Proteins enriched in charged amino acids control the formation and stabilization of selenium nanoparticles in Comamonas testosteroni S44

Identification and Functional Characterization of a Surfactant-like Protein Region in Flagellin FliC for Stabilizing Selenium Nanoparticles and Enhancing Bioavailability

Biogenic selenium nanoparticles (SeNPs) are the most favorable Se form for nutritional supplementation due to their high stability, low toxicity, and high activity. However, the interaction between the surface-binding proteins and their stable biogenic SeNPs, as well as their impact on the stability and bioavailability of SeNPs, remains to be understood. In vitro stabilization experiments revealed an amino acid segment (F(235-386)) in Rahnella aquatilis' flagellin FliC, with surfactant-like properties, stabilizing SeNPs under harsh conditions. FliC and F(235-386) were employed as stabilizers to synthesize SeNPs (FliC@SeNPs and F(235-386)@SeNPs), and surface chemistry analysis revealed coordination reactions between the proteins and Se atoms on the surface of SeNPs. Both FliC and F(235-386) enhanced SeNPs uptake in wheat seedlings but reduced it in bacteria and yeast. This study highlights FliC's core function in stabilizing SeNPs and enhancing their bioavailability, paving the way for agricultural and nutritional applications.

A State-of-the-Art Systemic Review on Selenium Nanoparticles: Mechanisms and Factors Influencing Biogenesis and Its Potential Applications

Selenium is a trace element required for the active function of numerous enzymes and various physiological processes. In recent years, selenium nanoparticles draw the attention of scientists and researchers because of its multifaceted uses. The process involved in chemically synthesized SeNPs has been found to be hazardous in nature, which has paved the way for safe and ecofriendly SeNPs to be developed in order to achieve sustainability. In comparison to chemical synthesis, SeNPs can be synthesized more safely and with greater flexibility utilizing bacteria, fungi, and plants. This review focused on the synthesis of SeNPs utilizing bacteria, fungi, and plants; the mechanisms involved in SeNP synthesis; and the effect of various abiotic factors on SeNP synthesis and morphological characteristics. This article discusses the synergies of SeNP synthesis via biological routes, which can help future researchers to synthesize SeNPs with more precision and employ them in desired fields.

Selenite bioreduction with concomitant green synthesis of selenium nanoparticles by a selenite resistant EPS and siderophore producing terrestrial bacterium

Environmental bacterial isolates play a very important role in bioremediation of metals and toxic metalloids. A bacterial strain with high selenite (SeO32-) tolerance and reducing capability was isolated from electronic waste dump site in Banaras Hindu University, Varanasi, India. Based on 16 S rRNA sequencing and BLAST search, this bacterial isolate was identified as Bacillus paramycoides and designated as strain MF-14. It tolerated Sodium selenite up to 110 mM when grown aerobically in LB broth and reduced selenite into elemental selenium (Se0) significantly within 24 h with concomitant biosynthesis of selenium nanoparticles as clearly revealed by brick red precipitate and specific surface plasmon resonance peak at 210 nm using UV-Visible spectrophotometer. Scanning electron microscopy (SEM) analysis of this bacterial strain exposed to 1mM and 5 mM selenite also demonstrated morphological alterations as cell enlargement due to accumulation and bioprecipitation of elemental selenium (Se0). The FTIR analysis clearly demonstrated that functional groups present on the surface of biogenic selenium nanoparticles (SeNPs) play a significant role in the stabilization and capping of SeNPs. Furthermore, these SeNPs were characterized using spectroscopic analysis involving Dynamic light scattering, zeta potential, XPS, FTIR, XRD and Raman spectroscopy which clearly revealed particle size 10-700 nm, amorphous nature, stability as well as it's oxidation state. The biochemical studies have demonstrated that membrane bound reductase enzyme may be responsible for significant reduction of selenite into elemental selenium. Therefore, we may employ Bacillus paramycoides strain MF-14 successfully for bioremediation of selenite contaminated environmental sites with concomitant green synthesis of SeNPs.

Potential Self-Attenuation of Arsenic by Indigenous Microorganisms in the Nakdong River

The toxic element arsenic (As) has become the major focus of global research owing to its harmful effects on human health, resulting in the establishment of several guidelines to prevent As contamination. The widespread industrial use of As has led to its accumulation in the environment, increasing the necessity to develop effective remediation technologies. Among various treatments, such as chemical, physical, and biological treatments, used to remediate As-contaminated environments, biological methods are the most economical and eco-friendly. Microbial oxidation of arsenite (As(III)) to arsenate (As(V)) is a primary detoxification strategy for As remediation as it reduces As toxicity and alters its mobility in the environment. Here, we evaluated the self-detoxification potential of microcosms isolated from Nakdong River water by investigating the autotrophic and heterotrophic oxidation of As(III) to As(V). Experimental data revealed that As(III) was oxidized to As(V) during the autotrophic and heterotrophic growth of river water microcosms. However, the rate of oxidation was significantly higher under heterotrophic conditions because of the higher cell growth and density in an organic-matter-rich environment compared to that under autotrophic conditions without the addition of external organic matter. At an As(III) concentration > 5 mM, autotrophic As(III) oxidation remained incomplete, even after an extended incubation time. This inhibition can be attributed to the toxic effect of the high contaminant concentration on bacterial growth and the acidification of the growth medium with the oxidation of As(III) to As(V). Furthermore, we isolated representative pure cultures from both heterotrophic- and autotrophic-enriched cultures. The new isolates revealed new members of As(III)-oxidizing bacteria in the diversified bacterial community. This study highlights the natural process of As attenuation within river systems, showing that microcosms in river water can detoxify As under both organic-matter-rich and -deficient conditions. Additionally, we isolated the bacterial strains HTAs10 and ATAs5 from the microcosm which can be further investigated for potential use in As remediation systems. Our findings provide insights into the microbial ecology of As(III) oxidation in river ecosystems and provide a foundation for further investigations into the application of these bacteria for bioremediation.

