The effect of vitamin E on the intracellular distribution of the different oxidation states of selenium in rat liver

1. The liver intracellular distribution of (75)Se, (75)Se(2-) and (75)SeO(3) (2-) formed from orally administered Na(2) (75)SeO(3) was studied in rats given four different dietary treatments. 2. Subcellular fractionation was done by using sucrose density gradients in a B XIV zonal centrifuge rotor, and conditions were established so that separation of lysosomal, mitochondrial, smooth- and rough-surfaced endoplasmic reticulum, and soluble fractions was achieved. 3. Marker enzymes acid phosphatase, succinate-2 - p - iodophenyl - 3 - p -nitrophenyl - 5 - phenyltetrazolium reductase and glucose 6-phosphatase were used, together with electron microscopy, to establish the identity of the fractions. 4. The dietary treatments investigated were: (a) vitamin E-deficient diet for 3 months, re-fed with vitamin E during the terminal 5 days; (b) vitamin E-deficient diet; (c) adequate diet; (d) vitamin E- and selenium-deficient diet, re-fed with vitamin E during the terminal 5 days. 5. In adequately fed rats, selenide was particularly associated with the mitochondrial fractions; in vitamin E-deficient rats, little selenide was found and the buoyant density of the mitochondria was increased, whereas re-feeding with vitamin E showed a restoration of the normal pattern. In vitamin E- and selenium-deficient rats, re-fed with vitamin E, there was no tendency for selenide to be localized in the mitochondria. 6. In the microsomal regions of the gradients, adequately fed rats showed a concentration of selenide, particularly in the smooth endoplasmic reticulum fractions, and to a lesser extent in the rough endoplasmic reticulum fractions. This was not observed in vitamin E-deficient rats, and the normal pattern was restored on re-feeding with vitamin E, both in rats given the vitamin E-deficient diet and the vitamin E- and selenium-deficient diet. 7. Some selenide was also found in the soluble fractions, when vitamin E was present, and a substantial proportion of this selenide was found to pass through a dialysis membrane. 8. These results are taken to support our hypothesis that the active form of selenium may be selenide located in non-haem iron-containing proteins, and that the function of vitamin E may be to protect the selenide from oxidation.     

Studies on selenium incorporation into, and electron-transfer function of, liver microsomal fractions from normal and vitamin E-deficient rats given phenobarbitone

1. The incorporation of ⁷⁵Se from Na₂⁷⁵SeO₃ into the liver endoplasmic reticulum of rats given phenobarbitone was investigated by using a zonal centrifuge technique. 2. It was found that, in rats deprived of vitamin E, or of vitamin E and selenium, phenobarbitone was without effect on the incorporation of ⁷⁵Se or on its conversion to ⁷⁵Se²⁻. When vitamin E was given at the same time as the phenobarbitone and ⁷⁵Se, there was a large increase in the amount of ⁷⁵Se and ⁷⁵Se²⁻ found in the smooth reticulum. It is concluded that there may be a specific vitamin E-dependent role for selenium and selenide in the smooth endoplasmic reticulum, and it is suggested, in the light of these and other observations, that the selenide may form a part of the active centre of a non-haem iron-containing protein `X', that may function in microsomal electron transport. 3. Measurements of the contents of cytochromes P-450 and b₅ in liver microsomal fractions of rats given vitamin E-deficient, and vitamin E- and selenium-deficient diets, showed that haemoprotein biosynthesis is unimpaired in these rats and phenobarbitone treatment resulted in the expected increase in the haemoproteins. 4. When the reduction of cytochrome P-450 by NADH and NADPH was measured, no difference was found between normal and deficient animals. 5. These results are discussed in relation to current knowledge of microsomal electron transfer.     

Incorporation of selenium from selenite and selenocystine into glutathione peroxidase in the isolated perfused rat liver

The erythrocyte-free, isolated perfused rat liver was used to study the incorporation of selenium into glutathione peroxidase. Gel filtration and ion exchange chromatography of liver supernatant demonstrated ⁷⁵Se incorporation into glutathione peroxidase. A 9-fold excess of unlabelled selenium as selenite or selenide very effectively reduced ⁷⁵Se incorporation from L[⁷⁵Se]-selenocystine, but a 100-fold excess of unlabelled selenium as selenocystine was relatively ineffective as compared to selenite or selenide in diluting ⁷⁵Se incorporation from [⁷⁵Se]selenite. These results indicate that selenide and selenite are more readily metabolized than is selenocysteine to the immediate selenium precursor used for glutathione peroxidase synthesis, and suggest a posttranslational modification at another amino acid residue, rather than direct incorporation of selenocysteine, as the mechanism for formation of the presumed selenocysteine moiety of the enzyme.     

