SELENIUM: AN ESSENTIAL ELEMENT FOR GROWTH OF THE COASTAL MARINE DIATOM THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE)1,2

An obligate requirement for selenium is demonstrated in axenic culture of the coastal marine diatom Thalassiosira pseudonana (clone 3H) (Hust.) Hasle and Heimdal grown in artificial seawater medium. Selenium deficiency was characterized by a reduction in growth rate and eventually by a cessation of cell division. The addition of 10⁻¹⁰ M Na₂eO₃ to nutrient enriched artifical seawater resulted in excellent growth of T. pseudonana and only a slight inhibition of growth occurred at Na₂SeO₃ concentrations of 10⁻³ and 10_-2 M. By contrast, Na₂SeO₄ failed to support growth of T. pseudonana when supplied at concentrations less than 10⁻⁷ M and the growth rate at this concentration was only one quarter of the maximum growth rate. The addition of 10⁻³ and 10⁻² M Na₂SeO₄ to the culture medium was toxic and cell growth was completely inhibited. Eleven trace elements were tested for their ability to replace the selenium requirement by this alga and all were without effect. In selenium-deficient and selenium-starved cultures of T. pseudonana cell volume increased as much as 10-fold as a result of an increase in cell length (along the pervalvar axis) but cell width was constant. It is concluded that selenium is an indispensable element for the growth of T. pseudonana and it should be included as a nutrient enrichment to artificial seawater medium when culturing this alga.     

SELENIUM STIMULATES GROWTH OF MARINE MACROALGAE IN AXENIC CULTURE1

The marine brown alga Fucus spiralis L. and the red alga Goniotrichum alsidii (Zanard) increase their growth upon the, addition of SeO₃^2- or SeO₄^2- when cultivated axenically in the artificial seawater ASP6 F2. In the concentration range 1 · 10^?10-1 · 10^?7 M there are two optima, one at 3.3 · 10^?10 M and another at 3.3 · 10^?8 M. α-To-copherol, often administered together with selenium to mammals suffering from selenium deficiency, gives no additive effect with selenium, but α-tocopherol in the concentration range 1 × 10^?7-1 × 10^?6 M does influence the morphology of the Fucus plants. Organically bound selenium has no effect.     

Na_2SeO_4对蛹虫草子实体生长的影响

蛹虫草是一种药食两用真菌,具有与冬虫夏草相似的功能,且富硒能力较强。本研究通过大量的人工栽培试验,旨在探究不同浓度Na_2SeO_4对新疆本地蛹虫草子实体生长的影响。试验表明,质量浓度为20 mg/L的Na_2SeO_4对蛹虫草的生长不产生显著影响,但蛹虫草各项生物学指标均随着培养基中外源Na_2SeO_4浓度的增加而呈下降趋势,说明随着外源Na_2SeO_4浓度的增加会对蛹虫草的生长产生抑制效应,当外源Na_2SeO_4质量浓度达到200 mg/L时,生产的蛹虫草已不具备商品价值。由此可见,20 mg/L的质量浓度是以Na_2SeO_4为硒源进行蛹虫草富硒研究的安全浓度。该研究为富硒产品开发寻找新的硒源开辟了新思路,为新疆地区进一步大规模栽培富硒蛹虫草提供一定的参考,但是对以Na_2SeO_4为硒源的最佳富硒浓度还有待于进一步研究。     

Specific Selenium-Containing Macromolecules in the Marine Diatom Thalassiosira pseudonana

