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Effect of selenium on lipid alternations in pigment-forming yeats
Abstract
The work deals with lipid modifications of pigment-forming yeasts Rhodotorula and Sporobolomyces growing under presence of selenium. This metal in the medium significantly prolonged lag-phase of all cultures and enlarged yeast cells. Total, neutral, and membrane yeast lipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol) consisted of predominantly palmitic, palmitoleic, stearic, oleic, linoleic, and linolenic acids. Selenium activated fatty acid unsaturation mainly in phosphatidylcholine due to elevated levels of linoleic and linolenic acids. Because biosynthesis of C18 unsaturated fatty acids in Rhodotorula and Sporobolomyces species may be associated with phosphatidylcholine moieties, selenium might be involved to the induction of membranebound fatty acid Δ12 and Δ15 desaturases in red yeasts. Oppositely, neutral lipids (primarily triacylglycerols) did not show such intensive changes in fatty acid composition as their polar counterparts. These observations could be applied for preparation of selenized red yeasts containing carotenoid pigments with enhanced accumulation of linoleic and linolenic acids.
... Various biotechnological strategies exist to optimize the bioconversion of inorganic selenium in culture media [21,[50][51][52]. These depend absolutely on the culture conditions (temperature, pH, nutrients, etc.), the microorganism used, and the concentrations of inorganic selenium in the experimental medium, since these all have a considerable impact on biomass [47], the intracellular selenium content [53], the amino acid and fatty acid profiles, and the pigments in the yeast [31,54]. In the present study, the nitrogen source that most favored selenium accumulation was ammonium chloride, primarily due to the absence of sulfur in the culture medium. ...
... Likewise, it has been described that fatty acid profiles in yeasts are affected by the presence of selenium in the culture medium. According to [54], red yeasts cultured in a medium supplemented with selenium (1.2 mM) produced a large amount of linoleic and linolenic acid. In yeasts of the genus Rhodotorula, selenium stimulates the biosynthesis of C18 fatty acids and promotes distribution in the membrane lipids [21]. ...
... Studies have demonstrated that selenium supplementation can increase unsaturated fatty acids in yeast biomass. Selenium has also been linked to the activation of fatty acid unsaturation, particularly in phosphatidylcholine, by raising the levels of linoleic and linolenic acids [48,54]. Research on yeast strains like Sporidiobolus and Saccharomyces cerevisiae has shown that under conditions of polyunsaturated fatty acid (PUFA) accumulation, there is a downregulation of components of the electron transport chain in mitochondria, an up-regulation of the pentose-phosphate pathway and fatty acid β-oxidation at the transcriptional level, and alterations in enzymatic antioxidants like catalase and glutathione-S-transferase [66]. ...
It is known that selenium (Se) is an essential trace element, important for the growth and other biological functions of fish. One of its most important functions is to contribute to the preservation of certain biological components, such as DNA, proteins, and lipids, providing protection against free radicals resulting from normal metabolism. The objective of this study was to evaluate and optimize selenium accumulation in the native yeast Rhodotorula mucilaginosa 6S. Sodium selenite was evaluated at different concentrations (5-10-15-20-30-40 mg/L). Similarly, the effects of different concentrations of nitrogen sources and pH on cell growth and selenium accumulation in the yeast were analyzed. Subsequently, the best cultivation conditions were scaled up to a 2 L reactor with constant aeration, and the proteome of the yeast cultured with and without sodium selenite was evaluated. The optimal conditions for biomass generation and selenium accumulation were found with ammonium chloride and pH 5.5. Incorporating sodium selenite (30 mg/L) during the exponential phase in the bioreactor after 72 h of cultivation resulted in 10 g/L of biomass, with 0.25 mg total Se/g biomass, composed of 25% proteins, 15% lipids, and 0.850 mg total carotenoids/g biomass. The analysis of the proteomes associated with yeast cultivation with and without selenium revealed a total of 1871 proteins. The results obtained showed that the dynamic changes in the proteome, in response to selenium in the experimental medium, are directly related to catalytic activity and oxidoreductase activity in the yeast. R. mucilaginosa 6S could be an alternative for the generation of selenium-rich biomass with a composition of other nutritional compounds also of interest in aquaculture, such as proteins, lipids, and pigments.
... Selenium (Se) is an essential metalloid element that plays a key role in the biosynthesis of important selenoenzymes, such as glutathione peroxidase, deiodinase iodothyronine, and thioredoxin reductase [1]. Though microorganisms can convert inorganic selenium into less toxic and more bio-available organic forms [2][3][4], variations in selenium content and availability cause differences in microbial growth and metabolic processes [5][6][7]. Recent studies have indicated that some fungi present metabolic mechanisms to tolerate Se, including those in lipid and amino acid metabolism [8,9]. For example, Xu et al. [10] reported that 200 mmol/L of Na 2 SeO 4 inhibits endophytic bacterial growth, though the endophyte Herbaspirillum sp. is capable of transforming Se through reduction. ...
... The profile of fatty acids is correlated with the duration of the cultivation period and selenium concentration [6]. C. utilis, without Se exposure, accumulated more oleic acid (C18:1), stearic acid (C18:0), palmitoleic acid (C16:1), and myristic acid (C14:0) than cultures treated with Se culture. ...
... However, Se supplementation promoted the abundances of oleic acid, palmitoleic acid, and myristic acid in S. cerevisiae [9]. Similarly, the addition of Se to the culture medium caused an increase in the C-18 fatty acid contents of S. cerevisiae [6]. Guan et al. [33] have found 90 µg/mL Se raised the concentration of arachidonic acid (C20:4) in Diasporangium jonesianum but reduced the levels of myristic acid, hexadecenoic acids (C16:1), and octadecenoic (C18:1), and slightly changed the level of other fatty acids when compared to the control group. ...
Selenium (Se) is not only an essential trace element critical for the proper functioning of an organism, but it is also an abiotic stressor that affects an organism’s growth and metabolite profile. In this study, Epichloë sp. from Festuca sinensis was exposed to increasing concentrations of Na2SeO3 (0, 0.1, and 0.2 mmol/L) in a liquid media for eight weeks. The mycelia and fermentation broth of Epichloë sp. were collected from four to eight weeks of cultivation. The mycelial biomass decreased in response to increased Se concentrations, and biomass accumulation peaked at week five. Using gas chromatography-mass spectrometry (GC-MS), approximately 157 and 197 metabolites were determined in the fermentation broth and mycelia, respectively. Diverse changes in extracellular and intracellular metabolites were observed in Epichloë sp. throughout the cultivation period in Se conditions. Some metabolites accumulated in the fermentation broth, while others decreased after different times of Se exposure compared to the control media. However, some metabolites were present at lower concentrations in the mycelia when cultivated with Se. The changes in metabolites under Se conditions were dynamic over the experimental period and were involved in amino acids, carbohydrates, organic acids, fatty acids, and nucleotides. Based on these results, we conclude that selenite concentrations and culture time influence the growth, extracellular and intracellular metabolite profiles of Epichloë sp. from F. sinensis.
... Worthy of mentioning is that the influence of Se in the microbial central metabolism has not yet been fully understood, while the effect of Se on the biochemical and physiological processes of oleaginous microorganisms is not yet explored. To the best of our knowledge, Čertík et al. [17] reported that a remodeling process of membrane lipid composition in red yeasts occurred, as a response to Se presence. ...