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。     

Variation of glutathione level and synthesis activity in chick liver due to selenium and vitamin E deficiencies

Chicks were fed an amino acid mixture-based diet (basal diet) or one supplemented with selenium (Se, 0.2 micrograms/g as Na2SeO3) and/or vitamin E (100 micrograms/g as alpha-tocopherol). The group receiving the basal diet devoid of Se and vitamin E showed a tendency to grow slowly, but not significantly so, compared to the non-deficient control and manifested a symptom of exudative diathesis after the feeding period of 4 weeks. Supplementation of the basal diet with Se or vitamin E prevented the deficiency symptoms in the chicks. The hepatic GSH level and GSH synthesis activity were about three times as much in the Se- and vitamin E-deficient group as in the control. This was also the case for in vivo sulfur incorporation into hepatic GSH for 10 h post-injection with [35S]methionine. The increased level of GSH may partly compensate the hepatocytes for peroxidative damage.     

Glutathione peroxidase activity and chemical forms of selenium in tissues of rats given selenite or selenomethionine

Glutathione peroxidase (GPx) activity and deposition of selenium (Se) were examined in tissues of rats given dietary Se for 7 wk as either selenite or selenomethionine (SeMet) with 75Se radiotracer of the same chemical form. On the basis of Se:75Se ratio, all tissues of the rats fed selenite were equilibrated with the dietary source, but tissues of the SeMet fed animals maintained a ratio of Se:75Se greater than the dietary ratio. Deposition of dietary Se and 75Se was higher in most tissues of rats fed SeMet. Muscle 75Se was the largest single tissue pool of 75Se in both groups accounting for one-third of recovered 75Se in the rats fed selenite, and one-half of recovered 75Se in the rats fed SeMet. Tissue GPx activities were not different between the two dietary groups. The proportion of Se as GPx in tissues was highest in erythrocytes of the rats fed selenite (.81) and lowest in testes and epididymides of the rats fed SeMet (.009). The proportion of Se present in cytosolic GPx was consistently higher in tissues of rats fed selenite. Erythrocytes of the rats fed SeMet had more 75Se associated with hemoglobin, and muscle cytosols of the rats fed selenite had more 75Se associated with the G-protein. The proportion of 75Se as SeMet determined by ion exchange chromatography of tissue hydrolysates was higher in tissues of rats fed SeMet (highest in muscle and hemoglobin, 70%, and lowest in testes, 16%). In contrast, selenocysteine was the predominant form of Se present in tissues of rats given selenite. These results indicate that the form of Se administered will influence the form in the tissues, the percentage of Se with GPx and the body burden of Se.     

The nature of the acid-volatile selenium in the liver of the male rat

1. The properties of rat liver acid-volatile selenium have been compared with those of H(2)Se and (CH(3))(2)Se. 2. In model experiments oxidation-sensitive H(2) (75)Se was trapped quantitatively under anaerobic conditions in 0.1m-AgNO(3), and (CH(3))(2) (75)Se was trapped quantitatively in 8m-HNO(3). The acid-labile selenium of a liver homogenate, and of a microsomal fraction, was found to behave quite unlike (CH(3))(2) (75)Se and in a manner indistinguishable from H(2) (75)Se. 3. It was concluded that the acid-volatile material is certainly not (CH(3))(2)Se and that it is probably H(2)Se. 4. The significance of these findings is discussed in relation to current knowledge about the metabolism and detoxication of selenium, and a scheme is proposed which incorporates this knowledge with recent observations on the interactions between trace amounts of selenium and tocopherol, and the production of acute selenium deficiency by Ag(+) in vitamin E-deficient rats.     