Thalassiosira pseudonana Husedt (Hasle and Heimdal) clone 3H was grown in axenic culture in artificial seawater medium containing 10⁻⁸ molar Na₂⁷⁵SeO₃. Biochemical distribution of radiolabeled Se was determined by solvent extraction techniques, gel filtration, and polyacrylamide gel electrophoresis. Of the total cellular Se, 51% was protein bound. Two soluble macromolecules of 21 and 29 kilodaltons contained ⁷⁵Se. These results are the first to provide evidence of specific Se-containing compounds in a photosynthetic organism. Glutathione peroxidase (GSH-Px) activity was measured in cell-free extracts and on nondenaturing polyacrylamide gels by a glutathione-reductase coupled assay. Two enzymes showing GSH-Px activity were present. One enzyme was active with H₂O₂ and tert-butyl hydroperoxide (tBOOH); consistent with known Sedependent GSH-Pxs, but the other enzyme was only active with tBOOH. Co-migration of the H₂O₂-active GSH-Px and ⁷⁵Se on nondenaturing polyacrylamide gels provides evidence that T. pseudonana contains a Sedependent GSH-Px. The molecular weight of one of the ⁷⁵Se-labeled macromolecules is identical with the weight of previously characterized GSH-PX subunits. We conclude that the obligate requirement for Se in Thalassiosira pseudonana is due in part to the presence of the selenoenzyme glutathione peroxidase.     

The Effect of Selenite Ions on Growth and Selenium Accumulation in Spirulina platensis

Selenium accumulation and the growth of cyanobacterium Spirulina platensis (Nordst.) Geitl. were studied in a culture with sodium selenite-supplemented nutritional medium. Selenite concentrations below 20 mg/l did not inhibit the growth of S. platensis. The addition of 30 mg/l of this salt somewhat decreased the growth rate during the linear growth phase, induced the earlier suspension transition to the steady-state phase, and substantially lowered the highest optical density of the suspension. However, even at 170 mg/l Na₂SeO₃, the culture still demonstrated a capacity for growth. The content of selenium in the cells depended directly on its concentration in the medium, up to the lethal level. At high selenium concentrations (100–170 mg/l), S. platensis reduced Se(IV) up to Se(0). The latter was secreted onto the cell surface and into the cultural medium. The high concentrations of Na₂SeO₃ acidified the cytoplasmic pH as was measured by ³¹P-NMR spectroscopy. At the same time, the content of protein on a dry weight basis decreased and that of carbohydrates and lipids somewhat increased, just as was observed in S. platensis cells under other stress factors. In the presence of 20 mg/l Na₂SeO₃, the selenium content in the biomass increased by 20000 times as compared to that in the control cells, whereas the biochemical composition of biomass did not change. In this case, the selenium was incorporated almost completely in the protein fraction. The selenium concentration in this fraction increased more significantly when the sulfur content was lowered in the medium.     

Reactive oxygen species from mitochondria mediate SW480 cells apoptosis induced by Na2SeO3

A number of selenium compounds have been found to inhibit tumorigenesis in a variety of animal and cell models. In order to explore the molecular mechanism involved in the anticarcinogenesis activity of selenium, we examined the effects of sodium selenite on cell viabilty, generation of reactive oxygen species (ROS), and mitochondrial transmembrane potential (Δω _m ) in human colonic carcinoma cells SW480. The result from MTT test showed that sodium selenite reduced cell viability. Morophologic and flow cytometric results indicated that Na₂SeO₃ induced the apoptosis of SW480 cells. Na₂SeO₃ increased the generation of intracellular ROS, whereas BAPTA-AM, rotenone, and NaCN completely inhibited the increase of ROS induced by Na₂SeO₃. Na₂SeO₃ also caused the disruption of Δω _m . The intracellular ROS increase and apoptosis induced by Na₂SeO₃ were significantly decreased by superoxide dismutase (SOD), catalase. These data suggest that the ROS mediate apoptosis induced by Na₂SeO₃ and mitochondria may be a major source of Na₂SeO₃-induced ROS.     

Encapsulation of selenium in chitosan nanoparticles improves selenium availability and protects cells from selenium-induced DNA damage response