... The above resulted in 28% decrease of the U.I. in total lipids. On the contrary to our results, Čertík et al. [17] reported that the presence of Se increased FA unsaturation of total lipids in red yeasts. In addition, Pádrová et al. [57], reported that increased concentration of iron nanoparticles in the culture medium significantly decreased the amount of SFAs in the lipids of seven yeast strains, including Y. lipolytica. ...
... Probably, as Se influences a variety of metabolic processes, the available reducing power in the Se-enriched cells is insufficient to support FA elongation. Moreover, C18/C16 ratio reduced for both Y. lipolytica strains, on the contrary of results reported for red yeasts [17]. ...
Nowadays, there is an increase attention on the effect of selenium (Se) on metabolic processes of microorganisms. Strains
belonging to the genus of Yarrowia are of great biotechnological interest for various industries. In this study, we evaluated the
effect of 10 mg/L of Se on the growth and lipid production of two Yarrowia lipolytica strains: the ACA DC 50109 and one more
with increased oleagenicity, derived after ALE methodology (referred here as Y. lipolytica ALE_70). The presence of Se in the
growth medium negatively affected both cell mass production and total lipid accumulation, for both Y. lipolytica strains.
Fractionation of total lipids showed an inhibition on neutral lipid (NL) synthesis and consequently, an increase of polar lipids
(glycolipids plus sphingolipids, and phospholipids) on the lipids of the Se-enriched ACA DC 50109 strain; however, the NL/
polar ratio of the Se-enriched ALE_70 indicated that Se, apart from the inhibition of NL synthesis, provoked also the accumulation of polar lipids in this strain. In addition, the fatty acid (FA) composition was differently affected by Se. Se-enriched total
lipids of the ALE_70 strain were enriched in linoleic acid (C18:2 n-6), which resulted in increase of the unsaturated index. On the
other hand, Se-enriched lipids of the ACA DC 50109 strain were more saturated, as the percentage of palmitic (C16:0) and stearic
(C18:0) acids increased in the total FAs. Moreover, it seems that Se influenced the activity or the expression of desaturases and
elongase in both strains. Finally, the supplementation of growth medium with Se affected cell morphology, as well as the size and
distribution of lipid droplets inside the yeast cells. According to our opinion, Se caused stress conditions and the consequence of
that was the occurrence of metabolic disorders that affected cell mass, lipid content, and/or morphological structures. The results
of the present study suggest that further research should be carried out to understand the background of the lipogenesis process in
yeast cells cultured under stress conditions.
... Yeast can accumulate neutral lipids, which are stored in the form of liposomes (lipid droplets) [13]. Of note, the composition of lipids depends on both culture conditions and composition of the culture medium [14]. Thus, glycerolexhibiting a lipophilic structure-is transported through cytoplasmic membranes of yeast cells by simple diffusion and then, via metabolic reactions, it can be transformed into valuable products such as unsaturated fatty acids [15]. ...
... Large droplets of TAGs can occupy the larger part of a cell. The main fatty acid found in yeast lipids is oleic acid (C18:1), and its share can be even higher than 70% of total fatty acid [14,53]. The biomass of C. utilis yeast from the culture without added selenium was characterized by a significant amount of unsaturated fatty acids, including oleic acid (C18:1; 62%), linoleic acid (C18:2; 11%), and linolenic acid (18:3; 3%), in relation to the total fatty acid content (Fig. 6a). ...
... In the case of the other two acids, their increase was to approximately 42 and 57% of the total fatty acid content. According to reports by Čertík et al. [14], yeasts cultured in a medium supplemented with selenium (1.2 mM) produced large amounts of linoleic acid and linolenic acid. Moreover, selenium in Rhodotorula yeast stimulates the biosynthesis of C18 fatty acids, as well as promotes the distribution of unsaturated C18 fatty acids in membrane lipids. ...
This article discusses the effect of selenium in aqueous solutions on aspects of lipid and amino acid metabolism in the cell biomass of Saccharomyces cerevisiae MYA-2200 and Candida utilis ATCC 9950 yeasts. The yeast biomass was obtained by using waste products (potato wastewater and glycerol). Selenium, at a dose of 20 mg/L of aqueous solution, affected the differentiation of cellular morphology. Yeast enriched with selenium was characterized by a large functional diversity in terms of protein and amino acid content. The protein content in the biomass of S. cerevisiae enriched with selenium (42.6%) decreased slightly as compared to that in the control sample without additional selenium supplementation (48.4%). Moreover, yeasts of both strains enriched with selenium contained a large amount of glutamic acid, aspartic acid, lysine, and leucine. Analysis of fatty acid profiles in S. cerevisiae yeast supplemented with selenium showed an increase in the unsaturated fatty acid content (e.g., C18:1). The presence of margaric acid (C17:0) and hexadecanoic acid (C17:1) was found in the C. utilis biomass enriched with selenium, in contrast to that of S. cerevisiae. These results indicate that selenium may induce lipid peroxidation, which consequently affects the loss of integrity of the cytoplasmic membrane. Yeast enriched with selenium with optimal amino acid and lipid composition can be used to prepare a novel formula of dietary supplements, which can be applied directly to various diets for both humans and animals.
... Transesterification of the extracted lipid samples from the yeast cells cultivated in LAM supplemented with 1mM sodium selenite was performed as described by Van Wychen et al. [37] and briefly summarised by Elfeky et al. [6] to determine the fatty acid composition. An Agilent 7890B GC equipped with an autosampler and flame ionisation detector (FID) was used to analyse the fatty acid methyl ester. ...
... Our result was in agreement with a recent published paper, the authors found that the supplemintation of selenium in the culture media of the red pigmented yeast was signiffecantly enhanced the accumulation of unsaturated fatty acids especially oleic and linoleic acid. The authors suggested that the biosynthesis of C18 unsaturated fatty acids in Rhodotorula and Sporobolomyces species may be associated with phosphatidylcholine moieties, selenium might be involved to the induction of membrane bound fatty acid ∆12 and ∆15 desaturases in red yeasts [37]. ...
Background
Rhodotorula glutinis, a specific type of yeast, has been recognised as a superior resource for generating selenium-enriched biomass that possesses exceptional nutritional and functional attributes. The purpose of this investigation was to assess the effect of sodium selenite at different concentrations on lipid and carotenoid synthesis, as well as the growth of R. glutinis.
Methods
The lipid’s fatty acid composition was determined using gas chromatography (GC). The vitamins were detected by high-performance liquid chromatography (HPLC). Transmission electron microscopy was used to detect the structural modification of yeast cells caused by the addition of sodium selenite to the growth medium, as well as the accumulation of elemental selenium in the yeast cells.
Results
The yeast cells demonstrated the ability to endure high concentrations of sodium selenite under lipid accumulation (LAM) and growth-promoting (YPD) conditions. 25.0 mM and 30.0 mM, respectively, were published as the IC50 values for the LAM and YPD conditions. In both growth media, 1 mM sodium selenite boosted lipid synthesis. Lipid accumulation increased 26% in LAM to 11.4 g/l and 18% in YPD to 4.3 g/l. Adding 1 mM and 3 mM sodium selenite to YPD medium increased total and cellular carotenoids by 22.8% (646.7 µg/L and 32.12 µg/g) and 48.7% (783.3 µg/L and 36.43 µg/g), respectively. Palmitic acid was identified as the most abundant fatty acid in all treatments, followed by oleic acid and linoleic acid. The concentrations of water soluble vitamins (WSV) and fat soluble vitamins (FSV) were generally significantly increased after supplementation with 1.0 mM sodium selenite. TEM examination revealed a significant reduction in lipid bodies accumulation in the yeast cells when sodium selenite was added to lipid-promoting environments. This decline is accompanied by an augmentation in the formation of peroxisomes, indicating that selenium has a direct impact on the degradation of fatty acids. In addition, autophagy appears to be the primary mechanism by which selenium ions are detoxified. Additionally, intracellular organelles disintegrate, cytoplasmic vacuolization occurs, and the cell wall and plasma membrane rupture, resulting in the discharge of cytoplasmic contents, when a high concentration of sodium selenite (20.0 mM) is added. Also, the presence of numerous electron-dense granules suggests an intracellular selenium-detoxification pathway.