Selenium is mobilized in vivo from free selenocysteine and is incorporated specifically into formate dehydrogenase H and tRNA nucleosides

Selenophosphate synthetase (SPS), the selD gene product from Escherichia coli, catalyzes the biosynthesis of monoselenophosphate, AMP, and orthophosphate in a 1:1:1 ratio from selenide and ATP. It was recently demonstrated that selenium delivered from selenocysteine by an E. coli NifS-like protein could replace free selenide in the in vitro SPS assay for selenophosphate formation (G. M. Lacourciere, H. Mihara, T. Kurihara, N. Esaki, and T. C. Stadtman, J. Biol. Chem. 275:23769-23773, 2000). During growth of E. coli in the presence of 0.1 microM (75)SeO(3)(2-) and increasing amounts of L-selenocysteine, a concomitant decrease in (75)Se incorporation into formate dehydrogenase H and nucleosides of bulk tRNA was observed. This is consistent with the mobilization of selenium from L-selenocysteine in vivo and its use in selenophosphate formation. The ability of E. coli to utilize selenocysteine as a selenium source for selenophosphate biosynthesis in vivo supports the participation of the NifS-like proteins in selenium metabolism.     

A comparison of the uptake of [75Se]selenite, [75Se]selenomethionine and [35S]methionine by tissues of ewes and lambs.

The fate of selenium, given as Na2(75)SeO3, or [75Se]selenomethionine, and of [35S]methionine administered intravenously to ewes and lambs, has been examined. The main intention was to follow the incorporation of selenium into protein in a number of tissues, including liver and kidney, and to measure the extent of that incorporation of selenoamino acid, particularly with respect to the administration of selenite. The ewes chosen were lactating ewes with lambs at foot, and the lambs were animals which had been weaned on to fodder low in selenium and were recovering from white muscle disease with selenium therapy. These two experimental situations were chosen as they offered conditions under which selenium incorporation might be considered to be maximal. Entry of isotope into milk was rapid and was greater when 75Se was given as the selenoamino acid than as selenite. In both ewes and lambs greater amounts of activity, derived from selenite, were bound to plasma proteins than to the proteins of milk. This was particularly evident in samples taken some hours after administration. This ability of the plasma to bind selenium was demonstrated by alkaline dialysis. Small, though significant amounts of selenium, derived from Na2(75)SeO3, were incorporated as selenoamino acids into the proteins of liver, kidney and pancreas, as well as into the proteins of milk and plasma. In ewes, both selenomethionine and selenocystine were identified chromatographically in enzyme digests of defatted liver and kidney. Some differences occurred in the distribution of labelled compounds in organs from lactating ewes and recovering lambs. The incorporation of selenium into protein is discussed briefly in relation to the recent findings of an association between selenium and the enzyme glutathione peroxidase.     

Effect of sodium selenosulfate on restoring activities of selenium-dependent enzymes and selenium retention compared with sodium selenite in vitro and in vivo

Sodium selenosulfate has been extensively used as a precursor of selenide ions in the preparation of nano Se-containing compounds. Its biological properties remain completely unknown. Sodium selenosulfate and sodium selenite were added to the medium of HepG2 cells and administered intraperitoneally at a dose of 0.1 mg Se/kg body weight to selenium-deficient mice, respectively. Both of the selenium compounds could increase the activities of glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) in a dose-dependent manner in cells and efficiently restore selenium retention and activities of GPx and TrxR in mice. All of the variables were in correlation with the Se supply. There was no distinction in elevating activities of GPx and TrxR between selenosulfate and selenite in vitro. After a 2-d supply of selenosulfate, the activity of GPx in the liver was 65% (p < 0.001) and Se accumulations in the liver, kidney and blood were 64%, 86%, and 65%, respectively, of those treated with selenite (allp < 0.01). With the 7-d selenosulfate supplementation, the activity of GPx in the kidney and activities of TrxR in the liver and kidney were 88%, 75%, and 78%, respectively, of those treated with selenite (allp < 0.01); Se retentions in the liver and kidney were 85% and 93%, respectively of those supplemented with selenite (bothp < 0.01). These facts indicated that selenosulfate could be absorbed and utilized in the biological system. No difference in vitro demonstrated that selenosulfate could be absorbed and generate reduced selenide as efficiently as selenite. The differences between the two compounds in vivo were the result of other factors that affected selenosulfate utilization in tissues.     