Selenium, an essential mineral, plays important roles in optimizing human health. Chitosan (CS) is an effective, naturally oriented material for synthesizing nanoparticles with preferable properties such as biocompatibility, biodegradation and resistance to certain enzymes. We have recently shown that cellular exposure to selenium compounds activates ataxia-telangiectasia mutated (ATM)-dependent DNA damage responses, a tumorigenesis barrier. To test whether nanoencapsulation of selenium modulates the cellular response to selenium compounds, the HCT 116 cancerous and the MRC-5 normal cells were treated with Na₂SeO₃ and methylseleninic acid (MSeA) encapsulated in CS/polyphosphate nanoparticles. Analyses of cellular selenium levels demonstrate that (1) the nanoencapsulation enhances selenium levels in cells after exposure to Na₂SeO₃ and MSeA (1-10 μM); (2) cells retained more selenium when treated with Na₂SeO₃ than with MSeA; (3) selenium levels are greater in HCT 116 than in MRC-5 cells after Na₂SeO₃, but not MSeA, exposure. Survival analysis shows that CS encapsulation desensitizes HCT 116 and MRC-5 cells to Na₂SeO₃ or MSeA exposure. Immunofluorescent analysis demonstrates that CS encapsulation attenuates the selenium-induced ATM phosphorylation on Ser-1981, and the extent is greater in HCT 116 than in MRC-5 cells. Our results reveal features of selenium nanoencapsulation in CS, including increased selenium retention in cells and decreased cellular sensitivity and DNA damage response to selenium exposure.     

Effect of different CO2 concentrations on biomass,pigment content,and lipid production of the marine diatom Thalassiosira pseudonana

The marine diatom Thalassiosira pseudonana grown under air (0.04% CO₂) and 1 and 5% CO₂ concentrations was evaluated to determine its potential for CO₂ mitigation coupled with biodiesel production. Results indicated that the diatom cultures grown at 1 and 5% CO₂ showed higher growth rates (1.14 and 1.29 div day⁻¹, respectively) and biomass productivities (44 and 48 mg_AFDWL⁻¹ day⁻¹) than air grown cultures (with 1.13 div day⁻¹ and 26 mg_AFDWL⁻¹ day⁻¹). The increase of CO₂ resulted in higher cell volume and pigment content per cell of T. pseudonana. Interestingly, lipid content doubled when air was enriched with 1–5% CO₂. Moreover, the analysis of the fatty acid composition of T. pseudonana revealed the predominance of monounsaturated acids (palmitoleic-16:1 and oleic-18:1) and a decrease of the saturated myristic acid-14:0 and polyunsaturated fatty acids under high CO₂ levels. These results suggested that T. pseudonana seems to be an ideal candidate for biodiesel production using flue gases.

     

Formate Dehydrogenase of Clostridium thermoaceticum: Incorporation of Selenium-75, and the Effects of Selenite, Molybdate, and Tungstate on the Enzyme

The formation of the nicotinamide adenine dinucleotide phosphate-dependent formate dehydrogenase in Clostridium thermoaceticum is stimulated by the presence of molybdate and selenite in the growth medium. The highest formate dehydrogenase activity was obtained with 2.5 × 10⁻⁴ M Na₂MoO₄ and 5 × 10⁻⁵ Na₂SeO₃. Tungstate but not vanadate could replace molybdate and stimulate the formation of formate dehydrogenase. Tungstate stimulated activity more than molybdate, and in combination with molybdate the stimulation of formation of formate dehydrogenase was additive. Formate dehydrogenase was isolated from cells grown in the presence of Na₂⁷⁵SeO₂, and a correlation was observed between bound ⁷⁵Se and enzyme activity.     

Arsenite-Induced Apoptosis Is Prevented by Selenite in A375 Cell Line

Arsenic trioxide induces apoptosis and clinical remission in patients diagnosed with acute promyelocytic leukemia. The human malignant melanoma A375 cells were treated with NaAsO₂ (0.1–130 μM) and also treated with combined 10 μM NaAsO₂ and 10 μM Na₂SeO₃. NaAsO₂ arrested cell growth in the G1 phase and induced apoptosis in a concentration- and time-dependent manner. In contrast, administration of Na₂SeO₃ antagonized the cell growth inhibition and apoptosis induced by NaAsO₂. The NaAsO₂ treatment resulted in a marked increase in p53 protein as early as 4 h and in Bcl-2 protein level by 12 h. In addition, p53 downregulation accompanied the combined treatment of NaAsO₂ and Na₂SeO₃. Thus, our results indicate upregulation of p53 and Bcl-2 play a crucial role in the NaAsO₂-induced G1 arrest and apoptosis of A375 cells and that downregulation p53 appears to contribute to the inhibition by Na₂SeO₃ of the effects induced by NaAsO₂.     