Conclusion
This study proposes the use of YPD with 1 mM sodium selenite to cultivate selenium-enriched biomass from R. glutinis. This approach leads to heightened lipid levels with higher accumulation of oleic, linoleic and linolenic acids, carotenoids, and vitamins. Hence, this biomass has the potential to be a valuable additive for animal, fish, and poultry feed. Furthermore, explain certain potential factors that indicate the impact of selenium in reducing the accumulation of lipid droplets in R. glutinis during lipogenesis, as detected through TEM examination.
... An association between selenium and fatty acids has been reported [46]. Kieliszek et al. [11] found that the main fatty acid in yeast was oleic acid (C18:1), and C. utilis without added selenium exhibited a high abundance of oleic acid (C18:1), stearic acid (C18:0), palmitoleic acid (C16:1), and myristic acid (C14:0), compared to the culture with selenium supplementation. ...
... However, selenium supplementation enhanced the levels of oleic acid, palmitoleic acid, and myristic acid in S. cerevisiae. Moreover, yeasts treated with selenium produced large amounts of linoleic acid and linolenic acid [46]. Under 90 μg/mL Se treatment, Guan et al. [47] reported elevated levels of arachidonic acid in Diasporangium jonesianum; however, the levels of myristic acid (14:0), hexadecenoic acids (16:1), and octadecenoic (18:1) were suppressed. ...
Selenium (Se) is an essential micronutrient with many beneficial effects for humans and other living organisms. Numerous microorganisms in culture systems enrich and convert inorganic selenium to organic selenium. In this study, Epichloë sp. from Festuca sinensis was exposed to increasing Na 2 SeO 3 concentrations (0, 0.1, 0.2, 0.3, and 0.4 mmol/L) in Petri dishes with potato dextrose agar (PDA) for 8 weeks. Epichloë sp. mycelia were immediately collected after mycelial diameters were measured at 4, 5, 6, 7, and 8 weeks of cultivation, respectively. Gas chromatography-mass spectrometer (GC-MS) analysis was performed on different groups of Epichloë sp. mycelia. Different changes were observed as Epichloë sp. was exposed to different selenite conditions and cultivation time. The colony diameter of Epichloë sp. decreased in response to increased selenite concentrations, whereas the inhibitory effects diminished over time. Seventy-two of the 203 identified metabolites did not differ significantly across selenite treatments within the same time point, while 82 compounds did not differ significantly between multiple time points of the same Se concentration. However, the relative levels of 122 metabolites increased the most under selenite conditions. Specifically, between the 4th and 8th weeks, there were increases in 2-keto-isovaleric acid, uridine, and maltose in selenite treatments compared to controls. Selenium increased glutathione levels and exhibited antioxidant properties in weeks 4, 5, and 7. Additionally, we observed that different doses of selenite could promote the production of carbohydrates such as isomaltose, cellobiose, and sucrose; fatty acids such as palmitoleic acid, palmitic acid, and stearic acid; and amino acids such as lysine and tyrosine in Epichloë sp. mycelia. Therefore, Epichloë sp. exposed to selenite stress may benefit from increased levels of some metabolite compounds.
... Besides, yeasts grown in YPG-Se medium presented higher lipid content. It is known that selenium can enhance lipid accumulation, mainly linoleic and linolenic acids in some yeasts [34]. In the study of Zhang et al. [35], the authors obtained 13.32 g/L of C. utilis biomass enriched with about 1000 ppm selenium after 18-h fermentation in YPD medium enriched with 15 mg/L Na 2 SeO 3 . ...
The use of agro-industrial by-products as feedstock for selenium-enriched yeast biomass production is an innovative and lowcost method. Thus, the present study aims for the utilization of sugarcane bagasse and corn bran hydrolysates for the production of selenium-enriched yeast and the evaluation of the effect of selenium in growth and cell composition. The hydrolysates were obtained using acid pretreatment, and yeasts were evaluated in different medium compositions. All evaluated yeasts were able to grow in the presence of 15 mg/L selenium. S. cerevisiae strains presented the major tolerance to selenium and better relation between selenium uptake and cell growth, with maximum cell biomass production of 7.97 ± 0.24 g/L and maximum selenium uptake of 1193 ± 336 ppm and 99% cell viability. Selenium also enhanced the lipid and protein concentration in cell extracts obtained after mechanical disruption. Regarding agro-industrial hydrolysates, corn bran hydrolysate allowed a better growth, with the production of 4.25 ± 0.49 g/L of biomass enriched with 167 ± 18 ppm selenium and 100% of viability. Starchy and lignocellulosic biomasses presented potential as low-cost alternatives for single-cell protein contributing to the development of sustainable and economically viable technologies.
... Besides, yeasts grown in YPG-Se medium presented higher lipid content. It is known that selenium can enhance lipid accumulation, mainly linoleic and linolenic acids in some yeasts [34]. In the study of Zhang et al. [35], the authors obtained 13.32 g/L of C. utilis biomass enriched with about 1000 ppm selenium after 18-h fermentation in YPD medium enriched with 15 mg/L Na 2 SeO 3 . ...
The use of agro-industrial by-products as feedstock for selenium-enriched yeast biomass production is an innovative and low-cost method. Thus, the present study aims for the utilization of sugarcane bagasse and corn bran hydrolysates for the production of selenium-enriched yeast and the evaluation of the effect of selenium in growth and cell composition. The hydrolysates were obtained using acid pretreatment, and yeasts were evaluated in different medium compositions. All evaluated yeasts were able to grow in the presence of 15 mg/L selenium. S. cerevisiae strains presented the major tolerance to selenium and better relation between selenium uptake and cell growth, with maximum cell biomass production of 7.97 ± 0.24 g/L and maximum selenium uptake of 1193 ± 336 ppm and 99% cell viability. Selenium also enhanced the lipid and protein concentration in cell extracts obtained after mechanical disruption. Regarding agro-industrial hydrolysates, corn bran hydrolysate allowed a better growth, with the production of 4.25 ± 0.49 g/L of biomass enriched with 167 ± 18 ppm selenium and 100% of viability. Starchy and lignocellulosic biomasses presented potential as low-cost alternatives for single-cell protein contributing to the development of sustainable and economically viable technologies.
Graphical abstract
... The obtained results demonstrate that bacteria may be used in bioremediating selenate-contaminated soils, sediments, and industrial wastes (Ridley et al. 2006; Sarret et al. 2005). Čertík et al. (2013) demonstrated that the addition of selenium to the culture medium caused a change in the fatty acid profile of the cytoplasmic membrane of yeast; they observed an increase in the content of C-18 fatty acids. On the other hand, in yeast enriched in carotenoids, they noticed a decomposition of unsaturated fatty acids (linoleic and linolenic acids). ...
