Insight into selenium biofortification and the selenite metabolic mechanism of Monascus ruber M7.

Monascus species are functional fermentation fungi with great potential for selenium (Se) supplementation. This study investigated the effects of Se bio-fortification on the growth, morphology, and biosynthesis of Monascus ruber M7. The results demonstrated a significant increase in the yield of orange and red Monascus pigments (MPs) in red yeast rice (RYR) by 38.52% and 36.57%, respectively, under 20 µg/mL of selenite pressure. Meanwhile, the production of citrinin (CIT), a mycotoxin, decreased from 244.47 µg/g to 175.01 µg/g. Transcriptome analysis revealed significant upregulation of twelve genes involved in MPs biosynthesis, specifically MpigE, MpigF, and MpigN, and downregulation of four genes (mrr3, mrr4, mrr7, and mrr8) associated with CIT biosynthesis. Additionally, three genes encoding cysteine synthase cysK (Log2FC = 1.6), methionine synthase metH (Log2FC = 2.2), and methionyl-tRNA synthetase metG (Log2FC = 1.8) in selenocompound metabolism showed significantly upregulated. These findings provide insights into Se biotransformation and metabolism in filamentous fungi.

Disruption of the cell division protein ftsK gene changes elemental selenium generation, selenite tolerance, and cell morphology in Rahnella aquatilis HX2.

AIMS: Some studies have indicated that the alterations in cellular morphology induced by selenite [Se(Ⅳ)] may be attributed to its inhibitory effects on cell division. However, whether the genes associated with cell division are implicated in Se(Ⅳ) metabolism remains unclear. METHODS AND RESULTS: The ftsK gene in Rahnella aquatilis HX2 was mutated with an in-frame deletion strategy. The ftsK mutation strongly reduced the tolerance to selenite [Se(Ⅳ)] and the production of red elemental selenium [Se(0)] in R. aquatilis HX2, and this effect could not be attributed solely to the inhibition of cell growth. Deleting the ftsK gene also resulted in a significant decrease in bacterial growth of R. aquatilis HX2 during both exponential and stationary phases. The deletion of ftsK inhibited cell division, resulting in the development of elongated filamentous cells. Furthermore, the loss-of-function of FtsK significantly impacted the expression of seven genes linked to cell division and Se(Ⅳ) metabolism by at least 2-fold, as unveiled by real-time quantitative PCR (RT-qPCR) under Se(Ⅳ) treatment. CONCLUSIONS: These findings suggest that FtsK is associated with Se(Ⅳ) tolerance and Se(0) generation and is a key player in coordinating bacterial growth and cell morphology in R. aquatilis HX2.

Electroactive Brevundimonas diminuta consortium mediated selenite bioreduction, biogenesis of selenium nanoparticles and bio-electricity generation.

In this study, highly selenite-resistant strains belonging to Brevundimonas diminuta (OK287021, OK287022) genus were isolated from previously operated single chamber microbial fuel cell (SCMFC). The central composite design showed that the B. diminuta consortium could reduce selenite. Under optimum conditions, 15.38 Log CFU mL-1 microbial growth, 99.08% Se(IV) reduction, and 89.94% chemical oxygen demand (COD) removal were observed. Moreover, the UV-visible spectroscopy (UV) and Fourier transform infrared spectroscopy (FTIR) analyses confirmed the synthesis of elemental selenium nanoparticles (SeNPs). In addition, transmission electron microscopy (TEM) and scanning electron microscope (SEM) revealed the formation of SeNPs nano-spheres. Besides, the bioelectrochemical performance of B. diminuta in the SCMFC illustrated that the maximum power density was higher in the case of selenite SCMFCs than those of the sterile control SCMFCs. Additionally, the bioelectrochemical impedance spectroscopy and cyclic voltammetry characterization illustrated the production of definite extracellular redox mediators that might be involved in the electron transfer progression during the reduction of selenite. In conclusion, B. diminuta whose electrochemical activity has never previously been reported could be a suitable and robust biocatalyst for selenite bioreduction along with wastewater treatment, bioelectricity generation, and economical synthesis of SeNPs in MFCs.