Time-Resolved Examination of Fungal Selenium Redox Transformations

Selenium (Se) is both a micronutrient required for most life and an element of environmental concern due to its toxicity at high concentrations, and both bioavailability and toxicity are largely influenced by the Se oxidation state. Environmentally relevant fungi have been shown to aerobically reduce Se(IV) and Se(VI), the generally more toxic and bioavailable Se forms. The goal of this study was to shed light on fungal Se(IV) reduction pathways and biotransformation products over time and fungal growth stages. Two Ascomycete fungi were grown with moderate (0.1 mM) and high (0.5 mM) Se(IV) concentrations in batch culture over 1 month. Fungal growth was measured throughout the experiments, and aqueous and biomass-associated Se was quantified and speciated using analytical geochemistry, transmission electron microscopy (TEM), and synchrotron-based X-ray absorption spectroscopy (XAS) approaches. The results show that Se transformation products were largely Se(0) nanoparticles, with a smaller proportion of volatile, methylated Se compounds and Se-containing amino acids. Interestingly, the relative proportions of these products were consistent throughout all fungal growth stages, and the products appeared stable over time even as growth and Se(IV) concentration declined. This time-series experiment showing different biotransformation products throughout the different growth phases suggests that multiple mechanisms are responsible for Se detoxification, but some of these mechanisms might be independent of Se presence and serve other cellular functions. Knowing and predicting fungal Se transformation products has important implications for environmental and biological health as well as for biotechnology applications such as bioremediation, nanobiosensors, and chemotherapeutic agents.

Investigation of the Effect of Dispersion Medium Parameters on the Aggregative Stability of Selenium Nanoparticles Stabilized with Catamine AB

This article presents the results of the synthesis of Se NPs stabilized by a quaternary ammonium compound-catamine AB. Se NPs were obtained by chemical reduction in an aqueous medium. In the first stage of this study, the method of synthesis of Se NPs was optimized by a multifactorial experiment. The radius of the obtained samples was studied by dynamic light scattering, and the electrokinetic potential was studied using acoustic and electroacoustic spectrometry. Subsequently, the samples were studied by transmission electron microscopy, and the analysis of the data showed that a bimodal distribution is observed in negatively charged particles, where one fraction is represented by spheres with a diameter of 45 nm, and the second by 1 to 10 nm. In turn, positive Se NPs have a diameter of about 70 nm. In the next stage, the influence of the active acidity of the medium on the stability of Se NPs was studied. An analysis of the obtained data showed that both sols of Se NPs exhibit aggregative stability in the pH range from 2 to 6, while an increase in pH to an alkaline medium is accompanied by a loss of particle stability. Next, we studied the effect of ionic strength on the aggregative stability of Se NPs sols. It was found that negatively charged ions have a significant effect on the particle size of the positive sol of Se NPs, while the particle size of the negative sol is affected by positively charged ions.

Biogenic selenium nanoparticles with antifungal activity against the wood-rotting fungus Oligoporus pelliculosus

Selenium nanoparticles (SeNPs) have antimicrobial and antifungal activity. SeNPs using Se resistant bacteria is a low cost and eco-friendly technology. Fungal contamination of wood during drying is one of the main causes of economic losses in the wood industry. The bacterium Delftia sp. 5 resistance to Se and its ability to produce SeNPs able to inhibit the growth of the wood brown-rotting fungus Oligoporus pelliculosus was analyzed. The strain showed an optimal SeNPs production when selenite concentration was 160 mg L ^-1. The SeNPs were spherical with an average size 192.33 ± 8.6 nm and a zeta potential of -41.4 ± 1.3 nm. The SeNPs produced by Delftia sp. 5 (33.6 ± 0.1 mg L ^-1 Se) inhibited the growth of O. pelliculosus in agar plates and in Nothofagus pumilio (Lenga) wood samples. Delftia sp. 5 SeNPs could be used for embedding lenga wood prior to drying for preventing the growth of the deteriorating fungi O. pelliculosus.

