Abstract
Selenium nanoparticles (Se-NPs) were synthesized by green technology using the bacterial isolate Pseudomonas aeruginosa strain JS-11. The bacteria exhibited significant tolerance to selenite (SeO3 2−) up to 100 mM concentration with an EC50 value of 140 mM. The spent medium (culture supernatant) contains the potential of reducing soluble and colorless SeO3 2− to insoluble red elemental selenium (Se0) at 37°C. Characterization of red Se° product by use of UV-Vis spectroscopy, X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM) with energy dispersive X-ray spectrum (EDX) analysis revealed the presence of stable, predominantly monodispersed and spherical selenium nanoparticles (Se-NPs) of an average size of 21 nm. Most likely, the metabolite phenazine-1-carboxylic acid (PCA) released by strain JS-11 in culture supernatant along with the known redox agents like NADH and NADH dependent reductases are responsible for biomimetic reduction of SeO3 2− to Se° nanospheres. Based on the bioreduction of a colorless solution of SeO3 2− to elemental red Se0, a high throughput colorimetric bioassay (Se-Assay) was developed for parallel detection and quantification of nanoparticles (NPs) cytotoxicity in a 96 well format. Thus, it has been concluded that the reducing power of the culture supernatant of strain JS-11 could be effectively exploited for developing a simple and environmental friendly method of Se-NPs synthesis. The results elucidated that the red colored Se° nanospheres may serve as a biosensor for nanotoxicity assessment, contemplating the inhibition of SeO3 2− bioreduction process in NPs treated bacterial cell culture supernatant, as a toxicity end point.
Highlights
Selenium (Se0) is a trace element commonly found in materials of the earth’s crust, and belongs to group 16 of the periodic table
Studies based on X-ray absorption spectroscopy revealed that the soil bacterium Ralstonia metallidurans CH34, resistant to SeO322 is capable of its detoxification, and localize the red Seu granules mainly in the cytoplasm [18]
Sarret et al [19] investigated the kinetics of selenite and selenate accumulation and Se speciation to identify the chemical intermediates putatively appearing during reduction using X-ray absorption near-edge structure (XANES) spectroscopy
Summary
Selenium (Se0) is a trace element commonly found in materials of the earth’s crust, and belongs to group 16 (chalcogens) of the periodic table. Seu is well known for its photoelectric, semiconductor, free-radical scavenging, anti-oxidative and anti-cancer properties [1]. It occurs in different forms as red amorphous selenium (Se0), highly water soluble selenate (SeO422) and selenite (SeO322), and as gaseous selenide (Se22). The ability to reduce the toxic SeO422 and SeO322 species into non-toxic elemental form Seu has been demonstrated under aerobic and anaerobic conditions [5,6,7,8]. Studies based on X-ray absorption spectroscopy revealed that the soil bacterium Ralstonia metallidurans CH34, resistant to SeO322 is capable of its detoxification, and localize the red Seu granules mainly in the cytoplasm [18]. There are few reports in literature on the aerobic formation of Se-NPs by microorganisms such as Pseudomonas aeruginosa, Bacillus sp. and Enterobacter cloacae [22,23,24]
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