This paper examines the process of selenium bioaccumulation and selenium metabolism in yeast cells. Yeast cells can bind elements in ionic from the environment and permanently integrate them into their cellular structure. Up to now, Saccharomyces cerevisiae, Candida utilis, and Yarrowia lipolytica yeasts have been used primarily in biotechnological studies to evaluate binding of minerals. Yeast cells are able to bind selenium in the form of both organic and inorganic compounds. The process of bioaccumulation of selenium by microorganisms occurs through two mechanisms: extracellular binding by ligands of membrane assembly and intracellular accumulation associated with the transport of ions across the cytoplasmic membrane into the cell interior. During intracellular metabolism of selenium, oxidation, reduction, methylation, and selenoprotein synthesis processes are involved, as exemplified by detoxification processes that allow yeasts to survive under culture conditions involving the elevated selenium concentrations which were observed. Selenium yeasts represent probably the best absorbed form of this element. In turn, in terms of wide application, the inclusion of yeast with accumulated selenium may aid in lessening selenium deficiency in a diet.
Selenium (Se) is a vital trace element, essential for growth and other biological functions in fish. Its significance lies in its role as a fundamental component of selenoproteins, which are crucial for optimal functioning of the organism. The inclusion of Se in the diets of farmed animals, including fish, has proved invaluable in mitigating the challenges arising from elemental deficiencies experienced in captivity conditions due to limitations in the content of fishmeal. Supplementing diets with Se enhances physiological responses, particularly mitigates the effects of the continuous presence of environmental stress factors. Organic Se has been shown to have higher absorption rates and a greater impact on bioavailability and overall health than inorganic forms. A characteristic feature of yeasts is their rapid proliferation and growth, marked by efficient mineral assimilation. Most of the selenized yeasts currently available in the market, and used predominantly in animal production and aquaculture, are based on Saccharomyces cerevisiae, which contains selenomethionine (Se-Met). The object of this review is to highlight the importance of selenized yeasts. In addition, it presents metabolic and productive aspects of other yeast genera that are important potential sources of organic selenium. Some yeast strains discussed produce metabolites of interest such as lipids, pigments, and amino acids, which could have applications in aquaculture and further enrich their usefulness.
Selenium (Se) is a vital trace element, essential for growth and other biological functions in fish. Its significance lies in its role as a fundamental component of selenoproteins, which are crucial for optimal functioning of the organism. The inclusion of Se in the diets of farmed animals, including fish, has proved invaluable in mitigating the challenges arising from elemental deficiencies experienced in captivity conditions due to limitations in the content of fishmeal. Supplementing diets with Se enhances physiological responses, particularly mitigates the effects of the continuous presence of environmental stress factors. Organic Se has been shown to have higher absorption rates and a greater impact on bioavailability and overall health than inorganic forms. A characteristic feature of yeasts is their rapid proliferation and growth, marked by efficient mineral assimilation. Most of the selenized yeasts currently available in the market, and used predominantly in animal production and aquaculture, are based on Saccharomyces cerevisiae, which contains selenomethionine (Se-Met). The object of this review is to highlight the importance of selenized yeasts. In addition, it presents metabolic and productive aspects of other yeast genera that are important potential sources of organic selenium. Some yeast strains discussed produce metabolites of interest such as lipids, pigments, and amino acids, which could have applications in aquaculture and further enrich their usefulness.
Selenium (Se) plays a critical role in diverse biological processes and is widely used across manufacturing industries. However, the contamination of Se oxyanions also poses a major public health concern. Microbial transformation is a promising approach to detoxify Se oxyanions and produce elemental selenium nanoparticles
(SeNPs) with versatile industrial potential. Yeast-like fungi are an important group of environmental microorganisms, but their mechanisms for Se oxyanions reduction remain unknown. In this study, we found that Aureobasidium melanogenum I15 can reduce 1.0 mM selenite by over 90% within 48 h and efficiently form intracellular or extracellular spherical SeNPs. Metabolomic and proteomic analyses disclosed that
A. melanogenum I15 evolves a complicated selenite reduction mechanism involving multiple metabolic pathways, including the glutathione/glutathione reductase pathway, the thioredoxin/thioredoxin reductase pathway, the siderophore-mediated pathway, and multiple oxidoreductase-mediated pathways. This study provides the first report on the mechanism of selenite reduction and SeNPs biogenesis in yeast-like fungi and paves an alternative avenue for the bioremediation of selenite contamination and the production of functional organic selenium compounds.
Selenium (Se) is a member of trace elements which are critical for proper functioning of an organism, and is one of the abiotic stressors which affect living organisms growth and metabolite. In this study, Epichloë sp. from Festuca sinensis was submitted to increasing Na 2 SeO 3 concentrations (0, 0.1, and 0.2 mmol/L) in the liquid media for 8 weeks. Epichloë sp. mycelia and fermentation broth were collected by centrifuging at 4, 5, 6, 7, 8 weeks of cultivation, respectively. About 157 and 198 metabolites were respectively determined in fermentation broth and mycelia using gas chromatography-mass spectrometer (GC-MS) analysis. Diverse changes in extracellular and intracellular metabolites were observed as Epichloë sp. exposured to selenite conditions and cultivation time. Eight common contributed metabolites (alanine, valine, isoleucine, glycine, serine, aminomalonic acid, 4-aminobutyric acid, and phenylalanine) were determined in fermentation broth and mycelia using principal component analysis (PCA). Some metabolites had highly accumulated in fermentation broth while others decreased after different time of exposure to Se as compared to the control media. However some metabolites were presented at lower concentrations in mycelia cultivated at selenite concentrations. These metabolites changed were involved in amino acids, carbohydrates, organic acids, fatty acids, and nucleotides under Se conditions, as well as ones over time. Based on these results, we conclude that selenite concentrations and culture time influenced the extracellular and intracellular metabolite profiles of Epichloë sp. from F. sinensis .
This study assessed the selenium (Se) removal efficiency of two pilot-scale high-rate algae ponds (HRAPs) treating domestic wastewater and investigated the production of Se-enriched microalgae as potential feed supplement. The HRAP-Se had an average Se, NH4⁺-N, total phosphorus and COD removal efficiency of, respectively, 43%, 93%, 77%, and 70%. Inorganic Se taken up by the microalgae was mainly (91%) transformed to selenoamino acids, and 49–63% of Se in the Se-enriched microalgae was bioaccessible for animals. The crude protein content (48%) of the microalgae was higher than that of soybeans, whereas the essential amino acid content was comparable. Selenium may induce the production of the polyunsaturated fatty acids omega-3 and omega-6 in microalgae. Overall, the production of Se-enriched microalgae in HRAPs may offer a promising alternative for upgrading low-value resources into high-value feed supplements, supporting the drive to a circular economy.
Monascus pigments (MPs) are widely used natural colorants in Asian countries. The problems of low extracellular red pigment (ERP) and high citrinin remain to be solved in Monascus pigment production. The effect of lanthanum(III) ion (LaCl3) on Monascus purpureus fermentation was investigated in this study. The yields of ERP and biomass respectively reached maxima of 124.10 U/mL and 33.10 g/L by adding 0.4 g/L La³⁺ on the second day in the total 8-day fermentation; simultaneously, citrinin was decreased by 59.93% and 38.14% in the extracellular and intracellular fractions, respectively. Reactive oxygen species (ROS) levels were obviously improved by La³⁺ treatment, while the activities of catalase (CAT) and superoxide dismutase (SOD) were increased compared with the control. The ratio of unsaturated/saturated fatty acids in mycelia was increased from 2.94 to 3.49, indicating that the permeability and fluidity of the cell membrane were enhanced under La³⁺ treatment. Gene expression analysis showed that the relative expression levels of Monascus pigment synthesis genes (pksPT, mppB, mppD, MpFasB2, and MpPKS5) were significantly upregulated by La³⁺ treatment, and in contrast, the relative expression levels of citrinin synthesis genes (ctnA, pksCT and mppC) were markedly downregulated. This work confirmed that LaCl3 possesses the potential to induce red pigment biosynthesis and inhibit citrinin production in M. purpureus fermentation.