Treatments of Mycobacterium tuberculosis and Toxoplasma gondii with Selenium Nanoparticles

Toxoplasma gondii and Mycobacterium tuberculosis are pathogens that are harmful to humans. When these diseases interact in humans, the result is typically fatal to the public health. Several investigations on the relationship between M. tuberculosis and T. gondii infections have found that there is a strong correlation between them with each infection having a reciprocal effect on the other. TB may contribute to the reactivation of innate toxoplasmosis or enhance susceptibility to a new infection, and toxoplasma co-infection may worsen the severity of pulmonary tuberculosis. As a consequence, there is an earnest and urgent necessity to generate novel therapeutics that can subdue these challenges. Selenium nanostructures' compelling properties have been shown to be a successful treatment for Mycobacterium TB and Toxoplasma gondii. Despite the fact that selenium (Se) offers many health advantages for people, it also has a narrow therapeutic window; therefore, consuming too much of either inorganic or organic compounds based on selenium can be hazardous. Compared to both inorganic and organic Se, Se nanoparticles (SeNPs) are less hazardous. They are biocompatible and excellent in selectively targeting specific cells. As a consequence, this review conducted a summary of the efficacy of biogenic Se NPs in the treatment of tuberculosis (TB) and toxoplasmosis. Mycobacterium tuberculosis, Toxoplasma gondii, and their co-infection were all briefly described.

Synthesis and characterization of selenium nanoparticles stabilized with cocamidopropyl betaine

In this work, selenium nanoparticles (Se NPs) stabilized with cocamidopropyl betaine were synthesized for the first time. It was observed that Se NPs synthesized in excess of selenic acid had a negative charge with ζ-potential of -21.86 mV, and in excess of cocamidopropyl betaine-a positive charge with ξ =  + 22.71 mV. The resulting Se NPs with positive and negative charges had a spherical shape with an average size of about 20-30 nm and 40-50 nm, respectively. According to the data of TEM, HAADF-TEM using EDS, IR spectroscopy and quantum chemical modeling, positively charged selenium nanoparticles have a cocamidopropylbetaine shell while the potential- forming layer of negatively charged selenium nanoparticles is formed by SeO₃^2- ions. The influence of various ions on the sol stability of Se NPs showed that SO₄^2- and PO₄^3- ions had an effect on the positive Se NPs, and Ba²⁺ and Fe³⁺ ions had an effect on negative Se NPs, which corresponded with the Schulze-Hardy rule. The mechanism of coagulating action of various ions on positive and negative Se NPs was also presented. Also, influence of the active acidity of the medium on the stability of Se NPs solutions was investigated. Positive and negative sols of Se NPs had high levels of stability in the considered range of active acidity of the medium in the range of 1.21-11.98. Stability of synthesized Se NPs stability has been confirmed in real system (liquid soap). An experiment with the addition of Se NPs stabilized with cocamidopropyl betaine to liquid soap showed that the particles of dispersed phases retain their initial distributions, which revealed the stability of synthesized Se NPs.

Mitigation of the salinity stress in rapeseed (Brassica napus L.) productivity by exogenous applications of bio-selenium nanoparticles during the early seedling stage

In recent years, much attention has been directed toward using nanoparticles (NPs) as one of the most effective strategies to improve plant growth, especially under salt stress conditions. Further research has been conducted to develop NPs using various chemical ways; accordingly, knowledge about the beneficial effect of bioSeNPs in rapeseed is obscure. Selenium (Se) is a vital micronutrient with a series of physiological and antioxidative properties. Seed priming is emerging as a low-cost, efficient, and environment-friendly seed treatment in nanotechnology. The current study was carried out to examine the promising effects of nanopriming via bioSeNPs on the expression level of aquaporin genes, seed microstructure, seed germination, growth traits, physiochemical attributes, and minerals uptake of two rapeseed cultivars under salinity stress conditions. Our investigation monitored the positive effects of bioSeNPs on the expression level of aquaporin genes (BnPIP1-1 and BnPIP2-1) and water uptake during the seed imbibition (4 and 8 h of priming), which indicated higher imbibition potential and germination promotion with bioSeNPs application (most effective at 150 μmol/L). The total performance index was significantly enhanced with nano-treatments in rapeseed seedlings. Collectively, nano-application improved seed microstructure, seed germination, and photosynthetic efficiency directly correlated with higher seedlings biomass, especially with a higher concentration of bioSeNPs. The enhancement in α-amylase and free amino acid contents in nanoprimed seeds resulted in rapid seed germination. Moreover, bioSeNPs increased the osmotic adjustment and enhanced the efficiency of the plant's defense system by improving the activity of enzymatic and non-enzymatic antioxidants, thus enhancing ROS scavenging under salt stress. The obtained results may indicate the strengthening of seed vigor, improving seedling growth and physiochemical attributes via bioSeNPs. Our findings displayed that bioSeNPs modulated the Na⁺ and K⁺ uptake, which improved the rapeseed growth and showed a close relationship with the low contents of toxic Na⁺ ion; thus, it prevented oxidative damage due to salt stress. This comprehensive data can add more knowledge to understand the mechanisms behind plant-bioSeNPs interaction and provide physiological evidence for the beneficial roles of nanopriming using bioSeNPs on rapeseed germination and seedling development under salinity stress conditions. Such studies can be used to develop simple prepackaged nano primer products, which can be used before sowing to boost seed germination and crop productivity under stress conditions.

