Bioconversion of inorganic selenium to less toxic selenium forms by microbes: A review

Accumulation and metabolism of selenium in the rare yeast Kazachstania unispora during the selenium enrichment process

Selenium (Se)-enriched yeast is a good nutritional source for human being. Kazachstania unispora (K. unispora) has shown the positive physiological functionality for human health, whose potential for Se enrichment, however, remains elusive. This study demonstrated the ability of K. unispora to convert inorganic Se to organic Se, and then comprehensively investigated the accumulation and metabolism of Se in K. unispora. The results indicated that K. unispora can effectively accumulate organic Se, of which 95% of absorbed Se was converted to organic forms. Among these organic Se, 46.17% of them was bound to protein and 16.78% was combined with polysaccharides. In addition, some of the organic Se was metabolized to selenomethionine (30.26%) and selenocystine (3.02%), during which four low-molecular weight selenometabolites were identified in K. unispora. These findings expand the scope of Se-enriched yeast species, and provide useful knowledge for further investigation of Se enrichment mechanism in K. unispora.

Unveiling Green Synthesis and Biomedical Theranostic paradigms of Selenium Nanoparticles (SeNPs) - A state-of-the-art comprehensive update

The advancements in nanotechnology, pharmaceutical sciences, and healthcare are propelling the field of theranostics, which combines therapy and diagnostics, to new heights; emphasizing the emergence of selenium nanoparticles (SeNPs) as versatile theranostic agents. This comprehensive update offers a holistic perspective on recent developments in the synthesis and theranostic applications of SeNPs, underscoring their growing importance in nanotechnology and healthcare. SeNPs have shown significant potential in multiple domains, including antioxidant, anti-inflammatory, anticancer, antimicrobial, antidiabetic, wound healing, and cytoprotective therapies. The review highlights the adaptability and biocompatibility of SeNPs, which are crucial for advanced disease detection, monitoring, and personalized treatment. Special emphasis is placed on advancements in green synthesis techniques, underscoring their eco-friendly and cost-effective benefits in biosensing, diagnostics, imaging and therapeutic applications. Additionally, the appraisal scrutinizes the progressive trends in smart stimuli-responsive SeNPs, conferring their role in innovative solutions for disease management and diagnostics. Despite their promising therapeutic and prophylactic potential, SeNPs also present several challenges, particularly regarding toxicity concerns. These challenges and their implications for clinical translation are thoroughly explored, providing a balanced view of the current state and prospects of SeNPs in theranostic applications.

Polysaccharides in fruits: Biological activities, structures, and structure-activity relationships and influencing factors-A review

Fruits are a rich source of polysaccharides, and an increasing number of studies have shown that polysaccharides from fruits have a wide range of biological functions. Here, we thoroughly review recent advances in the study of the bioactivities, structures, and structure-activity relationships of fruit polysaccharides, especially highlighting the structure-activity influencing factors such as extraction methods and chemical modifications. Different extraction methods cause differences in the primary structures of polysaccharides, which in turn lead to different polysaccharide biological activities. Differences in the degree of modification, molecular weight, substitution position, and chain conformation caused by chemical modification can all affect the biological activities of fruit polysaccharides. Furthermore, we summarize the applications of fruit polysaccharides in the fields of pharmacy and medicine, foods, cosmetics, and materials. The challenges and perspectives for fruit polysaccharide research are also discussed.

Unveiling the innovative green synthesis mechanism of selenium nanoparticles by exploiting intracellular protein elongation factor Tu from Bacillus paramycoides

Selenium nanoparticles (SeNPs) have garnered extensive research interest and shown promising applications across diverse fields owing to their distinctive properties, including antioxidant, anticancer, and antibacterial activity (Ojeda et al., 2020; Qu et al., 2023; Zambonino et al., 2021, 2023). Among the various approaches employed for SeNP synthesis, green synthesis has emerged as a noteworthy and eco-friendly methodology. Keshtmand et al. (2023) underscored the significance of green-synthesized SeNPs, presenting a compelling avenue in this domain. This innovative strategy harnesses the potential of natural resources, such as plant extracts or microorganisms, to facilitate the production of SeNPs.

