 500 mg x l(-1) sodium selenite was toxic to this alga with the toxicity being related to the sulfite level in the medium. S. platensis was found to resist higher selenite by reducing toxic Se(IV) to nonsoluble Se(0). Selenium was accumulated efficiently in S. platensis during cultivation with accumulated selenium increasing with selenite concentration in the medium. It was demonstrated that inorganic selenite could be transformed into organic forms through binding with protein, lipids and polysaccharides and other cell components. The organic selenium accounted for 85.1% of the total accumulated selenium and was comprised of 25.2% water-soluble protein-bound, 10.6% lipids-bound and 2.1% polysaccharides-bound selenium. Among the organic fractions lipid possessed the strongest ability to accumulate Se (6.47 mg x kg(-1)). The 14.9% inorganic selenium in S. platensis was composed of Se(IV) (13.7%) and Se(VI) (1.2%).     

Se(VI) reduction by continuous-flow reactors packed with Shigella fergusonii strain TB42616 immobilized by Ca2+-alginate gel beads

Selenium at high levels may cause adverse health effects on human beings and endanger aquatic lives due to its toxicity. Se(VI) reduction in continuous-flow reactors packed with Shigella fergusonii strain TB42616 immobilized by Ca²⁺-alginate gel beads was investigated under various hydraulic retention times (HRT) and influent Se(VI) concentrations. Removal efficiency up to 98.8 % was achieved after 96 days operation under an HRT of 5 days and an influent Se(VI) concentration of 400 mg/L. The results showed that the overall selenium removal efficiency was affected by the HRT and the bed height of the reactor but not the influent Se(VI) concentration. The steady-state data were analyzed using a mathematical model and Monod-type kinetics. Biokinetic parameters of half-velocity constants and maximum specific reduction rates were optimized using steady-state data obtained under a range of HRTs (0.73–5.0 days) at a constant influent Se(VI) concentration of 50 mg/L. The model was validated using steady-state data obtained under influent Se(VI) concentrations ranging from 10 to 400 mg/L while maintaining the HRT at 5.0 days. The high correlation coefficients between model calculated Se(VI) and Se(IV) concentrations and the experimental data indicate that the model is robust to predict the performance of the continuous-flow bioreactor.     

The effect of selenium and organic material in lake sediments on the bioaccumulation of methylmercury by Lumbriculus variegatus (oligochaeta)

The accumulation of methylmercury (MeHg) to an oligochaete worm Lumbriculus variegatus (Müller) was measured in two different lake sediments in the laboratory. ¹⁴C-labelled MeHg was added to sediments at the nominal concentration of 95 ng/g dw sediment. Groups of six oligochaete worms were exposed in glass beakers to 35 g of spiked sediment for 14 days. The two sediments had organic carbon concentrations of 3.4% and 9.9% and natural selenium concentrations of 1.45 and 0.28 mg/kg (dw), respectively. After two weeks exposure, both the accumulation rate of MeHg and the body residue in the worms were much lower in the sediment having a high organic carbon content. The effect of selenium concentration in the sediment on bioaccumulation of MeHg in Lumbriculus variegatus was measured in one sediment (organic carbon 3.4% and Se 1.45 mg/kg) by adding sodiumselenite (Na₂SeO₃) at different concentrations. The added amounts of selenium were 0, 0.1, 0.5, 2.5, 15.0, and 50.0 mg Se/kg dry sediment. In this exposure the nominal concentration of MeHg was 102 ng/g dw sediment. The two lowest selenium concentrations did not affect the bioaccumulation of MeHg. But, the dose of 2.5 mg Se/kg resulted in a 25% reduction in the body residue after two weeks exposure. When 15 and 50 mg Se/kg were added to the sediment the accumulation of MeHg in the organisms was decreased by 75% and 86%, respectively, as compared to the reference.     

Absorption, distribution, half-life and possible routes of elimination of dietary selenium in juvenile rainbow trout (Salmo gairdneri)

1. The influence of different levels of dietary selenium on the metabolism of selenium in rainbow trout was studied using 75Se as an indicator. 2. Gastric absorption of selenium by the trout appeared to be very efficient. 3. Highest tissue concentrations of selenium were noted in the liver and kidney. 4. Blood did not concentrate selenium and the plasma was the major transport medium. 5. The liver and kidney appeared to be involved in selenium excretion based on high tissue concentrations and variations in half-lives with selenium loading. 6. The biological half-life of selenium in the tissues decreased with increased selenium loading except in the liver, which at toxic dietary selenium concentrations became longer, suggesting a rate-limiting metabolic transformation of selenium for excretion in this organ.     