Comparative efficacy of bio-selenium nanoparticles and sodium selenite on morpho-physiochemical attributes under normal and salt stress conditions, besides selenium detoxification pathways in Brassica napus L

Selenium nanoparticles (SeNPs) have attracted considerable attention globally due to their significant potential for alleviating abiotic stresses in plants. Accordingly, further research has been conducted to develop nanoparticles using chemical ways. However, our knowledge about the potential benefit or phytotoxicity of bioSeNPs in rapeseed is still unclear. Herein, we investigated the effect of bioSeNPs on growth and physiochemical attributes, and selenium detoxification pathways compared to sodium selenite (Se (IV)) during the early seedling stage under normal and salt stress conditions. Our findings showed that the range between optimal and toxic levels of bioSeNPs was wider than Se (IV), which increased the plant’s ability to reduce salinity-induced oxidative stress. BioSeNPs improved the phenotypic characteristics of rapeseed seedlings without the sign of toxicity, markedly elevated germination, growth, photosynthetic efficiency and osmolyte accumulation versus Se (IV) under normal and salt stress conditions. In addition to modulation of Na⁺ and K⁺ uptake, bioSeNPs minimized the ROS level and MDA content by activating the antioxidant enzymes engaged in ROS detoxification by regulating these enzyme-related genes expression patterns. Importantly, the main effect of bioSeNPs and Se (IV) on plant growth appeared to be correlated with the change in the expression levels of Se-related genes. Our qRT-PCR results revealed that the genes involved in Se detoxification in root tissue were upregulated upon Se (IV) treated seedlings compared to NPs, indicating that bioSeNPs have a slightly toxic effect under higher concentrations. Furthermore, bioSeNPs might improve lateral root production by increasing the expression level of LBD16. Taken together, transamination and selenation were more functional methods of Se detoxification and proposed different degradation pathways that synthesized malformed or deformed selenoproteins, which provided essential mechanisms to increase Se tolerance at higher concentrations in rapeseed seedlings. Current findings could add more knowledge regarding the mechanisms underlying bioSeNPs induced plant growth.

Microbial reduction and resistance to selenium: Mechanisms, applications and prospects

Selenium is an essential trace element for humans, animals and microorganisms. Microbial transformations, in particular, selenium dissimilatory reduction and bioremediation applications have received increasing attention in recent years. This review focuses on multiple Se-reducing pathways under anaerobic and aerobic conditions, and the phylogenetic clustering of selenium reducing enzymes that are involved in these processes. It is emphasized that a selenium reductase may have more than one metabolic function, meanwhile, there are several Se(VI) and/or Se(IV) reduction pathways in a bacterial strain. It is noted that Se(IV)-reducing efficiency is inconsistent with Se(IV) resistance in bacteria. Moreover, we discussed the links of selenium transformations to biogeochemical cycling of other elements, roles of Se-reducing bacteria in soil, plant and digestion system, and the possibility of using functional genes involved in Se transformation as biomarker in different environments. In addition, we point out the gaps and perspectives both on Se transformation mechanisms and applications in terms of bioremediation, Se fortification or dietary supplementation.

Selenium and zinc oxide nanoparticles modulate the molecular and morpho-physiological processes during seed germination of Brassica napus under salt stress

The advent of the nanotechnology era offers a unique opportunity for sustainable agriculture, and the contribution of nanoparticles (NPs) to ameliorate abiotic stresses became the new area of interest for researchers due to their special physiochemical characteristics in the biological system. Salinity is a key devastating abiotic factor that hinders the development and yield of rapeseed. On the flip side, the impact of nanoparticles on plant hormones upon salt stress during seed imbibition and germination has been poorly understood. Hence, we aimed to study the influence of nanopriming on plant hormones and germination processes using selenium and zinc oxide nanoparticles (SeNPs and ZnONPs) during seed imbibition and the early seedling stage upon salinity stress. Nanopriming showed a positive effect on final germination percentage, germination rate, seed microstructure, and antioxidant enzyme activity of two rapeseed cultivars under salt stress. Moreover, nano-treatment decreased the expression of abscisic acid related genes BnCYP707A1, 3, and 4 during the priming time and after sowing, where the levels of BnCYP707A1, and 3 genes showed a slightly significant difference between the nanopriming and hydropriming, which gave an evidence that the nanopriming influenced the ABA levels then elevated the seed germination with SeNPs and ZnONPs. Likewise, nanoparticles significantly elevated the expression levels of BnGA20ox, BnGA3ox and BnCPS genes during the germination stage, especially at 24 h after being sown in salt stress. That confirms the positive role of SeNPs and ZnONPs in regulating gibberellic acid level, which increases the germination in primed seeds as compared to unprimed seeds and hydroprimed seeds. Additionally, our results demonstrated that nanopriming regulated the expression level of BnCAM and BnPER during priming time and after sowing, along with the various levels of expression remarkably in BnEXP4 and BnRAB28, especially at 24 h of being sown under salt stress, which promoted seed germination and early seedling growth. Overall, this work provides new insights into mechanisms underlying the interactions of SeNPs and ZnONPs with plant hormones during the seed imbibition and early seedling stage, consequently enhanced plant growth and development. Additionally, these findings portrayed that the application of SeNPs and ZnONPs could be a new strategy and useful approach to enhance tolerance against salinity in rapeseed plants.