Key points
• La³⁺induced red pigment and inhibited citrinin production in Monascus fermentation.
• La³⁺regulated genes expression up for Monascus pigment and down for citrinin.
• La³⁺increased the UFAs in cell membrane to enhance the permeability and fluidity.
Microbial oils enriched in essential polyunsaturated fatty acids can be used as nutritional complements. In order to improve the lipid yields and lipid profiles of 2 Yarrowia lipolytica strains, the effects of medium components and culture conditions were investigated using shake flasks. Under optimized conditions (cultivation for 3 days at 25oC and 150 rpm, using peptone as a nitrogen source and glucose as a carbon source), the biomass, lipid yield, and lipid content reached 6.75 g/L, 3.48 g/L, and 51.55% for Y. lipolytica QU22, and 6.85 g/L, 3.52 g/L, and 51.38% for Y. lipolytica QU137, respectively. Using a shaking speed of 150 rpm, unsaturated fatty acids constituted 87.96% (QU22) and 87.08% (QU137) of the total lipids produced by these strains, with 9.52 and 7.86% of alpha-linolenic acid, respectively. The strains are suitable candidates for fermentation processes involving essential polyunsaturated fatty acid (PUFA) production.
We evaluated selenium bioavailability from shrimps, and its effect on the metabolism of phospholipid (PL) and cholesterol ester (CE) using a mouse model. Experimental mice were categorized into 4 groups received different doses of Se from shrimps for 4 consecutive weeks. It was calculated that the bioavailability of Se from shrimps was ∼86–88% based on the apparent absorption. Comparing with control group, Se content in tissues and Glutathione peroxidase (GPx) activities in liver and blood increased significantly from selenium supplemented groups. The lipidomics analysis showed that there was no difference in detectable total species of PLs and CE in intestine samples, but the total content and the relative percentage of PLs and CE increased proportionally to the dose of Se intake. The results indicate that selenium supplementation lead to an increase in tissue Se concentration and GPx activity as well as changes in intestine PLs and CE, species and abundance of individual lipid fractions.
The tolerance, sorption of nickel(II) ions, and changes in the production and composition of exopolymers of eight yeast strains grown under nickel presence with/without NaCl were studied. Strains of Pichia anomala and Candida maltosa known as the most resistant yeasts against nickel tolerated up to 3 mM Ni2+. NaCl addition decreased both the resistance of the yeast strains toward nickel ions and the sorption of metal ions into cells. All yeasts absorbed nickel predominantly into exopolymers (glycoproteins) and on the surface of cells. However, while the amount of polysaccharide moieties of exoglycoproteins of most of the resistant yeasts was induced by stress conditions, the ratio polysaccharide/protein in the exopolymers remained unchanged in the sensitive species Cystofilobasidium. The exopolymer composition might play a key role in yeast adaptation to stress conditions caused by heavy metal ions.
Kinetic analysis of arachidonic acid (AA)-oil biosynthesis by Mortierella alpina 1S-4 growing under lipid-accumulating (LN medium) and non-lipid-accumulating (HN medium) conditions was investigated and compared with industrial AA fermentation. Various kinetic parameters of these cultivation processes demonstrate a characteristic pattern of the lipogenesis in this fungus, where growth phase, phase of oil accumulation and phase of AA synthesis are distinct from each other. The fungus utilizing LN medium synthesized 32.3 g fatty acid 100 g−1 glucose on the 4th day of cultivation and reached the maximum daily fatty acid accumulation (expressed as differential specific rate q
D(FA/B)) of 9.5%. Our results also indicate that a q
D(FA/B) value of about 2.5% might be critical for lipid overproduction in M. alpina. AA was rapidly incorporated into triacylglycerols (90% of total AA) at the later cultivation phase and overall AA yield was directly related to the total yield of fatty acid.
The main objective of this study was to evaluate the influence of diets enriched in individual conjugated linoleic acid (CLA) isomers, their mixture, and/or selenized yeast (Se-yeast) on the concentration of CLA isomers, long-chain polyunsaturated fatty acids (PUFA) and Se in the heart, muscles and liver of rats. The investigation was performed on 73 female Wistar rats (8 weeks of age, 200 g initial BW). After one week sub-maintenance feeding, rats received diets supplemented with 1% individual CLA isomers or 1 or 2% of a CLA isomers mixture, without or with 1.2 mg Se/kg (as Se-yeast) for 29 days. Feeding diets with 2% CLA isomer mixture reduced feed intake and body weight gain of rats, while addition of trans10,cis12 CLA and Se-yeast resulted in the highest body weight gain. CLA supplementation generally elevated the concentration of CLA isomers in heart and muscles significantly, although cis9,trans11 CLA accumulated preferentially. Regardless of the presence of Se-yeast, the dietary enrichment with CLA isomers caused a reduction in the capacity of A9-desaturase. Addition of Se-yeast to diets with individual CLA isomers or a 1% mixture of CLA isomers elevated the accumulation of CLA isomers in the heart and muscles, whereas all treatments with supplemented CLA and Se-yeast increased the accumulation of Se in rats compared with animals fed the diet containing Se only. Furthermore, CLA isomer supplementation decreased the concentration of PUFA and total fatty acids in the heart and muscles compared with control rats. Moreover, addition of CLA isomers interfered in the conversion of linoleic and linolenic acids to higher metabolites due to competition of CLA isomers for the same enzymes (delta6-, delta5-, delta4-desaturases and elongase).
Carotenoid-producing yeast species such as Rhodotorula glutinis and Sporobolomyces roseus efficiently accumulated selenium from the growth medium. It was observed that incorporation of selenium into yeast cells during the growth inhibited production of beta-carotenoid and other carotenoid precursors (torularhodin and torulene). The yeasts with high content of the carotenoid pigments and selenium may be used for the preparation of a new type of antioxidant formula that could be directly applied for various human and animal diets. We have demonstrated that such a formula can only be produced by separate processes of the cultivation of red yeasts and a subsequent sorption of selenium into the cells.
It has long been known that normal prokaryotic as well as eukaryotic cells can grow only when their membrane lipids are largely in the fluid state, i.e., at temperatures above the gel to liquid-crystalline transition temperature (T
m) of their membrane lipids (see McElhaney, this volume). Adaptation of bacteria (Cronan, 1975; Fulco, this volume), yeast (Watson, this volume), fungi (Miller and Barran, this volume), higher plants (Mazliak, 1979), and the protozoan Tetrahymena (Thompson and Nozawa, this volume) to temperatures below their normal growth temperatures generally results in changes in membrane lipid composition leading to increases in fatty acid unsaturation. The major factor affecting the fluidity of membrane lipids in eukaryotes, apart from the presence of cholesterol, is the degree of unsaturation of their fatty acid chains. This holds also for prokaryotes but, in addition, other factors such as chain length and branching may be important.