Characterizations of biogenic selenium nanoparticles and their anti-biofilm potential against Streptococcus mutans ATCC 25175

INTRODUCTION

S. mutans has been identified as the primary pathogenic bacterium in biofilm-mediated dental caries. The biogenic selenium nanoparticles (SeNPs) produced by L. plantarum KNF-5 were used in this study against S. mutans ATCC 25175.

OBJECTIVES

The aims of this study were: (1) the biosynthesis of SeNPs by L. plantarum KNF-5, (2) the characterization of SeNPs, (3) the investigation of the inhibitory effect of biogenic SeNPs against S. mutans ATCC 25175, and (4) the determination of the anti-biofilm potential of SeNPS against S. mutans ATCC 25175.

METHODOLOGY

3 mL of the culture was added to 100 mL of MRS medium and incubated. After 4 h, Na2SeO3 solution (concentration 100 μg/mL) was added and incubated at 37 °C for 36 h. The color of the culture solution changed from brownish-yellow to reddish, indicating the formation of SeNPs. The characterization of SeNPs was confirmed by UV-Vis spectrophotometry, FTIR, SEM-EDS and a particle size analyzer. The antibacterial activity was determined by the disk diffusion method, the MIC by the micro-double dilution method, and the biofilm inhibitory potential by the crystal violet method and the MTT assay. The effect of SeNPs on S. mutans ATCC 25175 was determined using SEM and CLSM spectrometry techniques. The sulfate-anthrone method was used to analyze the effect of SeNPs on insoluble extracellular polysaccharides. The expression of genes in S. mutans ATCC 25175 was analyzed by real-time quantitative polymerase chain reaction (RT-qPCR).

PREPARATION OF NANOPARTICLES

SeNPs produced by probiotic bacteria are considered a safe method. In this study, L. plantarum KNF-5 (probiotic strain) was used for the production of SeNPs.

RESULTS

The biogenic SeNPs were spherical and coated with proteins and polysaccharides and had a diameter of about 270 nm. The MIC of the SeNPs against S. mutans ATCC 25175 was 3.125 mg/mL. Biofilm growth was also significantly suppressed at this concentration. The expression of genes responsible for biofilm formation (GtfB, GtfC, BrpA and GbpB,) was reduced when S. mutans ATCC 25175 was treated with SeNPs.

CONCLUSION

It was concluded that the biogenic SeNPs produced by L. plantarum KNF-5 was highly effective to inhibit the growth of S. mutans ATCC 25175.

NOVELTY STATEMENT

The application of biogenic SeNPs, a natural anti-biofilm agent against S. mutans ATCC 25175. In the future, this study will provide a new option for the prevention and treatment of dental caries.

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.

Selenium-Enriched E. coli Bacteria Mitigate the Age-Associated Degeneration of Cholinergic Neurons in C. elegans

Selenium (Se) is an essential trace element for humans and animals, but high-dose supplementation with Se compounds, most notably selenite, may exert cytotoxic and other adverse effects. On the other hand, bacteria, including Escherichia coli (E. coli), are capable of reducing selenite to red elemental Se that may serve as a safer Se source. Here, we examined how a diet of Se-enriched E. coli bacteria affected vital parameters and age-associated neurodegeneration in the model organism Caenorhabditis elegans (C. elegans). The growth of E. coli OP50 for 48 h in medium supplemented with 1 mM sodium selenite resulted in reddening of the bacterial culture, accompanied by Se accumulation in the bacteria. Compared to nematodes supplied with the standard E. coli OP50 diet, the worms fed on Se-enriched bacteria were smaller and slimmer, even though their food intake was not diminished. Nevertheless, given the choice, the nematodes preferred the standard diet. The fecundity of the worms was not affected by the Se-enriched bacteria, even though the production of progeny was somewhat delayed. The levels of the Se-binding protein SEMO-1, which serves as a Se buffer in C. elegans, were elevated in the group fed on Se-enriched bacteria. The occurrence of knots and ruptures within the axons of cholinergic neurons was lowered in aged nematodes provided with Se-enriched bacteria. In conclusion, C. elegans fed on Se-enriched E. coli showed less age-associated neurodegeneration, as compared to nematodes supplied with the standard diet.