Delineation of cellular stages and identification of key proteins for reduction and biotransformation of Se(IV) by Stenotrophomonas bentonitica BII-R7

The widespread use of selenium (Se) in technological applications (e.g., solar cells and electronic devices) has led to an accumulation of this metalloid in the environment to toxic levels. The newly described bacterial strain Stenotrophomonas bentonitica BII-R7 has been demonstrated to reduce mobile Se(IV) to Se(0)-nanoparticles (Se(0)NPs) and volatile species. Amorphous Se-nanospheres are reported to aggregate to form crystalline nanostructures and trigonal selenium. We investigated the molecular mechanisms underlying the biotransformation of Se(IV) to less toxic forms using differential shotgun proteomics analysis of S. bentonitica BII-R7 grown with or without sodium selenite for three different time-points. Results showed an increase in the abundance of several proteins involved in Se(IV) reduction and stabilization of Se(0)NPs, such as glutathione reductase, in bacteria grown with Se(IV), in addition to many proteins with transport functions, including RND (resistance-nodulation-division) systems, possibly facilitating Se uptake. Notably proteins involved in oxidative stress defense (e.g., catalase/peroxidase HPI) were also induced by Se exposure. Electron microscopy analyses confirmed the biotransformation of amorphous nanospheres to trigonal Se. Overall, our results highlight the potential of S. bentonitica in reducing the bioavailability of Se, which provides a basis both for the development of bioremediation strategies and the eco-friendly synthesis of biotechnological nanomaterials.

Selenite bioreduction and biosynthesis of selenium nanoparticles by Bacillus paramycoides SP3 isolated from coal mine overburden leachate

A native strain of Bacillus paramycoides isolated from the leachate of coal mine overburden rocks was investigated for its potential to produce selenium nanoparticles (SeNPs) by biogenic reduction of selenite, one of the most toxic forms of selenium. 16S rDNA sequencing was used to identify the bacterial strain (SP3). The SeNPs were characterized using spectroscopic (UV-Vis absorbance, dynamic light scattering, X-ray diffraction, and Raman), surface charge measurement (zeta potential), and ultramicroscopic (FESEM, EDX, FETEM) analyses. SP3 exhibited extremely high selenite tolerance (1000 mM) and reduced 10 mM selenite under 72 h to produce spherical monodisperse SeNPs with an average size of 149.1 ± 29 nm. FTIR analyses indicated exopolysaccharides coating the surface of SeNPs, which imparted a charge of -29.9 mV (zeta potential). The XRD and Raman spectra revealed the SeNPs to be amorphous. Furthermore, biochemical assays and microscopic studies suggest that selenite was reduced by membrane reductases. This study reports, for the first time, the reduction of selenite and biosynthesis of SeNPs by B. paramycoides, a recently discovered bacterium. The results suggest that B. paramycoides SP3 could be exploited for eco-friendly removal of selenite from contaminated sites with the concomitant biosynthesis of SeNPs.

Biogenic Selenium Nanoparticles: Potential Solution to Oxidative Stress Mediated Inflammation in Rheumatoid Arthritis and Associated Complications

Rheumatoid arthritis (RA) is a common chronic inflammation-mediated disorder having systematic complications. RA triggers a self-directed inflammatory and immunological cascade that culminates in joint destruction. Though a range of treatment options are available, none of them are without adverse effects and this has led researchers to search for alternative solutions. Nanomedicine has emerged as a powerful therapeutic alternative, and selenium (Se) is an essential micronutrient trace element that has a crucial role in human health and disease. Selenium nanoparticles (SeNPs) derived from biological sources, such as plants, bacteria, fungi, and proteins, have exhibited remarkable candidate properties and toxicological profiles, and hence have shown potential to be used as antirheumatic agents. The potential of SeNPs can be attributed to the effect of functional groups bound to them, concentration, and most importantly to their nano range size. The antirheumatic effect of SeNPs is considerable due to its potential in amelioration of oxidative stress-mediated inflammation via downregulation of radical and nonradical species, markers of inflammation, and upregulation of inherent antioxidant defenses. The size and concentration impact of SeNPs has been shown in the subsequent antioxidant and anti-inflammatory properties. Moreover, the article emphasizes the role of these biogenic SeNPs as a notable option in the nanomedicine arena that needs to be further studied as a prospective remedial alternative to cure RA and medication-related adverse events.

Highly stable selenium nanoparticles: Assembly and stabilization via flagellin FliC and porin OmpF in Rahnella aquatilis HX2

Microorganisms play a critical role in the reduction of the more toxic selenite and selenate to the less toxic elemental selenium. However, the assembly process and stability of selenium nanoparticles (SeNPs) remain understudied. The plant growth-promoting rhizobacterium Rahnella aquatilis HX2 can reduce selenite to biogenic SeNPs (BioSeNPs). Two main proteins, namely flagellin FliC and porin OmpF were identified in the BioSeNPs. The fliC and ompF gene mutation experiments demonstrated that the FliC and OmpF could control the assembly of BioSeNPs in vivo. At the same time, the expressed and purified FliC and OmpF could control the assembly of SeNPs in vitro. BioSeNPs produced by R. aquatilis HX2 exhibited high stability under various ionic strengths, while the chemically synthesized SeNPs (CheSeNPs) showed a high level of aggregation. The in vitro experiments verified that FliC and OmpF could prevent the aggregation of the CheSeNPs under various ionic strengths. This work reports the preparation of highly stable BioSeNPs produced by strain R. aquatilis HX2 and verifies that FliC and OmpF both could control the assembly and stability of BioSeNPs. BioSeNPs with high stability could be suitable as nutritional supplement to remedy selenium deficiency and in nanomedicine applications.