The objective of this study was to determine the distribution of total selenium (Se) and of the proportion of total Se comprised as the selenized amino acids selenomethionine (SeMet) and selenocysteine (SeCys) within the post mortem tissues of lambs that were fed high dose selenized enriched yeast (SY), derived from a specific strain of Saccharomyces cerevisae CNCM (Collection Nationale de Culture de Micro-organism) I-3060. Thirty two Texel X Suffolk lambs (6.87 ± 0.23 kg BW) were offered both reconstituted milk replacer and a pelleted diet, both of which had been either supplemented with high SY (6.30 ± 0.18 mg Se/kg DM) or unsupplemented (0.13 ± 0.01 mg Se/kg of DM), depending on treatment designation, for a continuous period of 91 d. At enrollment and 28, 56 and 91 d following enrollment lambs were blood sampled. At the completion of the treatment period, five lambs from each treatment group were euthanized and samples of heart, liver, kidney and skeletal muscle (longissimus dorsi and psoas major) were retained for Se analysis. The inclusion of high SY increased (P < 0.001) whole blood Se concentration, reaching a maximum mean value of 815.2 ± 19.1 ng Se/mL compared with 217.8 ± 9.1 ng Se/mL in control animals. Tissue total Se concentrations were significantly (P < 0.001) higher in SY supplemented animals than in controls irrespective of tissue type; values were 26, 16, 8 and 3 times higher in skeletal muscle, liver, heart and kidney tissue of HSY lambs when compared to controls. However, the distribution of total Se and the proportions of total Se comprised as either SeMet or SeCys differed between tissue types. Selenocysteine was the predominant selenized amino acid in glandular tissues, such the liver and kidney, irrespective of treatment, although absolute values were markedly higher in HSY lambs. Conversely selenomethionine was the predominant selenized amino acid in cardiac and skeletal muscle (longissimus dorsi, and psoas major) tissues in HSY animals, although the same trend was not apparent for control lambs in which SeCys was the predominant selenized amino acid. It was concluded that there were increases in both whole blood and tissue total Se concentrations as a result of dietary supplementation with high dose of SY. Furthermore, distribution of total Se and Se species differed between both treatment designation and tissue type.
A feeding experiment was carried out to compare the effects of supplementing a poultry meal-based diet with selenium as sodium selenite or selenium yeast on broiler chickens. Three groups with three replicates of broiler chickens (mean weight 710±5.3g) were given a basal diet either unsupplemented (control) or supplemented with 0.2mgSekg−1 as sodium selenite (trial 1) or selenium yeast (trial 2) respectively, for 21 days. There was significant difference (P0.05) in FCR between trials 1 and 2. Final weight, survival rate and Daily Gain (DG) were not affected by the dietary Se source. Chickens fed the basal diet showed lower (P
Thirty-two, 17 weeks old, wether lambs (Chinese Poll Dorset×Small Tailed Han×Charolais), weighing 26.3±1.2kg, were used to evaluate effects of different Se levels and polyunsaturated fatty acid (PUFA) sources in the diet on fatty acid composition and antioxidant status in plasma and liver. Lambs were divided into four groups and each was fed one of the following diets: 950g basal diet/kgDM and 50g linseed oil/kgDM (LO); LO plus 2mg Se/kgDM (as sodium selenite) (LOSe); 950g basal diet/kgDM and 50g sunflower oil/kgDM (SO); SO plus 2mg Se/kgDM (SOSe). The experiment lasted 50 days and lambs were slaughtered at the end of it. Concentrations of C18:2trans-10, cis-12 in liver, and C18:1trans-11 in plasma, increased with Se supplementation, which also increased concentrations of C20:4 in lambs fed the sunflower oil diet, but not in those fed the linseed oil diet, in both plasma and liver. Fatty acid composition in plasma and liver reflected the dietary fatty acid source. Lambs fed the linseed oil diet had higher concentrations of C18:3n-3, C20:5n-3 and C22:6n-3. In contrast, lambs fed the sunflower oil diet had higher concentrations of conjugated linoleic fatty acid, C18:2n-6 and C20:4n-6. Antioxidant status increased with Se supplementation, but was not affected by PUFA source in the diets. Results indicate the possibility of increasing the PUFA deposition by combining Se with PUFA in lamb diets, and that Se increased concentrations of C20:4n-6 more efficiently when combined with the sunflower oil diet versus the linseed oil diet.
Treatment of 19 vol of 10% solution of milk fat in petroleum ether with 1 vol of either 2 n methanolic potassium hydroxide or sodium methoxide at room temperature results in the almost instantaneous formation of methyl esters from glyceride fatty acids. The solution may be analyzed by gas chromatography at once.
Advances in analytical methodology for speciation of selenium in selenized-yeast food supplements were discussed on the basis of the recent developments in the authors’ laboratory. Particular attention was given to the sample preparation with regard to the fractionation of selenium into different classes of chemical species, the high resolution fractionation of selenium from yeast water extracts by size-exclusion chromatography and characterization of the water soluble protein fraction by combined matrix-assisted laser desorption ionization (MALDI)-time-of-flight mass spectrometry (TOF MS) and electrospray quadrupole-TOF tandem MS. The true speciation of protein-incorporated selenium (down to individual proteins characterized by a unique aminoacid sequence) was discussed using an example of a family of selenium-containing proteins formed in yeast by the substitution of methionine residues by selenomethionine in a salt stress-induced protein.
The effect of extraction procedures on the lipid yield and fatty acid composition of total lipid and main lipid structures
(phospholipids, diacylglycerols, triacylglycerols, free fatty acids, and sterol esters) of fungal biomass (Mucor mucedo CCF-1384) containing γ-linolenic acid (GLA) was investigated. Seventeen extraction methods, divided into three groups, were
tested: six with chloroform/methanol, five with hexane/alcohols, and six with common solvents or mixtures. The chloroform/methanol
procedure (2∶1) was selected as standard, where lipid yield (TL/DCW, total lipid per dry cell weight) was 17.8%, considered
to be 100% of lipids present. All chloroform/methanol extractions yielded more than 83% recorvey of lipids. Use of hexane/isopropanol
solvent systems led to a maximum of 75% recovery. The best lipid yield was achieved by a two-step extraction with ethanol
and hexane (120%). Extraction efficiency of the other solvent systems reached a maximum of 73%. Triacylglycerols were the
main structures of lipid isolated; only methanol-extracted lipid contained 58.5% phospholipids. The fatty acid content of
total recovered lipid was variable and depended on both the lipid class composition and the solvent system. GLA concentrations
in total lipids isolated by hexane/alcohol procedures (7.3–10.7%) are comparable with classical chloroform/methanol systems
(6.5–10.0%). The maximal GLA yield was obtained with chloroform/methanol/n-butanol/water/0.1 M ethylenediaminetetraacetic acid (EDTA) (2∶1∶1∶1∶0.1, by vol) and after two-step extraction with ethanol
and hexane (14.3 and 13.7 g GLA/kg DCW, respectively). The highest GLA content was analyzed in the phospholipid fraction (16.1%)
after using chloroform/methanol/n-butanol/water/0.1 M EDTA (2∶1∶1∶1∶0.1, by vol). Remarkably low concentrations of polyunsaturated fatty acids were determined
in the free fatty acid fraction.