Reduction of selenite to selenium nanoparticles by highly selenite-tolerant bacteria isolated from seleniferous soil.

The microbial reduction of selenite to elemental selenium nanoparticles (SeNPs) is thought to be an effective detoxification process of selenite for many bacteria. In this study, Metasolibacillus sp. ES129 and Oceanobacillus sp. ES111 with high selenite reduction efficiency or tolerance were selected for systematic and comparative studies on their performance in selenite removal and valuable SeNPs recovery. The kinetic monitoring of selenite reduction showed that the highest transformation efficiency of selenite to SeNPs was achieved at a concentration of 4.24 mM for ES129 and 4.88 mM for ES111. Ultramicroscopic analysis suggested that the SeNPs produced by ES111 and ES129 had been formed in cytoplasm and subsequently released to extracellular space through cell lysis process. Furthermore, the transcriptome analysis indicated that the expression of genes involved in bacillithiol biosynthesis, selenocompound metabolism and proline metabolism were significantly up-regulated during selenite reduction, suggesting that the transformation of selenite to Se0 may involve multiple pathways. Besides, the up-regulation of genes associated with nucleotide excision repair and antioxidation-related enzymes may enhance the tolerance of bacteria to selenite. Generally, the exploration of selenite reduction and tolerance mechanisms of the highly selenite-tolerant bacteria is of great significance for the effective utilization of microorganisms for environmental remediation.

Modulation of oxidative stress machinery determines the contrasting ability of cyanobacteria to adapt to Se(VI) or Se(IV).

Excess of selenium (Se) in aquatic ecosystems has necessitated thorough investigations into the effects/consequences of this metalloid on the autochthonous organisms exposed to it. The molecular details of Se-mediated adaptive response remain unknown in cyanobacteria. This study aims to uncover the molecular mechanisms driving the divergent physiological responses of cyanobacteria on exposure to selenate [Se(VI)] or selenite [Se(IV)], the two major water-soluble oxyanions of Se. The cyanobacterium, Anabaena PCC 7120, withstood 0.4 mM of Se(VI), whereas even 0.1 mM of Se(IV) was detrimental, affecting photosynthesis and enhancing endogenous ROS. Surprisingly, Anabaena pre-treated with Se(VI), but not Se(IV), showed increased tolerance to oxidative stress mediated by H2O2/methyl viologen. RNA-Seq analysis showed Se(VI) to elevate transcription of genes encoding anti-oxidant proteins and Fe-S cluster biogenesis, whereas the photosynthesis-associated genes, which were mainly downregulated by Se(IV), remained unaffected. Specifically, the content of typical 2-Cys-Prx (Alr4641), a redox-maintaining protein in Anabaena, was elevated with Se(VI). In comparison to the wild-type, the Anabaena strain over-expressing the Alr4641 protein (An4641+) showed enhanced tolerance to Se(VI) stress, whereas the corresponding knockdown-strain (KD4641) was sensitive to this stressor. Incidentally, among these strains, only An4641+ was better protected from the ROS-mediated damage caused by high dose of Se(VI). These results suggest that altering the content of the antioxidant protein 2-Cys-Prx, could be a potential strategy for modulating resistance to selenate. Thus, involvement of oxidative stress machinery appears to be the major determinant, responsible for the contrasting physiological differences observed in response to selenate/selenite in cyanobacteria.

Achromobacter seleniivolatilans sp. nov. and Buttiauxella selenatireducens sp. nov., isolated from the rhizosphere of selenium hyperaccumulator Cardamine hupingshanesis.