Biological selenite removal and recovery of selenium nanoparticles by haloalkaliphilic bacteria isolated from the Nakdong River

Microbial selenite reduction has increasingly attracted attention from the scientific community because it allows the separation of toxic Se from waste sources with the concurrent recovery of Se nanoparticles, a multifunctional material in nanotechnology industries. In this study, four selenite-reducing bacteria, isolated from a river water sample, were found to reduce selenite by > 85% within 3 d of incubation, at ambient temperature. Among them, strain NDSe-7, belonging to genus Lysinibacillus, can reduce selenite and produce Se nanospheres in alkaline conditions, up to pH 10.0, and in salinity of up to 7.0%. This strain can reduce 80 mg/L of selenite to elemental Se within 24 h at pH 6.0-8.0, at a temperature of 30-40 °C, and salinity of 0.1-3.5%. Strain NDSe-7 exhibited potential for use in Se removal and recovery from industrial saline wastewater with high alkalinity. This study indicates that extremophilic microorganisms for environmental remediation can be found in a conventional environment.

Biogenic Selenium Nanoparticles: A Fine Characterization to Unveil Their Thermodynamic Stability

Among the plethora of available metal(loid) nanomaterials (NMs), those containing selenium are interesting from an applicative perspective, due to their high biocompatibility. Microorganisms capable of coping with toxic Se-oxyanions generate mostly Se nanoparticles (SeNPs), representing an ideal and green alternative over the chemogenic synthesis to obtain thermodynamically stable NMs. However, their structural characterization, in terms of biomolecules and interactions stabilizing the biogenic colloidal solution, is still a black hole that impairs the exploitation of biogenic SeNP full potential. Here, spherical and thermodynamically stable SeNPs were produced by a metal(loid) tolerant Micrococcus sp. Structural characterization obtained by Scanning Electron Microscopy (SEM) revealed that these SeNPs were surrounded by an organic material that contributed the most to their electrosteric stabilization, as indicated by Zeta (ζ) potential measurements. Proteins were strongly adsorbed on the SeNP surface, while lipids, polysaccharides, and nucleic acids more loosely interacted with SeNMs as highlighted by Fourier Transform Infrared Spectroscopy (FTIR) and overall supported by multivariate statistical analysis. Nevertheless, all these contributors were fundamental to maintain SeNPs stable, as, upon washing, the NM-containing extract showed the arising of aggregated SeNPs alongside Se nanorods (SeNRs). Besides, Density Functional Theory (DFT) calculation unveiled how thiol-containing molecules appeared to play a role in SeO₃²⁻ bioreduction, stress oxidative response, and SeNP stabilization.

Selenium-Containing Polysaccharides—Structural Diversity, Biosynthesis, Chemical Modifications and Biological Activity

Selenosugars are a group of sugar derivatives of great structural diversity (e.g., molar masses, selenium oxidation state, and selenium binding), obtained as a result of biosynthesis, chemical modification of natural compounds, or chemical synthesis. Seleno-monosaccharides and disaccharides are known to be non-toxic products of the natural metabolism of selenium compounds in mammals. In the case of the selenium-containing polysaccharides of natural origin, their formation is also postulated as a form of detoxification of excess selenium in microorganisms, mushroom, and plants. The valency of selenium in selenium-containing polysaccharides can be: 0 (encapsulated nano-selenium), IV (selenites of polysaccharides), or II (selenoglycosides or selenium built into the sugar ring to replace oxygen). The great interest in Se-polysaccharides results from the expected synergy between selenium and polysaccharides. Several plant- and mushroom-derived polysaccharides are potent macromolecules with antitumor, immunomodulatory, antioxidant, and other biological properties. Selenium, a trace element of fundamental importance to human health, has been shown to possess several analogous functions. The mechanism by which selenium exerts anticancer and immunomodulatory activity differs from that of polysaccharide fractions, but a similar pharmacological effect suggests a possible synergy of these two agents. Various functions of Se-polysaccharides have been explored, including antitumor, immune-enhancement, antioxidant, antidiabetic, anti-inflammatory, hepatoprotective, and neuroprotective activities. Due to being non-toxic or much less toxic than inorganic selenium compounds, Se-polysaccharides are potential dietary supplements that could be used, e.g., in chemoprevention.

Potentialities of selenium nanoparticles in biomedical science

Selenium nanoparticles (SeNPs) have revolutionized biomedical domain and are still developing rapidly. Hence, this perspective elaborates SeNPs properties, synthesis, and biomedical applications, together with their potential for management of SARS-CoV-2.