Bread is a most important food product and source of selenium in Ukraine. However, low content of selenium in wheat flour from north and northwest regions of Ukraine does not ensure the recommended consumption of selenium. Daily intake of selenium by the population of North Ukraine is below recommended allowance. The aim of this research was to study the production of the dietary rolls with selenium-enriched yeast for the population of North Ukraine. The study showed that to obtain bakery yeast of good quality, concentration of sodium hydroselenite in the medium for yeast cultivation should be in the range from 2 to 5 μg Se/ml. Under these concentrations of selenium in medium, specific growth rate and biomass yield as well as bakery properties of the yeast Saccharomyces cerevisiae did not differ from the parameters of yeast, grown in the medium without selenium. Maturation of the selenium-enriched yeast improved their bakery properties. The 100 g wheat roll prepared with selenium-enriched yeast contained 50 μg Se (25% of the recommended daily allowance) in the form of selenomethionine, which is the best form of selenium for human consumption. These rolls can be used as a dietary product to reach recommended daily consumption of selenium by the population of North Ukraine and Chernobyl region.
Natural fermentative medium for selenium-enriched yeast (Saccharomyces cerevisiae) culture was investigated using response surface methodology (RSM). The medium with a concentration of 15 μg/mL Na2SeO3, contained various ratios of juices from germinated brown rice (0.40 ∼ 0.80, 12 Brix), beerwort (0.10 ∼ 0.50, 12 Brix) and soybean sprout (0.10 ∼ 0.50, 12 Brix), which were optimized by applying d-optimal mixture design (DMD). The effects of their ratios on biomass yield and total selenium (Se) yield were analyzed. The results showed that when the mixed ratio of the components was 4:4:2 (v:v:v), the maximum value of biomass yield and total Se yield were 8.5 g/L and 3.53 mg/L, respectively. Verification experimental trials were performed for validating the models, and it indicated that the above mixture of these natural materials can be used as proper medium for the growth of selenium-enriched yeast and accumulation of Se.
Increasing demand for biologically important polyunsaturated fatty acids has led to the search for alternative sources, especially fungi. Although successes in this area have induced interest in developing fungal fermentation processes, manipulation of their lipid composition requires new biotechnological strategies to achieve high yields of the desired polyunsaturated fatty acids. Fungal desaturase mutants with unique enzyme systems are useful not only for the regulation and overproduction of valuable polyunsaturated fatty acids but also because they are excellent models for the elucidation of fungal lipogenesis.
Effect of cadmium on the growth and lipid composition in three Aureobasidium pullulans strains grown in the presence and absence of extracellular polysaccharides was studied. Strains tolerated up to 1 mM Cd2+ in medium, but addition of either pectin or pullulan to medium increased tolerance to up to 2 mM Cd2+. While cadmium enhanced lipid accumulation notably only in strains of CCY 27-1-98 and CCY 27-1-111, strain CCY 27-1-115 displayed considerably high levels of sterols. Cadmium increased fatty acid unsaturation rapidly in phosphatidylethanolamine in all strains, owing to elevated levels of linoleic acid in this lipid fraction. On the other hand, Cd2+ ions significantly lowered conversion of oleic acid to linoleic acid in phosphatidylcholine only in the strain CCY 27-1-115. Nevertheless, addition of either pullulan or pectin amplified the ratio of C18:C16 fatty acids and the degree of fatty acid unsaturation in all membrane lipids as a result of induced biotransformation of stearate to oleate and linoleate. It was concluded that more saturated membranes with preferred C18 fatty acyl chains and high sterol amounts in the strain CCY 27-1-115 might be connected with its lower capacity to form pullulan as a protective metabolite against heavy metals compared with the other two strains.
Selenium levels in soil generally reflect its presence in food and the Se levels in human populations. Se food content is influenced by geographical location, seasonal changes, protein content and food processing. Periodic monitoring of Se levels in soil and food is necessary. Diet is the major Se source and approximately 80% of dietary Se is absorbed depending on the type of food consumed. Se bioavailability varies according to the Se source and nutritional status of the subject, being significantly higher for organic forms of Se. Se supplements can be beneficial for subjects living in regions with very low environmental levels of Se. Several strategies have been followed: (1) employment of Se-enriched fertilizers; (2) supplementation of farm animals with Se; (3) consumption of multimicronutrient supplements with Se. Nevertheless, detailed investigations of possible interactions between Se supplements and other food components and their influence on Se bioavailability are needed. Suppliers also need to provide more information on the specific type of Se used in supplements. In addition, research is lacking on the mechanisms through which Se is involved in hepatocyte damage during hepatopathies. Although Se potential as an antioxidant for the prevention of cardiovascular diseases (CVD) is promising, additional long-term intervention trials are necessary. As a result, indiscriminate Se supplements cannot be reliably recommended for the prevention of CVD in human beings. Some interesting findings reported an association of Se intake with a reduced prevalence and risk for prostate and colon cancer. However, random trials for other cancer types are inconclusive. As a final conclusion, the general population should be warned against the employment of Se supplements for prevention of hepatopathies, cardiovascular or cancer diseases, because benefits of Se supplementation are still uncertain, and their indiscriminate use could generate an increased risk of Se toxicity.
The biosynthesis of C18 polyunsaturated fatty acids has been studied in the fungus Mucor circinelloides. Microsomal membrane preparations contained delta9, delta12 and delta6 desaturase activities. The delta9 desaturase exhibited characteristics similar to those of the animal and yeast delta9 desaturases in being membrane bound and utilising stearoyl-CoA as substrate. Cytochrome b5 (a soluble form lacking the 20-amino-acid hydrophobic C-terminus) stimulated desaturation and was identified as a major cytochrome component of the membranes. A high ferricyanide reductase activity (indicative of NADH:cytochrome b5 reductase activity) coupled to inhibition by cyanide further supported the similarity with the mammalian and yeast enzymes. Time-course studies with radiolabelled oleoyl-CoA showed that the oleate [18:1(9)] was transferred to position sn-2 of phosphatidylcholine (PtdCho) and was desaturated to linoleoyl-PtdCho. Removal of the excess oleoyl-CoA from the membranes prior to addition of reductant confirmed that oleoyl-PtdCho is a substrate for the delta12 desaturase. The entry of oleate at this position of the phospholipid was facilitated by the activity of lyso-PtdCho:acyl-CoA acyltransferase (LPCAT), which readily transferred oleate from oleoyl-CoA to lyso-PtdCho. Desaturation of oleate at the sn-1 position of PtdCho was also demonstrated after the entry of oleate in to the phospholipid by the enzymes of the Kennedy pathway. Thus oleate at sn-1 and sn-2 positions served as substrate for the delta12 desaturase and is consistent with observations in oil seed tissues. LPCAT activity was substantially higher than that observed with lysophosphatidylethanolamine:acyl-CoA acyltransferase (LPEAT) indicating that oleate is less effectively channelled to phosphatidylethanolamine for linoleate synthesis. No desaturation on phosphatidylinositol could be demonstrated. Delta6 desaturase utilised linoleate at the sn-2 position of exogenously supplied PtdCho presented to the membranes in the presence of reductant. Thus, the entry of substrates into PtdCho via LPCAT and the synthesis of linoleate [18:2(9,12)] and gamma-linolenate [18:3(6,9,12)] on this phospholipid is similar to that reported for oil seed membranes.
Electroporation was used as a method for Rhodotorula rubra biomass enrichment in selenium. The highest selenium accumulation in yeast cells was achieved after 10 min pulse electric field (PEF) exposure of 16 h shaken culture. Multiple PEF exposure of yeast culture did not favour selenium accumulation. Optimization of selenium concentration in a medium resulted in an over two-fold increase of its accumulation in cells. About three-fold increase of dead yeast cells was recorded in analysed range of selenium concentrations.