Vitamin E deficiency and vitamin C supplements: exercise and mitochondrial oxidation

The effects of dietary antioxidant vitamins E and C on exercise endurance capacity and mitochondrial oxidation were investigated in rats. The endurance capacity of both vitamin E-deficient and vitamin C-supplemented, E-deficient rats was significantly (P less than 0.05) lower (38.1 and 33.6%, respectively) than control animals. Compared with the normal and vitamin E-deficient rats, there was a significant (P less than 0.05) increase in the concentration of vitamin C in blood and liver of the vitamin E-deficient, C-supplemented animals. Hence dietary vitamin C supplementation does not prevent the inhibition of exercise endurance capacity or increased hemolysis seen in vitamin E deficiency. The mitochondrial activities for the oxidation of palmitoyl carnitine and alpha-ketoglutarate were significantly (P less than 0.05) decreased by a single bout of exercise in brown adipose tissue but not in muscle, heart, or liver from vitamin C-supplemented, E-deficient groups of rats when compared with the activities in the tissue from the same group of rats killed at rest. Similar results were also seen in brown adipose tissue from vitamin E-deficient rats. The results suggest a tissue-specific role for vitamins E and C in substrate oxidation and show that the poor endurance capacity of vitamin E-deficient rats cannot be attributed to any changes in the mitochondrial activity in skeletal or cardiac muscles. It is also concluded that vitamin C supplementation, at least at the dose employed in the present study, cannot counteract the detrimental effects associated with vitamin E deficiency.     

还原亚硒酸盐产生红色单质硒光合细菌菌株的筛选与鉴定

从实验室保藏的光合细菌中筛选出一株对亚硒酸钠还原效率较高的菌株S3,其亚硒酸钠还原产物通过透射电子显微镜及EDX(Electron-Dispersive X-ray)分析确定为红色单质硒。菌株S3的形态学特征、生理生化特征及光合色素扫描结果与固氮红细菌(Rhodobacter azotoformans)的特征基本一致;16S rDNA序列(GenBank登录号为DQ402051)在系统发育树中与固氮红细菌同属一个类群,序列同源性为99%。根据上述结果将菌株S3鉴定为固氮红细菌。初步研究了该菌株还原亚硒酸钠的特性,首次报道固氮红细菌具有还原亚硒酸盐产生红色单质硒的能力,为今后利用微生物方法治理环境中硒污染、利用微生物方法获得活性红色单质硒以及对微生物还原亚硒酸盐产生红色单质硒的机理研究奠定了良好的基础。     

A selenocysteine-containing selenium-transport protein in rat plasma

A selenocysteine-containing rat plasma protein (selenoprotein P) was examined for a possible role in the transport of selenium in the rat. A time-course study of the localization of injected 75Se from [75Se]selenite indicated that one-half of the selenium was sequestered by liver tissue 1 h after injection and that one-fourth of the 75Se in the plasma was attached to selenoprotein P 3 h after injections. By 25 h there was little 75Se in plasma, and much of the 75Se had accumulated in nonhepatic tissues. 75Se was incorporated into selenoprotein P by liver slices in a process that was sensitive to the protein synthesis inhibitor cycloheximide. The fate of 75Se from intracardially injected 75Se-labeled selenoprotein P was followed in rats maintained on selenium-deficient and selenium-sufficient diets. Substantially more of the injected 75Se was present per gram wet weight in the testes and kidneys than the livers of the selenium-deprived rats after 5 h. The results indicate that selenoprotein P is synthesized in rat liver and that it transfers selenium from the liver to extrahepatic tissues.     

Effects of intraperitoneally injected selenium and vitamin E in rats anesthetized with halothane.