Biomolecular composition of capping layer and stability of biogenic selenium nanoparticles synthesized by five bacterial species

Biogenic metal/metalloid nanoparticles of microbial origin retain a functional biomolecular capping layer that confers structural stability. Little is known about the composition of such capping material. In this study, selenium nanoparticles (SeNPs) synthesized by five different bacterial strains underwent comparative analysis with newly proposed protocols for quantifying the concentration of carbohydrates, proteins and lipids present in capping layers. SeNPs were therefore treated with two different detergents to remove portions of the surrounding caps in order to assess the resulting effects. Capping material quantification was carried out along with the measure of parameters such as hydrodynamic diameter, polydispersity and surface charge. SeNPs from the five strains showed differences in their distinct biomolecule ratios. On the other hand, structural changes in the nanoparticles induced by detergents did not correlate with the amounts of capping matrix removed. Thus, the present investigation suggests a hypothesis to describe capping layer composition of the bacterial SeNPs: some biomolecules are bound more strongly than others to the core metalloid matrix, so that the diverse capping layer components differentially contribute to the overall structural characteristics of the nanoparticles. Furthermore, the application of the approach here in combining quantification of cap-associated biomolecules with the measurement of structural integrity-related parameters can give the biogenic nanomaterial field useful information to construct a data bank on biogenically synthesized nanostructures.

Fungal Bioremediation of Selenium-Contaminated Industrial and Municipal Wastewaters

Selenium (Se) is an essential element for most organisms yet can cause severe negative biological consequences at elevated levels. The oxidized forms of Se, selenate [Se(VI)] and selenite [Se(IV)], are more mobile, toxic, and bioavailable than the reduced forms of Se such as volatile or solid phases. Thus, selenate and selenite pose a greater threat to ecosystems and human health. As current Se remediation technologies have varying efficiencies and costs, novel strategies to remove elevated Se levels from environments impacted by anthropogenic activities are desirable. Some common soil fungi quickly remove Se (IV and VI) from solution by aerobic reduction to solid or volatile forms. Here, we perform bench-scale culture experiments of two Se-reducing Ascomycota to determine their Se removal capacity in growth media conditions containing either Se(IV) or Se(VI) as well as in Se-containing municipal (∼25 μg/L Se) and industrial (∼2000 μg/L Se) wastewaters. Dissolved Se was measured throughout the experiments to assess Se concentration and removal rates. Additionally, solid-associated Se was quantified at the end of each experiment to determine the amount of Se removed to solid phases (e.g., Se(0) nanoparticles, biomass-adsorbed Se, or internal organic selenoproteins). Results show that under optimal conditions, fungi more efficiently remove Se(IV) from solution compared to Se(VI). Additionally, both fungi remove a higher percentage of Se from the filtered municipal wastewater compared to the industrial wastewater, though cultures in industrial wastewater retained a greater amount of solid-associated Se. Additional wastewater experiments were conducted with supplemental carbohydrate- or glycerin-based carbon products and additional nitrogen- and phosphorous-containing nutrients in some cases to enhance fungal growth. Relative to unamended wastewater experiments, supplemental carbohydrates promote Se removal from municipal wastewater but minimally impact industrial wastewater removal. This demonstrates that carbon availability and source impacts fungal Se reduction and removal from solution. Calculations to assess the leaching potential of solid-associated Se from fungal biomass show that wastewater Se release will not exceed regulatory limits. This study highlights the considerable potential for the mycoremediation of Se-contaminated wastewaters.

Developments in the study and applications of bacterial transformations of selenium species

Microbial bio-transformations of the essential trace element selenium are now recognized to occur among a wide variety of microorganisms. These transformations are used to convert this element into its assimilated form of selenocysteine, which is at the active center of a number of key enzymes, and to produce selenium nanoparticles, quantum dots, metal selenides, and methylated selenium species that are indispensable for biotechnological and bioremediation applications. The focus of this review is to present the state-of-the-art of all aspects of the investigations into the bacterial transformations of selenium species, and to consider the characterization and biotechnological uses of these transformations and their products.

Selenite reduction by the rhizobacterium Azospirillum brasilense, synthesis of extracellular selenium nanoparticles and their characterisation

Microbial reduction of selenium oxyanions has attracted attention in recent years. In this study, an original and simple method for the synthesis of extracellular selenium nanoparticles (Se NPs) of relatively uniform size has been developed using strains Sp7 and Sp245 of the ubiquitous plant-growth promoting rhizobacterium Azospirillum brasilense, both capable of selenite (SeO₃^2-) reduction. In addition, a reliable purification protocol for the recovery of the Se NPs has been perfected, which could be applied with minor modifications to cultures of other microbial species. Importantly, it was found that, by changing the conditions of bacterial reduction of selenite, extracellularly localised Se NPs can be obtained using bacteria which would otherwise produce intracellular Se NPs. In particular, bacterial cultures grown up to the end of the logarithmic growth phase, washed free of culture medium and then incubated with selenite, were used to obtain extracellular Se NPs. Their sizes depended on the initial selenite concentration (∼25-80 nm in diameter at 50-10 mM selenite, respectively). The Se NPs obtained were characterised by transmission electron microscopy (TEM), dynamic light scattering, as well as Raman and UV-vis spectroscopies. Their zeta potential was found to be negative (ca. minus 21-24 mV). Bacterial selenite reduction was also studied in the presence of the efflux pump inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP). In this case, TEM indicated the formation only of intracellular selenium crystallites. The data show that the formation of extracellular Se NPs requires normal bacterial metabolic activity, while CCCP evidently blocks the membrane export of Se⁰ nuclei.