Selenium is an essential element for human health. It has been recognized as an antioxidant and chemopreventive agent in cancer. Selenium is known to develop its biological activity via selenocysteine residue in the catalytically active centre of selenoproteins. The main source of selenium in human beings is the diet. However, in several regions of the world the content of selenium in diet has been estimated insufficient for a correct expression of the proteins. The beneficial effects of selenium on human health are strongly dependent on its chemical form and concentration. This review critically evaluated the state-of-the art of selenium speciation in biological matrices mainly focused in nutritional and food products. Besides the number of publications related to selenium speciation, isolation and accurate characterization and quantification of selenium species is still a challenge. Hyphenated techniques based on coupling chromatography separation with inductively coupled plasma spectrometry (ICP-MS) and its combination with molecular mass spectrometry (ESI-MS, ESI-MS-MS and MALDI-TOF) and isotopic dilution allow identification, quantification and structural characterization of selenium species. Particular attention is paid in the development of Se-enriched food and nutritional products and how the application of the techniques mentioned above is mandatory to get reliable results on selenium metabolisms in these particular matrices.
Background: Nutritional research has focused on the effects of specific nutrients' ability to cause or prevent cancer. While beta-carotene and selenium (both important for antioxidant systems) have cancer prevention capabilities, their antineoplastic mechanism(s) remains to be elucidated. Methods: In a prospective, randomized study design we evaluated immunological changes in free-living, healthy aged humans (57-84 years of age) given a placebo, beta-carotene (45 mg/day), and/or selenium (400 µg/day) supplement for 6 months and after 2 months of discontinuation. Peripheral blood lymphocytes were evaluated and subtyped using flowcytometry. Natural killer (NK) cell cytotoxicity was determined by a fluorescent method. Plasma diene conjugates were assessed to evaluate changes in oxidative stress. Results: Selenium and selenium plus beta-carotene supplementation caused an increase in total T cells by 27% and 31%, respectively (p <.05). The only group that was different (in T lymphocytes) from the controls (placebo group) after 6 months of supplementation (p <.05) was the selenium-supplemented group (+65%). Much of this increase was the result of an increase in CD4(+) T-cell subsets. Selenium or beta-carotene supplementation for 3 months increased NK cell cytotoxicity over pretreatment levels by 58% and 34%, respectively; however, these levels returned to +12% and -6% of pretreatment levels after 6 months supplementation. Selenium plus beta-carotene supplementation caused an increase in the percentage of NK cell by 121% and 161% at 3 and 6 months, respectively. However, the increased numbers of NK cells were not correlated with NK cell activity. Conclusions: We found that selenium enhanced immune function (NK cell cytotoxicity) and phenotypic expression of T-cell subsets, whereas beta-carotene affected only immune function. Increased NK cell cytotoxicity may last for only a short period of supplementation and was not sustained throughout the 6 months of supplementation. Supplemental selenium and beta-carotene seemed to affect immune function in aged subjects by different mechanisms.
Selenium (Se) is an essential trace element for animals and humans that is obtained from dietary sources including cereals, grains and vegetables. The Se content of plants varies considerably according to its concentration in soil. Plants convert Se mainly into Se-methionine (Se-Met) and incorporate it into protein in place of methionine (Met). Selenocystine (Se-Cys), methyl-Se-Cys and gamma-glutamyl-Se-methyl-Cys are not significantly incorporated into plant protein and are at relatively low levels irrespective of soil Se content. Higher animals are unable to synthesize Se-Met and only Se-Cys was detected in rats supplemented with Se as selenite. Renal regulation is the mode by which whole body Se is controlled. Se is concentrated in hair and nail and it occurs almost exclusively in organic compounds. The potentiating effect of Se deficiency on lipid peroxidation is enhanced in some tissues by concurrent deficiency of copper or manganese. In the in vitro system, the chemical form of Se is an important factor in eliciting cellular responses. Although the cytotoxic mechanisms of selenite and other redoxing Se compounds are still unclear, it has been suggested that they derive from their ability to catalyze the oxidation of thiols and to produce superoxide simultaneously. Selenite-induced cytotoxicity and apoptosis in human carcinoma cells can be inhibited with copper (CuSO(4)) as an antioxidant. High doses of selenite result in induction of 8-hydroxydeoxyguanosine (8-OHdG) in mouse skin cell DNA and in primary human keratinocytes. It may cause DNA fragmentation and decreased DNA synthesis, cell growth inhibition, DNA synthesis, blockade of the cell cycle at the S/G(2)-M phase and cell death by necrosis. In contrast, in cells treated with methylselenocyanate or Se methylselenocysteine, the cell cycle progression was blocked at the G(1) phase and cell death was predominantly induced by apoptosis.
The hepatic fatty acid metabolism was investigated in rats stressed by selenium deficiency and enhanced fish oil intake. Changes in the composition of lipids, peroxides, and fatty acids were studied in the liver of rats fed either a Sedeficient (8 microg Se/kg) or a Se-adequate (300 microg Se/kg) diet, both rich in n-3 fatty acid-containing fish oil (100 g/kg diet) and vitamin E (146 mg alpha-tocopherol/kg diet). The two diets were identical except for their Se content. Se deficiency led to a decrease in hair coat density and quality as well as to changes in liver lipids, individual lipid fractions and phospholipid fatty acid composition of the liver. The low Se status did reduce total and reduced glutathione in the liver but did not affect the hepatic malondialdehyde level. In liver phospholipids (PL), Se deficiency significantly reduced levels of palmitic acid [16:0], fatty acids of the n-3 series such as DHA [22:6 n-3], and other long-chain polyunsaturates C-20-C-22, but increased n-6 fatty acids such as linoleic acid (LA) [18:2 n-6]. Thus, the conversion of LA to arachidonic acid was reduced and the ratio of n-6/n-3 fatty acids was increased. As in liver PL, an increase in the n-6/n-3 ratio was also observed in the mucosal total fatty acids of the small intestine. These results suggest that in rats with adequate vitamin E and enhanced fish oil intake, Se deficiency affects the lipid concentration and fatty acid composition in the liver. The changes may be related to the decreased levels of selenoenzymes with antioxidative functions. Possible effects of Se on absorption, storage and desaturation of fatty acids were also discussed.
Semi-metals (boron, silicon, arsenic and selenium) form organo-metal compounds, some of which are found in nature and affect the physiology of living organisms. They include, e.g., the boron-containing antibiotics aplasmomycin, borophycin, boromycin, and tartrolon or the silicon compounds present in "silicate" bacteria, relatives of the genus Bacillus, which release silicon from aluminosilicates through the secretion of organic acids. Arsenic is incorporated into arsenosugars and arsenobetaines by marine algae and invertebrates, and fungi and bacteria can produce volatile methylated arsenic compounds. Some prokaryotes can use arsenate as a terminal electron acceptor while others can utilize arsenite as an electron donor to generate energy. Selenium is incorporated into selenocysteine that is found in some proteins. Biomethylation of selenide produces methylselenide and dimethylselenide. Selenium analogues of amino acids, antitumor, antibacterial, antifungal, antiviral, anti-infective drugs are often used as analogues of important pharmacological sulfur compounds. Other metalloids, i.e. the rare and toxic tellurium and the radioactive short-lived astatine, have no biological significance.
Selenium bio-accumulation in Saccharomyces cerevisiae cells
- A Danch
- J Chmielowski