Two Gram-stain-negative bacterial strains, R39T and R73T, were isolated from the rhizosphere soil of the selenium hyperaccumulator Cardamine hupingshanesis in China. Strain R39T transformed selenite into elemental and volatile selenium, whereas strain R73T transformed both selenate and selenite into elemental selenium. Phylogenetic and phylogenomic analyses indicated that strain R39T belonged to the genus Achromobacter, while strain R73T belonged to the genus Buttiauxella. Strain R39T (genome size, 6.68 Mb; G+C content, 61.6 mol%) showed the closest relationship to Achromobacter marplatensis LMG 26219T and Achromobacter kerstersii LMG 3441T, with average nucleotide identity (ANI) values of 83.6 and 83.4 %, respectively. Strain R73T (genome size, 5.22 Mb; G+C content, 50.3 mol%) was most closely related to Buttiauxella ferragutiae ATCC 51602T with an ANI value of 86.4 %. Furthermore, strain A111 from the GenBank database was found to cluster with strain R73T within the genus Buttiauxella through phylogenomic analyses. The ANI and digital DNA-DNA hybridization values between strains R73T and A111 were 97.5 and 80.0% respectively, indicating that they belong to the same species. Phenotypic characteristics also differentiated strain R39T and strain R73T from their closely related species. Based on the polyphasic analyses, strain R39T and strain R73T represent novel species of the genera Achromobacter and Buttiauxella, respectively, for which the names Achromobacter seleniivolatilans sp. nov. (type strain R39T=GDMCC 1.3843T=JCM 36009T) and Buttiauxella selenatireducens sp. nov. (type strain R73T=GDMCC 1.3636T=JCM 35850T) are proposed.

Multi-pathways-mediated mechanisms of selenite reduction and elemental selenium nanoparticles biogenesis in the yeast-like fungus Aureobasidium melanogenum I15.

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.

Selenite selectively kills lung fibroblasts to treat bleomycin-induced pulmonary fibrosis.

BACKGROUND: Interstitial lung disease (ILD) treatment is a critical unmet need. Selenium is an essential trace element for human life and an antioxidant that activates glutathione, but the gap between its necessity and its toxicity is small and requires special attention. Whether selenium can be used in the treatment of ILD remains unclear. METHODS: We investigated the prophylactic and therapeutic effects of selenite, a selenium derivative, in ILD using a murine model of bleomycin-induced idiopathic pulmonary fibrosis (IPF). We further elucidated the underlying mechanism using in vitro cell models and examined their relevance in human tissue specimens. The therapeutic effect of selenite in bleomycin-administered mice was assessed by respiratory function and histochemical changes. Selenite-induced apoptosis and reactive oxygen species (ROS) production in murine lung fibroblasts were measured. RESULTS: Selenite, administered 1 day (inflammation phase) or 8 days (fibrotic phase) after bleomycin, prevented and treated deterioration of lung function and pulmonary fibrosis in mice. Mechanistically, selenite inhibited the proliferation and induced apoptosis of murine lung fibroblasts after bleomycin treatment both in vitro and in vivo. In addition, selenite upregulated glutathione reductase (GR) and thioredoxin reductase (TrxR) in murine lung fibroblasts, but not in lung epithelial cells, upon bleomycin treatment. GR and TrxR inhibition eliminates the therapeutic effects of selenite. Furthermore, we found that GR and TrxR were upregulated in the human lung fibroblasts of IPF patient samples. CONCLUSIONS: Selenite induces ROS production and apoptosis in murine lung fibroblasts through GR and TrxR upregulation, thereby providing a therapeutic effect in bleomycin-induced IPF.

Continuous selenite biotransformation and biofuel production by marine diatom in the presence of fulvic acid.

In this study, the biochemical response of Phaeodactylum tricornutum to varying concentrations of inorganic selenium (Se) was investigated. It was observed that, when combined with fulvic acid, P. tricornutum exhibited enhanced uptake and biotransformation of inorganic Se, as well as increased microalgal lipid biosynthesis. Notably, when subjected to moderate (5 and 10 mg/L) and high (20 and 40 mg/L) concentrations of selenite under fulvic acid treatment, there was a discernible redirection of carbon flux towards lipogenesis and protein biosynthesis from carbohydrates. In addition, the key parameters of microalgae-based biofuels aligned with the necessary criteria outlined in biofuel regulations. Furthermore, the Se removal capabilities of P. tricornutum, assisted by fulvic acid, were coupled with the accumulation of substantial amounts of organic Se, specifically SeCys. These findings present a viable and successful approach to establish a microalgae-based system for Se uptake and biotransformation.