Selenium and sulfur accumulation and soil selenium dissipation in planting of four herbaceous plant species in soil contaminated with drainage sediment rich in both selenium and sulfur

Four selenium (Se) nonaccumulator plant species, including a forage grass species, Tall Fescue (Festuca arundinacea Schreb.), a forage legume species, Alfalfa (Medicago sativa L.), a wetland species, Rush (Juncus tenuis Wild.), and a dry-land alkaline soil species, Saltgrass (Distichlis spicata L.), were grown in soil contaminated by agricultural drainage sediment having elevated levels of Se and sulfur (S). The above-ground plant tissues were consecutively harvested five times and examined for Se and S accumulation. Plant tissue Se concentrations ranged from 23.0 mg kg-1 to 8.3 mg kg-1. Tissue S concentrations ranged from 3239 mg kg-1 to 7034 mg kg-1. Both tissue Se and S concentrations were significantly different between harvests, species, and species/harvest interactions. Total Se accumulation by the plant biomass harvested ranged from 0.3 to 1.3 mg per soil column and total S accumulations ranged from 87.5 to 321.1 mg per soil column. The reduction in the percentage of total soil Se after 24 weeks growth of the plant species ranged from 12.0% in the Tall Fescue planting to 17.3% in the Rush planting. Over 90% of the soil Se losses were unidentified losses and leaching of Se was prevented. The accumulations of Se and S in the plant biomass were very small compared with the total soil Se and S losses, but substantial amounts of total soil Se (12.0 to 15.0%) and S (28.0 to 50.9%) inventories were dissipated by the growing and harvesting of the plants. The soil S concentration was several hundred times higher than the soil Se concentration, but Se accumulation by the plants and Se dissipation from the soil were not impaired by the high level of soil sulfur. For natural grassland habitat restoration, such as at the Kesterson Wildlife Refuge in the Central Valley of California, or for restoration of large-scale Se contaminated agricultural lands, Se nonaccumulator plant species are favorable candidates, because the possibility of introducing Se toxicity into the food chain can be minimized.     

Simultaneous Reduction of Nitrate and Selenate by Cell Suspensions of Selenium-Respiring Bacteria

Washed-cell suspensions of Sulfurospirillum barnesii reduced selenate [Se(VI)] when cells were cultured with nitrate, thiosulfate, arsenate, or fumarate as the electron acceptor. When the concentration of the electron donor was limiting, Se(VI) reduction in whole cells was approximately fourfold greater in Se(VI)-grown cells than was observed in nitrate-grown cells; correspondingly, nitrate reduction was ~11-fold higher in nitrate-grown cells than in Se(VI)-grown cells. However, a simultaneous reduction of nitrate and Se(VI) was observed in both cases. At nonlimiting electron donor concentrations, nitrate-grown cells suspended with equimolar nitrate and selenate achieved a complete reductive removal of nitrogen and selenium oxyanions, with the bulk of nitrate reduction preceding that of selenate reduction. Chloramphenicol did not inhibit these reductions. The Se(VI)-respiring haloalkaliphile Bacillus arsenicoselenatis gave similar results, but its Se(VI) reductase was not constitutive in nitrate-grown cells. No reduction of Se(VI) was noted for Bacillus selenitireducens, which respires selenite. The results of kinetic experiments with cell membrane preparations of S. barnesii suggest the presence of constitutive selenate and nitrate reduction, as well as an inducible, high-affinity nitrate reductase in nitrate-grown cells which also has a low affinity for selenate. The simultaneous reduction of micromolar Se(VI) in the presence of millimolar nitrate indicates that these organisms may have a functional use in bioremediating nitrate-rich, seleniferous agricultural wastewaters. Results with ⁷⁵Se-selenate tracer show that these organisms can lower ambient Se(VI) concentrations to levels in compliance with new regulations proposed for release of selenium oxyanions into the environment.     

Deletion of selenoprotein P upregulates urinary selenium excretion and depresses whole-body selenium content