Selenium inhibition of avian fatty acid synthetase complex

Injection of 0.48 or 0.72 mg of selenium/100 g body weight (as Na₂SeO₃) into 3-week-old chicks depressed hepatic activity of fatty acid synthetase compared with saline-injected controls. In in vitro experiments with fatty acid synthetase purified to homogeneity, Na₂SeO₃ was a competitive inhibitor (K_i = ca. 70 μM). Dithiothreitol (DTT) at low concentrations increased the inhibition of the enzyme by Na₂SeO₃. At higher DTT concentrations the potentiating effect of DTT on selenium inhibition of the enzyme disappeared. At still higher DTT concentrations, selenium inhibition of fatty acid synthetase was partically relieved. If DTT and Na₂SeO₃ (2 : 1 molar ratio, respectively) in inhibitory concentrations, were reacted together prior to addition to enzyme and substrate, no inhibition was observed. Potentiation of selenium inhibition of fatty acid synthetase was observed with 2-mercaptoethanol but not with ascorbate. Several organic seleno-compounds were not inhibitory. The data suggest that selenium inhibits fatty acid synthetase by reversible bonding to the sulfhydryl (SH) groups (possibly at the active sites for acetyl-CoA and/or malonyl-CoA binding) of the enzyme. Selenotrisulfide formation involving selenium and the SH groups from the enzyme and thiol compounds is advanced as a possible explanation for the interaction among Se, DTT and enzyme observed in these experiments.     

TOXICITY OF COPPER TO THALASSIOSIRA PSEUDONANA IN UNENRICHED INSHORE SEAWATER1

Toxicity of copper to T. pseudonana (formerly Cyclotella nana, clone 13-1) wax examined in inshore seawater using a 96-hr bioassay method. Raw unenriched seawater wax filtered through a 0.22-μ membrane filter and then pasteurized, for 30 min at 60 C. Following this treatment, samples contained 0.68–1.14 μg Cu/liter. Copper was added as the chloride in 5-μg increments over the range of 5 to 30 μg/liter (about 0.1–0.5 μM). Population densities, mean cell, volume, and ¹⁴C bicarbonate uptake were measured. Population growth, and ¹⁴C uptake by T. pseudonana displayed inhibition over the entire range of added copper. Growth rate constant (k) of T. pseudonana decreased with increasing copper concentration and during the course of growth at each concentration. Correspondingly, mean cell volumes increased with copper concentration and time. Copper toxicity varied in different water samples. The presence of decomposed natural plankton and detritus decreased toxicity. In the absence of enrichment, bacteria had little effect on copper toxicity. H exults were influenced by glassware treatment, collection and storage of seawater, and absence of enrichments.     

Zinc-selenium interaction in the rat

Retention, dynamics of⁷⁵Se and⁶⁵Zn distribution, and elimination were studied in rats after separate or joint single doses of these metals. White female Wistar rats were divided into four groups (fifteen rats each). Group I received Na₂ ⁷⁵SeO₃ (0.1 mg Se/kg i.g.), group II received Na₂ ⁷⁵SeO₃+ZnCl₂ (5 mg Zn/kg s.c.), group III received⁶⁵ZnCl₂, and group IV received⁶⁵ZnCl₂+Na₂SeO₃. The zinc and selenium contents in the tissues were estimated during 120 h after administration; excretion in urine and feces of animals was determined throughout the experiment. Combined administration of zinc and selenium resulted in an enhanced selenium retention in the brain, spleen, kidneys, blood, lungs, and heart. A selenium-induced increase in the concentration of zinc was noted in the bowels, blood, liver, kidneys, spleen, brain, and lungs. The effects of the zinc/selenium interaction were visible especially in the lowered level of excretion of these elements. Zinc induced a decrease in the excretion of selenium in urine, with no concomitant changes in the excretion in feces. However, a visible decrease in the excretion of zinc in the feces was observed in the presence of selenium. The present results indicate an occurrence of clear-cut interaction effects between zinc and selenium administered simultaneously in the rat.     