In vitro study on the competitive reactions between arsenite and selenite with glutathione.

Exposure to arsenic can cause various biological effects by increasing the production of reactive oxygen species (ROS). Selenium acts as a beneficial element by regulating ROS and limiting heavy metal uptake and translocation. There are studies on the interactive effects of As and Se in plants, but the antagonistic and synergistic effects of these elements based on their binding to glutathione (GSH) molecules have not been studied yet. In this study, we aimed to investigate the antagonistic or synergistic effects of As and Se on the binding mechanism of Se and As with GSH at pH 3.0, 5.0, or 6.5. The interaction of As and Se in Se(SG)2 + As(III) or As(SG)3 + Se(IV) binary systems and As(III) + Se(IV) + GSH ternary system were examined depending on their ratios via liquid chromatography diode array detector/electrospray mass spectrometry (LC-DAD/MS) and liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS). The results showed that the formation of As(GS)3 was not detected in the As(III) + Se(SG)2 binary system, indicating that As(III) did not affect the stability of Se(SG)2 complex antagonistically. However, in the Se(IV) + As(SG)3 binary system, the addition of Se(IV) to As(SG)3 affected the stability of As(SG)3 antagonistically. Se(IV) reacted with GSH, disrupting the As(SG)3 complex, and consequently, Se(SG)2 formation was measured using LC-MS/DAD. In the Se(IV) + GSH + As(III) ternary system, Se(SG)2 formation was detected upon mixing As(III), Se(IV), and GSH. The increase in the concentration of As(III) did not influence the stability of the Se(SG)2 complex. Additionally, Se(IV) has a higher affinity than As(III) to the GSH, regardless of the pH of the solution. In both binary and ternary systems, the formation of the by-product glutathione trisulfide (GSSSG) was detected using LC-ESI-MS/MS.

Biochemical and molecular responses of the ascorbate-glutathione cycle in wheat seedlings exposed to different forms of selenium.

Biofortification aims to increase selenium (Se) concentration and bioavailability in edible parts of crops such as wheat (Triticum aestivum L.), resulting in increased concentration of Se in plants and/or soil. Higher Se concentrations can disturb protein structure and consequently influence glutathione (GSH) metabolism in plants which can affect antioxidative and other detoxification pathways. The aim of this study was to elucidate the impact of five different concentrations of selenate and selenite (0.4, 4, 20, 40 and 400 mg kg-1) on the ascorbate-glutathione cycle in wheat shoots and roots and to determine biochemical and molecular tissue-specific responses. Content of investigated metabolites, activities of detoxification enzymes and expression of their genes depended both on the chemical form and concentration of the applied Se, as well as on the type of plant tissue. The most pronounced changes in the expression level of genes involved in GSH metabolism were visible in wheat shoots at the highest concentrations of both forms of Se. Obtained results can serve as a basis for further research on Se toxicity and detoxification mechanisms in wheat. New insights into the Se impact on GSH metabolism could contribute to the further development of biofortification strategies.

Assessment of dietary Selenium and its role in Mercury fate in cultured fish rainbow trout with two sustainable aquafeeds.

This study enhances the current limited understanding of the interaction between mercury (Hg) and selenium (Se) species in fish. Rainbow trout (Oncorhynchus mykiss), a model aquaculture fish, was exposed to Hg and Se species through controlled dietary conditions. Over a 6-month feeding trial, the impact of dietary Se on Hg bioaccumulation in fish, including flesh, brain, and liver, was tracked. Twelve dietary conditions were tested, including plant-based diets (0.25 µgSe g-1) and tuna byproduct diets (0.25 µgHg g-1, 8.0 µgSe g-1) enriched with methylmercury and/or Se as selenite or selenomethionine. The tuna byproduct diet resulted in lower Hg levels than the plant-based diets, with muscle Hg content below the European Commission's safe threshold. This study highlights the significant impact of specific Se compounds in the diet, particularly from tuna-based aquafeed, on Hg bioaccumulation. These promising results provide a strong recommendation for future use of fisheries byproducts in sustainable aquafeeds.