Stability issues and approaches to stabilised nanoparticles based drug delivery system

Nanoparticles form the fundamental building blocks for many exciting applications in various scientific disciplines due to its unique features such as large surface to mass ratio, targeting potential, ability to adsorbed and carry other compound which makes them suitable for biomedical applications. However, the problem of the large-scale synthesis of nanoparticles remains challenging due to physical instability associated with nanoparticles which lead to generation of aggregates particles with high polydispersity index (PDI) indicating low particle homogeneity and eventually loss of their special nanoscale properties. The stabilisation concept can be generated by repulsive electrostatic force, which nanoparticles experience, when they are surrounded by a double layer of electric charges. Selection of proper stabiliser will govern the stability of NPs and ultimately development of optimised drug delivery system. This review summarises mechanism of physical instability issues likely to be encountered during the development of nanoformulations. It also discusses potential stabilising agents used so far and their mechanism in achieving stable nanosystems.

Kinetics of microbial selenite reduction by novel bacteria isolated from activated sludge

A total of three bacteria isolated from activated sludge of a wastewater treatment plant were found to reduce selenite to elemental selenium nanoparticles as both amorphous nanospheres and monoclinic nanocrystals. The three isolated strains, which are potential candidates for bioremediation of selenite-contaminated water sources, were designated as Citrobacter sp. NVK-2, Providencia sp. NVK-2A, and Citrobacter sp. NVK-6 based on 16S rRNA sequencing. Despite belonging to the same genus, the kinetics of selenite reduction by strain NVK-2 (V_max = 58.82 μM h^-1, K_m = 3737.12 μM) completely differed from that of strain NVK-6 (V_max = 19.23 μM h^-1, K_m = 1300.17 μM). The selenite reduction rate by strain NVK-2A (V_max = 9.26 μM h^-1, K_m = 3044.73 μM) was the slowest among the investigated microorganisms. The microbial selenite reduction rates according to various organic sources indicated that simple organic sources such as acetate and lactate were better than more complex organic sources such as propionate, butyrate, and glucose for selenite removal. Interestingly, the selenite reduction rate was significantly enhanced when the organic source was strategically divided into small portions and consecutively supplied to the culture.

Selenium as a pleiotropic agent for medical discovery and drug delivery

Selenium as a biologically active element lends much support to health maintenance and disease prevention. It is now presenting pleiotropic effects on therapy and drug delivery. In this study, a profiling on the physiological functions, therapeutic significances, clinical/preclinical performances, and biomedical and drug delivery applications of selenium in different modalities was carried out. Major interests focused on selenium-based nanomedicines in confronting various diseases pertaining to selenium or not, especially in antitumor and antidiabetes. Furthermore, the article exclusively discusses selenium nanoparticles featured by ameliorative functions with emphasis on their applications in medical practice and drug delivery. The state-of-the-art in medical discovery as well as research and development on selenium and nano-selenium is discussed in this review.

Selenium Analysis and Speciation in Dietary Supplements Based on Next-Generation Selenium Ingredients

Selenium is essential for humans and the deficit of Se requires supplementation. In addition to traditional forms such as Se salts, amino acids, or selenium-enriched yeast supplements, next-generation selenium supplements, with lower risk for excess supplementation, are emerging. These are based on selenium forms with lower toxicity, higher bioavailability, and controlled release, such as zerovalent selenium nanoparticles (SeNPs) and selenized polysaccharides (SPs). This article aims to focus on the existing analytical systems for the next-generation Se dietary supplement, providing, at the same time, an overview of the analytical methods available for the traditional forms. The next-generation dietary supplements are evaluated in comparison with the conventional/traditional ones, as well as the analysis and speciation methods that are suitable to reveal which Se forms and species are present in a dietary supplement. Knowledge gaps and further research potential in this field are highlighted. The review indicates that the methods of analysis of next-generation selenium supplements should include a step related to chemical species separation. Such a step would allow a proper characterization of the selenium forms/species, including molecular mass/dimension, and substantiates the marketing claims related to the main advantages of these new selenium ingredients.

Adsorption Removal of Multiple Dyes Using Biogenic Selenium Nanoparticles from an Escherichia coli Strain Overexpressed Selenite Reductase CsrF

Selenite reductase CsrF overexpressed Escherichia coli was used as a microbial factory to produce Se(0) nanoparticles (Bio-SeNPs). The Bio-SeNPs were characterized by transmission electronic microscopy, element mapping, scanning electron microscopy, energy-dispersive X-ray spectrographs, Zeta-potential, dynamic light scattering, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses. The results indicated that Bio-SeNPs are irregular spheres with diameters from 60 to105 nm and mainly consist of Se(0), proteins and lipids. Furthermore, it exhibited maximum adsorption capacity for anionic dye (congo red) at acidic pH and cationic dyes (safranine T and methylene blue) at alkaline pH. To gain more insight, adsorption kinetics, adsorption isotherms and adsorption thermodynamics studies were carried out. These results showed that the adsorption capacities of congo red, safranine T and methylene blue were 1577.7, 1911.0 and 1792.2 mg/g, respectively. These adsorption processes were spontaneous and primarily physical reactions. In addition, Bio-SeNPs can be effectively reused by 200 mmol/L NaCl. To the best of our knowledge, this is the first report of adsorption removal dyes by Bio-SeNPs. The adsorption capacities of Bio-SeNPs for congo red, safranine T and methylene blue were 6.8%, 25.2% and 49.0% higher than that for traditional bio-based materials, respectively.