INFLUENCE OF SALINITY ON THE FORM OF ASTEROCYTIS IN PURE CULTURE1

The growth form of an isolate of Asterocytis ornata in pure culture changed from filamentous in a full-strength seawater medium to a unicellular or bicellular form closely resembling the genus Chroothece in a medium of quarter-strength seawater. The alga did not grow in media of lower salinities, or in media in which seawater was replaced by KCl, NaCl, or CaCl₂. The formation of filaments from single cells could not be attributed to osmolarity. The controlling factors seemed to be the concentrations of cations, notably Na⁺ and Mg⁺⁺. However, the filaments produced experimentally in a defined medium, were never as extensively developed as those occurring in seawater, an indication that further studies should be done. The occurrence of the Asterocytis form, in freshwater habitats remains to be explained. There may be distinct physiological races, if not true species, within the genus.     

Effect of sodium selenite and methyl methanesulfonate or N-hydroxy-2-acetylaminofluorene co-exposure on sister-chromatid exchange production in human whole blood cultures

Sodium selenite (Na₂Se0₃) was tested for its sister-chromatid exchange (SCE)-inducing ability in human whole blood cultures and for the effect of its co-exposure with methyl methanesulfonate (MMS) or N-hydroxy-2-acetyl aminofluorene (N-OH-AAF) on SCE frequency. Long exposure times (77 h and 96 h) to 3.95 × 10^-6 M Na₂SeO₃ resulted in cell death as measured by mitotic indices, but mitotic figures were present after exposure to higher concentrations for a shorter time (19 h). High Na₂SeO₃ concentrations (7.90 × 10^?6 and 1.19 × 10^?5 M) resulted in a three-fold increase in the SCE frequency above background level (6–7 SCEs/cell). Exposure of lymphocytes to 1 × 10^?4 M MMS for the last 19 h of culture yielded an average SCE frequency of 30.17 ± 0.75 while a similar exposure to 2.7 × 10^?5 M N-OH-AAF resulted in 13.61 ± 0.43 SCEs/cell. Simultaneous addition of the high Na₂Se0₃ concentrations and MMS or N-OH-AAF to the cultures resulted in SCE frequencies that were 25–30% and 11–17%, respectively, below the sum of the SCE frequencies produced by the individual compounds.     

The effect of temperature and oxygen on the CO2 compensation point of the marine alga Ulva lactuca

Abstract The CO₂ compensation point of Ulva lactuca frond sections has been measured in artificial seawater using a sensitive gas-chromatographic method. Under nitrogen the compensation point remained relatively constant at 3–6 cm³ m⁻³ at temperatures from 10 to 30°C while in air-saturated medium (0.3 kg m⁻³ O₂) the compensation point rose from 5 cm³ m⁻³ at 10°C to 11 cm³ m⁻³ at 30°C. These responses of the compensation point to temperature and oxygen concentration indicate that there is little photorespiratory CO₂ loss in this marine macroalga, and the low values of these compensation points indicate that inorganic carbon is actively accumulated by the plant.     

The influence of selenium and caffeine on chemical carcinogenesis in rats,mutagenesis in bacteria,and unscheduled DNA synthesis in human lymphocytes

The influence of sodium selenite (Na₂SeO₃) and caffeine on chemical carcinogenesis induced in rats by diethylnitrosamine (DEN), N-nitrosomorpholine (NM), andN-methyl-N-nitro-N-nitrosoguanidine (MNNG) was investigated. A dose-dependent inhibitory effect of Na₂SeO₃ (l–10 ppm) on hepatocarcinogenesis induced by DEN was demonstrated. Na₂SeO₃ also increased the latency period for stomach tumor formation in rats treated with MNNG. Combined treatment of rats with Na₂SeO₃ plus vitamin C added to the diet resulted in a slight inhibition of NM-induced liver carcinogenesis. Supplementation of diet with Na₂SeO₃ plus butylated hydroxytoluene, vitamin C, and vitamin E did not reveal any additive inhibitory effect compared to the inhibitory effect of Na₂SeO₃ given alone. Caffeine (600 rag/L) reduced the number of liver tumors induced in rats by DEN. Preliminary experiments have indicated that combined treatment of rats with selenium and caffeine could result in more effective inhibition of DEN-induced liver carcinogenesis. Further experiments are being conducted to study the influence of selenium and caffeine on mutagenic activity of 1-methyl-l-nitrosourea (MNU) inSalmonella typhimurium TA 1535. The pretreatment of bacteria cells with Na₂SeO₃ (3–10 p.g/mL) increased the mutagenic response of bacteria to MNU. A synergistic stimulation of mutagenic activity of MNU was observed in bacteria pretreated simultaneously with Na₂SeO₃ and caffeine. In addition the influence of Na₂SeO₃ on UDS induced by DEN in human lymphocytes was investigated. The trace element inhibited the UDS up to 82%. The possible role of potentiation by NazSeO3 of the cell killing effect of DEN in inhibition of liver carcinogenesis was discussed.     