Halothane, commonly used for anesthetizing humans and animals, is one of the most important volatile anesthetics and may cause the formation of free radicals during its biotransformation. Free radicals may lead to degeneration of liver cells. Vitamin E and glutathione peroxidase (GSH-Px) containing selenium are two natural antioxidants, and these may protect the cellular lipid and lipoproteins against oxidative damage caused by free radicals. Therefore, the purposes of the present study were to investigate the probable protective effects of intraperitoneally administered Se and vitamin E on liver enzymes and to determine some other hematological parameters in the halothane anesthesia of rats. All rats were randomly divided into five groups. The first group was used as a control, and physiological saline (0.9%) was intraperitoneally injected into these animals as a placebo. The second group was used as an anesthesia control group and was only anesthetized with halothane for two hours. The third group received intraperitoneally administered Se (Na2SeO3, 0.3 mg/200 g body weight), the fourth group vitamin E (dl-alpha-tocopheryl acetate, 100 mg/kg body weight), and the fifth group a Se plus vitamin E combination (Na2SeO3, 0.3 mg/200 g body weight + dl-alpha-tocopheryl acetate, 100 mg/kg body weight). The activities of aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase, triglycerides, erythrocyte counts, the packet-cell volume, hemoglobin concentrations and neutrophyle rates significantly increased (p < 0.05 to p < 0.01) after halothane anesthesia and returned to near control levels after Se, vitamin E and Se plus vitamin E injections. The values of cholesterol, total protein, white blood cell counts and lymphocyte rates significantly decreased (p < 0.05 to p < 0.01) in the anesthesia control group. However, the levels of albumin, total bilirubin, creatinine, the mean corpuscular volume, the mean corpuscular hemoglobin, and the mean corpuscular hemoglobin concentration were not statistically influenced. In conclusion, we have determined that halothane anesthesia affected some liver enzymes and some other biochemical and hematological parameters. Se, vitamin E and their combination may prevent the increase of liver enzymes after halothane anesthesia. Based upon these results, Se and vitamin E may play an important role in the indication of hepatic cellular injury produced by halothane.     

Estrogen status alters tissue distribution and metabolism of selenium in female rats

A reported association between estrogen and selenium status may be important in the regulation of selenium metabolism. In this study, the effect of estrogen status on the metabolism of orally administered (75)Se-selenite and tissue selenium status was investigated. Female Sprague-Dawley rats were bilaterally ovariectomized at 7 weeks of age and implanted with either a placebo pellet (OVX) or pellet containing estradiol (OVX+E2), or were sham operated (Sham). At 12 weeks of age, 60 μCi of (75)Se as selenite was orally administered to OVX and OVX+E2 rats. Blood and organs were collected 1, 3, 6 and 24 h after dosing. Estrogen status was associated with time-dependent differences in distribution of (75)Se in plasma, red blood cell (RBC), liver, heart, kidney, spleen, brain and thymus and incorporation of (75)Se into plasma selenoprotein P (Sepp1) and glutathione peroxidase (GPx). Estrogen treatment also significantly increased selenium concentration and GPx activity in plasma, liver and brain, selenium concentration in RBC and hepatic Sepp1 and GPx1 messenger RNA. These results suggest that estrogen status affects tissue distribution of selenium by modulating Sepp1, as this protein plays a central role in selenium transport.     

微生物硒代谢机制研究进展

硒(Se)是人与动物生命必需的微量元素,在医学保健和工业制造方面有着广泛的应用。硒在环境中有四种价态,包括硒酸盐Se O42-(+6)、亚硒酸盐Se O32-(+4)、单质硒Se0(0)和硒化物Se2-(-2)。微生物在硒的形态转化中扮演了重要的角色,影响着环境中硒的生物地球化学循环。本文主要从自然界中硒的循环以及微生物与硒代谢机制两个方面阐述微生物对硒的生物地球化学循环的重要性。     

High affinity selenium uptake in a keratinocyte model

The distribution of selenium in mammals has been recently shown to be mediated primarily by selenoprotein P. Even in the absence of selenoprotein P, selenium is distributed from the liver into all organs and tissues when supplemented in the diet. The form of selenium that is actively taken up by mammalian cells at trace concentrations has yet to be determined. We used a human keratinocyte model to determine whether reduction of the oxyanion selenite (SeO(3)(2-)) to the more reduced form of selenide (HSe(-)) would affect uptake. Indeed a reduced form of selenium, presumably selenide, was actively transported into keratinocytes and displayed saturation kinetics with an apparent K(m) of 279 nM. ATPase inhibitors blocked the uptake of selenide, as did the competing anions molybdate and chromate, but not sulfate. These results suggest that the small molecule form of selenium that is distributed in tissues is hydrogen selenide, despite its sensitivity to oxygen and reactivity to thiols.     