The actinomycete Kitasatospora sp. SeTe27, subjected to adaptive laboratory evolution (ALE) in the presence of selenite, varies its cellular morphology, redox stability, and tolerance to the toxic oxyanion.

The effects of oxyanions selenite (SeO32-) in soils are of high concern in ecotoxicology and microbiology as they can react with mineral particles and microorganisms. This study investigated the evolution of the actinomycete Kitasatospora sp. SeTe27 in response to selenite. To this aim, we used the Adaptive Laboratory Evolution (ALE) technique, an experimental approach that mimics natural evolution and enhances microbial fitness for specific growth conditions. The original strain (wild type; WT) isolated from uncontaminated soil gave us a unique model system as it has never encountered the oxidative damage generated by the prooxidant nature of selenite. The WT strain exhibited a good basal level of selenite tolerance, although its growth and oxyanion removal capacity were limited compared to other environmental isolates. Based on these premises, the WT and the ALE strains, the latter isolated at the end of the laboratory evolution procedure, were compared. While both bacterial strains had similar fatty acid profiles, only WT cells exhibited hyphae aggregation and extensively produced membrane-like vesicles when grown in the presence of selenite (challenged conditions). Conversely, ALE selenite-grown cells showed morphological adaptation responses similar to the WT strain under unchallenged conditions, demonstrating the ALE strain improved resilience against selenite toxicity. Whole-genome sequencing revealed specific missense mutations in genes associated with anion transport and primary and secondary metabolisms in the ALE variant. These results were interpreted to show that some energy-demanding processes are attenuated in the ALE strain, prioritizing selenite bioprocessing to guarantee cell survival in the presence of selenite. The present study indicates some crucial points for adapting Kitasatospora sp. SeTe27 to selenite oxidative stress to best deal with selenium pollution. Moreover, the importance of exploring non-conventional bacterial genera, like Kitasatospora, for biotechnological applications is emphasized.

Arsenite Mediates Selenite Resistance and Reduction in Enterobacter sp. Z1, Thereby Enhancing Bacterial Survival in Selenium Environments.

Arsenic (As) is widely present in the environment, and virtually all bacteria possess a conserved ars operon to resist As toxicity. High selenium (Se) concentrations tend to be cytotoxic. Se has an uneven regional distribution and is added to mitigate As contamination in Se-deficient areas. However, the bacterial response to exogenous Se remains poorly understood. Herein, we found that As(III) presence was crucial for Enterobacter sp. Z1 to develop resistance against Se(IV). Se(IV) reduction served as a detoxification mechanism in bacteria, and our results demonstrated an increase in the production of Se nanoparticles (SeNPs) in the presence of As(III). Tandem mass tag proteomics analysis revealed that the induction of As(III) activated the inositol phosphate, butanoyl-CoA/dodecanoyl-CoA, TCA cycle, and tyrosine metabolism pathways, thereby enhancing bacterial metabolism to resist Se(IV). Additionally, arsHRBC, sdr-mdr, purHD, and grxA were activated to participate in the reduction of Se(IV) into SeNPs. Our findings provide innovative perspectives for exploring As-induced Se biotransformation in prokaryotes.

Effects of selenium nanoparticles produced by Lactobacillus acidophilus HN23 on lipid deposition in WRL68 cells.

Selenium is an essential trace element for most organisms, protecting cells from oxidative damage caused by free radicals and serving as an adjunctive treatment for non-alcoholic fatty liver disease (NAFLD). In this study, We used the lactic acid bacterium Lactobacillus acidophilus HN23 to reduce tetra-valent sodium selenite into particulate matter, and analyzed it through inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), X-ray diffraction energy dispersive spectrometry (EDS), and Fourier transform infrared spectroscopy (FTIR). We found that it consisted of selenium nanoparticles (SeNPs) with a mass composition of 65.8 % zero-valent selenium and some polysaccharide and polypeptide compounds, with particle sizes ranging from 60 to 300 nm. We also detected that SeNPs were much less toxic to cells than selenite. We further used free fatty acids (FFA)-induced WRL68 fatty liver cell model to study the therapeutic effect of SeNPs on NAFLD. The results show that SeNPs are more effective than selenite in reducing lipid deposition, increasing mitochondrial membrane potential (MMP) and antioxidant capacity of WRL68 cells, which is attributed to the chemical valence state of selenium and organic composition in SeNPs. In conclusion, SeNPs produced by probiotics L. acidophilus had the potential to alleviate NAFLD by reducing hepatocyte lipid deposition and oxidative damage. This study may open a new avenue for SeNPs drug development to treat NAFLD.