Uptake of nitrogen and production of kainic acid by laboratory culture of the red alga Digenea simplex

The red alga Digenea simplex was cultured with various culture media to clarify the nutritional conditions to produce kainic acid (KA ). Unlike the domoic acid‐producing red alga Chondria armata , D. simplex was insensitive to excessive manganese, and grew best (mean growth rate approximately 800% for 25 days) in modified PES medium (mPES ; seawater + nitrate, phosphate, iron, trace metals, vitamins, and 2‐[4‐(2‐hydroxyethyl)‐1‐piperazinyl]‐ ethanesulfonic acid) prepared with autoclaved seawater. Liquid chromatography‐mass spectrometry analysis of the algal extracts revealed that the KA content of the explants cultured with mPES or N·P·Fe medium (seawater + nitrate, phosphate, and iron) was somewhat higher than that of wild specimens (1748–2378 μg g^?1 vs 1562 μg g^?1). The ¹H‐nuclear magnetic resonance spectrum of the KA extracted and purified from pooled explants was indistinguishable from the previously reported KA spectrum. When D. simplex was cultured for 6 weeks with medium in which NaNO ₃ of mPES was replaced by Na¹⁵NO ₃, the ratio of ²¹⁴KA to total measured KA (^totalKA = ²¹³KA + ²¹⁴KA ) in the cultured explants (0.1 at the beginning of culture) gradually increased to 2.5, indicating that D. simplex produces KA in proportion to its growth under the condition in which sufficient nitrogen source is available.     

Effects of intraperitoneally‐administered vitamin E and selenium on the blood biochemical and haematological parameters in rats

The aim of this work was to determine the role of intraperitoneally‐administered vitamin E and selenium on the biochemical and haematological parameters in the blood of rats. Thirty‐two adult male Wistar rats were used in this study. All rats were randomly divided into four groups. The first group was used as the control. The second group was intraperitoneally administered with vitamin E (±‐α‐tocopheroryl acetate, 10 mg day⁻¹), the third group with Se (Na₂SeO₃ 0·2 mg over a day), and the fourth group with vitamin E and Se (vitamin E 10 mg + Na₂SeO₃ 0·2 mg over a day). This administration was done for 5 weeks. Blood samples were taken from animals at the end of the dosage period and biochemical parameters in serum samples and haematological parameters in total blood were determined. The levels of total cholesterol (p<0·01) and number of white blood cells (p<0·001) in blood were significantly higher in the vitamin E group than in the control group. The levels of ALP, total cholesterol (p<0·01) and number of white blood cells (p<0·01) in blood were significantly higher in the selenium group than in the controls. The levels of glucose (p<0·05), ALP (p<0·01), total cholesterol (p<0·001) and number of white blood cells (p<0·01) were higher in the vitamin E and selenium combined group than in the controls. Other parameters considered within this trial (ALT, LDH, creatinine, albumin, total protein, amylase, creatine kinase, HDL, triglycerides, total lipid, sodium, chloride, uric acids, red blood cell, haemoglobin, packed cell volume, MCV, MCH, MCHC) did not show statistically significant differences between the control and injected groups. The results indicated that blood glucose and total cholesterol levels, ALP activity and white blood cell counts were significantly increased by intraperitoneal administration of vitamin E and selenium in rats. Copyright © 1999 John Wiley & Sons, Ltd.