Effect of selenium deficiency and vitamin E deficiency on glutathione metabolism in isolated rat hepatocytes

Selenium deficiency and vitamin E deficiency both affect xenobiotic metabolism and toxicity. In addition, selenium deficiency causes changes in the activity of some glutathione-requiring enzymes. We have studied glutathione metabolism in isolated hepatocytes from selenium-deficient, vitamin E-deficient, and control rats. Cell viability, as measured by trypan blue exclusion, was comparable for all groups during the 5-h incubation. Freshly isolated hepatocytes had the same glutathione concentration regardless of diet group. During the incubation, however, the glutathione concentration in selenium-deficient hepatocytes rose to 1.4 times that in control hepatocytes. The selenium-deficient cells also released twice as much glutathione into the incubation medium as did the control cells. Total glutathione (intracellular plus extracellular) in the incubation flask increased from 47.7 +/- 8.9 to 152 +/- 16.5 nmol/10(6) selenium-deficient cells over 5 h compared with an increase from 46.7 +/- 7.1 to 92.0 +/- 17.4 nmol/10(6) control cells and from 47.7 +/- 11.7 to 79.5 +/- 24.9 nmol/10(6) vitamin E-deficient cells. This overall increase in glutathione concentration suggested that glutathione synthesis was accelerated by selenium deficiency. The activity of gamma-glutamylcysteine synthetase was twice as great in selenium-deficient liver supernatant (105,000 X g) as in vitamin E-deficient or control liver supernatant (105,000 X g). Hemoglobin-free perfused livers were used to determine the form of glutathione released and its route. Selenium-deficient livers released 4 times as much GSH into the caval perfusate as did control livers. Plasma glutathione concentration in selenium-deficient rats was found to be 2-fold that in control rats, suggesting that increased GSH synthesis and release is an in vivo phenomenon associated with selenium deficiency.     

Subcellular distribution of selenoproteins in the liver of the rat

After in vivo labeling with [75Se]selenite, the intracellular distribution of selenoproteins in the liver was investigated in selenium-adequate and selenium-deficient rats. In the subcellular fractions, which were obtained by differential centrifugation, the proteins were separated by means of SDS-PAGE and the selenium compounds were identified via their 75Se activity. In this way twelve selenium-containing proteins or protein subunits with molecular weights between 12,100 and 75,400 were found. Glutathione peroxidase was concentrated in the cytosol and in the mitochondria. With the newly detected selenoproteins, some were enriched in the cytosol, one was mainly found in the nuclear fraction and some, which were present mainly in the mitochondrial and microsomal fractions, are most probably membrane-bound. In the liver of selenium-depleted rats the selenium administered was used predominantly to restore the levels of some of the newly found selenoproteins, while in the liver of selenium-adequate animals most of the selenium retained was incorporated into the glutathione peroxidase. The differences in the distribution among the subcellular fractions and the specific incorporation of the element in selenium deficiency into certain compounds suggest that there are several metabolic pathways for selenium and that the selenoproteins are involved in several different processes of intracellular metabolism.     

Transformations of selenate and selenite by Stenotrophomonas maltophilia isolated from a seleniferous agricultural drainage pond sediment

A Gram-negative bacterium, identified as Stenotrophomonas maltophilia by fatty acid analysis and 16S rRNA sequencing, was isolated from a seleniferous agricultural evaporation pond sediment collected in the Tulare Lake Drainage District, California. In cultures exposed to the atmosphere, the organism reduces selenate (SeO4(2-)) and selenite (SeO3(2-)) to red amorphous elemental selenium (Se degrees ) only upon reaching stationary phase, when O2 levels are less than 0.1 mg l(-1). In 48 h, S. maltophilia removed 81.2% and 99.8% of added SeO4(2-) and SeO3(2-) (initial concentration of 0.5 mM), respectively, from solution. Anaerobic growth experiments revealed that the organism was incapable of using SeO4(2-), SeO3(2-), SO4(2-) or NO3- as a terminal electron acceptor. Transmission electron microscopy of cultures spiked with either Se oxyanion were found to contain spherical extracellular deposits. Analysis of the deposits by energy-dispersive X-ray spectroscopy revealed that they consist of Se. Furthermore, S. maltophilia was active in producing volatile alkylselenides when in the presence of SeO4(2-) and SeO3(2-). The volatile products were positively identified as dimethyl selenide (DMSe), dimethyl selenenyl sulphide (DMSeS) and dimethyl diselenide (DMDSe) by gas chromatography-mass spectrometry. Our findings suggest that this bacterium may contribute to the biogeochemical cycling of Se in seleniferous evaporation pond sediments and waters. This organism may also be potentially useful in a bioremediation scheme designed to treat seleniferous agricultural wastewater.