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.

Superoxide Dismutase Catalyzed Size-Adjustable Selenium Nanoparticles in Saccharomyces boulardii

Selenium nanoparticles (SeNPs) are important and safe food and feed additives that can be used for dietary supplementation. In this study, a mutagenic strain of Saccharomyces boulardii was employed to obtain biologically synthesized SeNPs (BioSeNPs) with the desired particle size by controlling the dosage and duration of sodium selenite addition, and the average particle size achieved was 55.8 nm with protease A encapsulation. Transcriptomic analysis revealed that increased expression of superoxide dismutase 1 (SOD1) in the mutant strain effectively promoted the synthesis of BioSeNPs and the formation of smaller nanoparticles. Under sodium selenite stress, the mutant strain exhibited significantly increased expression of glutathione peroxidase 2 (GPx2), which was significantly greater in the mutant strain than in the wild type, facilitating the synthesis of glutathione selenol and providing abundant substrates for the production of BioSeNPs. Furthermore, based on the experimental results and transcriptomic analysis of relevant genes such as sod1, gpx2, the thioredoxin reductase 1 gene (trr1) and the thioredoxin reductase 2 gene (trr2), a yeast model for the size-controlled synthesis of BioSeNPs was constructed. This study provides an important theoretical and practical foundation for the green synthesis of controllable-sized BioSeNPs or other metal nanoparticles with potential applications in the fields of food, feed, and biomedicine.

Synthesis, characterization, biological activity, and in vitro digestion of selenium nanoparticles stabilized by Antarctic ice microalgae polypeptide

A new type of uniformly dispersed selenium nanoparticles (SeNPs) was prepared using Antarctic ice microalgae polypeptides (AIMP) as the stabilizer and dispersant. Different characterization techniques and tests show that the SeNPs are effectively combined with AIMP through physical adsorption and hydrogen bonding to form a more stable structure. Orange-red, zero-valence, amorphous, and spherical AIMP-SeNPs with a diameter of 52.07 ± 1.011 nm and a zeta potential of -41.41 ± 0.882 mV were successfully prepared under the optimal conditions. The AIMP-SeNPs had significantly higher DPPH, ABTS and hydroxyl radicals scavenging abilities compared with AIMP and Na2SeO3, and prevented the growth of both Gram-negative and Gram-positive bacteria by disrupting the integrity of cell walls, cell membranes and mitochondrial membranes. The AIMP-SeNPs had higher gastrointestinal stability compared with SeNPs. Thus, this research highlights the crucial role of AIMP as a biopolymer framework in the dispersion, stabilization, and size management of SeNPs and concludes that AIMP-SeNPs can be exploited as a potent antioxidant supplement and antibacterial substance in foods and medicine.

Catechins and Selenium Species-How They React with Each Other

The combination of selenium and tea infusion, both with antioxidant properties, has potentially complementary mechanisms of action. Se-enriched tea has been considered as a possible Se supplement and a functional beverage to reduce the health risk of Se deficiency. This work investigated the interactions between plant catechins present in tea infusions and selenium species based on changes in the concentration of both reagents, their stability in aqueous solutions, and the possibilities of selenonanoparticles (SeNPs) formation. Selenium species exhibited instability both alone in their standard solutions and in the presence of studied catechins; selenocystine appeared as the most unstable. The recorded UV-Vis absorption spectra indicated the formation of SeNPs in the binary mixtures of catechins and selenite. SeNPs have also formed with diameters smaller than 100 nm when selenite and selenomethionine were added to tea infusions. This is an advantage from the point of view of potential medical applications.