Molecular mechanisms of selenite reduction by Lactiplantibacillus plantarum BSe: An integrated genomic and transcriptomic analysis.

The reduction of selenite [Se(Ⅳ)] by microorganisms is a green and efficient detoxification strategy. We found that Se(Ⅳ) inhibited exopolysaccharide and protein secretion by Lactiplantibacillus plantarum BSe and compromised cell integrity. In this study, L. plantarum BSe reduced Se(Ⅳ) by increasing related enzyme activity and electron transfer. Genomic analysis demonstrated that L. plantarum BSe should be able to reduce Se(Ⅳ). Further transcriptome analysis showed that L. plantarum BSe enhanced its tolerance to Se(Ⅳ) by upregulating the expression of surface proteins and transporters, thus reducing the extracellular Se(Ⅳ) concentration through related enzymatic reactions and siderophore-mediated pathways. Lactiplantibacillus plantarum BSe was able to regulate the expression of related genes involved in quorum sensing and a two-component system and then select appropriate strategies for Se(Ⅳ) transformation in response to varying environmental Se(Ⅳ) concentrations. In addition, azo reductase was linked to the reduction of Se(Ⅳ) for the first time. The present study established a multipath model for the reduction of Se(Ⅳ) by L. plantarum, providing new insights into the biological reduction of Se(Ⅳ) and the biogeochemical cycle of selenium.

Reduction of selenite and tellurite by a highly metal-tolerant marine bacterium / Reducción de selenita y telurito por una bacteria marina altamente tolerante a los metales

Selenium (Se) and tellurium (Te) contaminations in soils and water bodies have been widely reported in recent years. Se(IV) and Te(IV) were regarded as their most dangerous forms. Microbial treatments of Se(IV)- and Te(IV)-containing wastes are promising approaches because of their environmentally friendly and sustainable advantages. However, the salt-tolerant microbial resources that can be used for selenium/tellurium pollution control are still limited since industrial wastewaters usually contain a large number of salts. In this study, a marine Shewanella sp. FDA-1 (FDA-1) was reported for efficient Se(IV) and Te(IV) reduction under saline conditions. Process and product analyses were performed to investigate the bioreduction processes of Se(IV) and Te(IV). The results showed that FDA-1 can effectively reduce Se(IV) and Te(IV) to Se0 and Te0 Se(IV)/Te(IV) to Se0/Te0 in 72 h, which were further confirmed by XRD and XPS analyses. In addition, enzymatic and RT‒qPCR assays showed that flavin-related proteins, reductases, dehydrogenases, etc., could be involved in the bioreduction of Se(IV)/Te(IV). Overall, our results demonstrate the ability of FDA-1 to reduce high concentrations of Se(IV)/or Te(IV) to Se0/or Te0 under saline conditions and thus provide efficient microbial candidate for controlling Se and Te pollution.(AU)

In vitro digestion and fecal fermentation of selenocompounds: impact on gut microbiota, antioxidant activity, and short-chain fatty acids.

Selenium bioavailability is critically influenced by gut microbiota, yet the interaction dynamics with selenocompounds remain unexplored. Our study found that L-Selenomethionine (SeMet) and Se-(Methyl)seleno-L-cysteine (MeSeCys) maintained stability during in vitro gastrointestinal digestion. In contrast, Selenite and L-Selenocystine (SeCys2) were degraded by approximately 13% and 35%. Intriguingly, gut microflora transformed MeSeCys, SeCys2, and Selenite into SeMet. Moreover, when SeCys2 and Selenite incubated with gut microbiota, they produced red selenium nanoparticles with diameters ranging between 100 and 400 nm and boosted glutathione peroxidase activity. These changes were positively associated with an increased relative abundance of unclassified_g__Blautia (Family Lachnospiraceae), Erysipelotrichaceae_UCG-003 (Family Erysipelatoclostridiaceae), and uncultured_bacterium_g__Subdoligranulum (Family Ruminococcaceae). Our findings implied that differential microbial sensitivities to selenocompounds, potentially attributable to their distinct mechanisms governing selenium uptake, storage, utilization, and excretion.