Deletion of the mouse selenoprotein P gene (Sepp1) lowers selenium concentrations in many tissues. We examined selenium homeostasis in Sepp1(-/-) and Sepp1(+/+) mice to assess the mechanism of this. The liver produces and exports selenoprotein P, which transports selenium to peripheral tissues, and urinary selenium metabolites, which regulate whole-body selenium. At intakes of selenium near the nutritional requirement, Sepp1(-/-) mice had whole-body selenium concentrations 72 to 75% of Sepp1(+/+) mice. Genotype did not affect dietary intake of selenium. Sepp1(-/-) mice excreted in their urine approximately 1.5 times more selenium in relation to their whole-body selenium than did Sepp1(+/+) mice. In addition, Sepp1(-/-) mice gavaged with (75)SeO(2-)(3) excreted 1.7 to 2.4 times as much of the (75)Se in the urine as did Sepp1(+/+) mice. These findings demonstrate that deletion of selenoprotein P raises urinary excretion of selenium. When urinary small-molecule (75)Se was injected intravenously into mice, over 90% of the (75)Se appeared in the urine within 24 h, regardless of selenium status. This shows that urinary selenium is dedicated to excretion and not to utilization by tissues. Our results indicate that deletion of selenoprotein P leads to increased urinary selenium excretion. We propose that the absence of selenoprotein P synthesis in the liver makes more selenium available for urinary metabolite synthesis, increasing loss of selenium from the organism and causing the decrease in whole-body selenium and some of the decreases observed in tissues of Sepp1(-/-) mice.     

Effect of in vitro selenium supplementation on bovine sperm motility

The effects of selenium (Se) on motility of bovine spermatozoa were evaluated in two experiments. In Experiment 1, increasing doses of Se alone or with vitamin E were found to increase motility in Se concentrations up to 1 mug/ml. However, Se alone had a greater effect than did Se with vitamin E. The sperm motility response to Se concentrations from background to 1 mug/ml on motility best fit a quadratic equation with a maximum at about .65 mug Se/ml. In Experiment 2, the effect of Se addition before and after freezing was evaluated. This experiment demonstrated that treatment of semen with Se before freezing significantly increased the post-thaw motility as compared with portions of the same ejaculate which were not treated. Treatment after thawing produced motilities which were intermediate and not significantly different from either pre-freezing supplementation or no supplementation at all. These data indicate that some semen exhibits a greater percentage of motile sperm when Se is added prior to freezing, however, no information is yet available on the fertility of Se-treated semen.     

Accumulation of selenium in a model freshwater microbial food web.

The transfer of selenium between bacteria and the ciliated protozoan, Paramecium putrinum, was examined in laboratory cultures. The population growth of the ciliate was not inhibited in the presence of the highest concentrations of dissolved selenite or selenate tested (10(3) micrograms liter-1). Experiments with radioactive 75selenite or 75selenate indicated that accumulation of selenium by ciliates through time was low when feeding and metabolism were reduced by incubating at 0 degrees C. However, selenium accumulated in ciliate biomass during incubation with dissolved 75Se and bacteria at 24 degrees C and also when bacteria prelabeled with 75Se were offered as food in the absence of dissolved selenium. When 75Se-labeled bacterial food was diluted by the addition of nonradioactive bacteria, the amount of selenite and selenate in ciliates decreased over time, indicating depuration by the ciliates. In longer-term (> 5-day) fed-batch incubations with 75selenite-labeled bacteria, the selenium concentration in ciliates equilibrated at approximately 1.4 micrograms of Se g (dry weight)-1. The selenium content of ciliates was similar to that of their bacterial food on a dry-weight basis. These data indicate that selenium uptake by this ciliate occurred primarily during feeding and that biomagnification of selenium did not occur in this simple food chain.     

Inhibitory effect of selenium on Cryptosporidium parvum infection in vitro and in vivo

The anticryptosporidial effect of sodium selenite (selenium) was evaluated in a bovine fallopian tube epithelial (BFTE) cell culture system and an immunosuppressed C57BL/6N adult mouse model. Parasite numbers in cell culture were significantly reduced (p<0.01) following treatment with selenium (Se) at concentrations of 6, 9, and 12 μM at 48 h postinoculation (PI) and at 1.5, 3, and 6 μM at 96 h PI. Parasite reduction was greater than 50% at 48 h PI when 9 and 12 μM Se was used, and at 96 h PI when 6 μM Se was used. Such Se-induced reduction of Cryptosporidium parvum infection was significantly (p<0,0001) blocked when using free-radical scavengers such as mannitol (20 mM). A combined solution of mannitol (20 mM) and reduced glutathione (0.5 mM) enhanced the blockage to almost 100%. Adult C57BL/6N mice were immunosuppressed with dexamethasone phosphate administered ad libitum (16 μg/mL) in drinking water and inoculated with 10⁵ oocysts/mouse. Significantly fewer (p<0.001) oocysts were shed in the feces of mice treated with Se administered ad libitum (12 μM) in drinking water than in untreated mice. The survival time of mice was also significantly increased (p<0.001) following Se treatment. Collectively, these results indicate that Se plays an important role in cryptosporidiosis, and oxidative stress caused by Se is probably a major mechanism in inhibition of C. parvum infection.