Nitrate reductase involves in selenite reduction in Rahnella aquatilis HX2 and the characterization and anticancer activity of the biogenic selenium nanoparticles.

BACKGROUND: Biogenic selenium nanoparticles (SeNPs) show numerous advantages including their high stability, low toxicity, and high bioactivity. While metabolism of SeNPs remains not well studied and need more investigation to reveal the process. PURPOSE: The objective of the study was to investigate the relationship between nitrate reductase and selenite reduction in Rahnella aquatilis HX2, characterize the properties of HX2 produced SeNPs, and explore their potential applications, particularly their anticancer activity. PROCEDURES: Selenium species were measured by high-performance liquid chromatography coupled to inductively coupled plasma - Mass spectrometry (HPLC-ICP-MS). Transcription level of nitrate reductase was determined by Real-time quantitative PCR. Morphology, particle size, crystal structure and surface chemistry of SeNPs were determined by electron microscopy, dynamic light scattering method, Raman scattering, X-ray photoelectron spectroscopy, respectively. Anti cancer cell activity was measured by CCK-8 assay. MAIN FINDINGS: SeNP production in R. aquatilis HX2 was correlated with the cell growth. The products of selenite reduction in HX2 detected by HPLC-ICP-MS included SeNPs, selenocysteine (SeCys), Se-Methylselenocysteine (MeSeCys), and 7 unknown compounds. Nitrate addition experiments suggested the involvement of nitrate reductase in selenite reduction in HX2. Both the cellular membrane and cytoplasm of HX2 exhibited selenite-reducing ability, indicating that membrane-associated nitrate reductase was not the sole selenite reductase in HX2. Characterization of the biogenic SeNPs revealed a spherical morphology and amorphous structure of them. Surface chemistry analysis implicated the binding of extracellular polymeric substances to the biogenic SeNPs, and the presence of Se0, Se2-, and electron-rich Se atoms on the surface of SeNPs. Finally, the IC50 values of the biogenic SeNPs were 36.49 µM for HepG2 and 3.70 µM for HeLa cells. CONCLUSIONS: The study first revealed that the nitrate reductase is involving in selenite reduction in R. aquatilis HX2. The biogenic SeNPs coordinated with organic substances in the surface. And SeNPs produced by R. aquatilis HX2 showed excellent anticancer activities on HepG2 and HeLa cells.

Co-metabolism of Na+/K+ ion regulated physiological enhancement on selenium-accumulation in Saccharomyces yeasts.

BACKGROUND: Selenium is an important nutritional supplement that mainly exists naturally in soil as inorganic selenium. Saccharomyces cerevisiae cells are excellent medium for converting inorganic selenium in nature into organic selenium. RESULTS: Under the co-stimulation of sodium selenite (Na2SeO3) and potassium selenite (K2SeO3), the activity of selenophosphate synthetase (SPS) was improved up to about five folds more than conventional Na2SeO3 group with the total selenite salts content of 30 mg/L. Transcriptome analysis first revealed that due to the sharing pathway between sodium ion (Na+) and potassium ion (K+), the K+ largely regulates the metabolisms of amino acid and glutathione under the accumulation of selenite salt. Furthermore, K+ could improve the tolerance performance and selenium-biotransformation yields of Saccharomyces cerevisiae cells under Na2SeO3 salt stimulation. CONCLUSION: The important role of K+ in regulating the intracellular selenium accumulation especially in terms of amino acid metabolism and glutathione, suggested a new direction for the development of selenium-enrichment supplements with Saccharomyces cerevisiae cell factory. © 2024 Society of Chemical Industry.