Abstract
Selenite (SeO32−), the most toxic and most reactive selenium (Se) oxyanion, can be reduced to elemental selenium (Se0) nanoparticles by a variety of bacteria, including Enterococcus spp. Previously, the orthodox view held that the reduction of SeO32− to Se0 by a wide range of bacteria was solely accomplished by biological processes; however, recent studies have shown that various bacterial strains secrete metal-reducing metabolites, thereby indirectly catalysing the reduction of these metal species. In the current study, selenium nanoparticles were synthesised from the abiotic reduction of selenite with the use of Enterococcus spp. cell-free extract. Once separated from the cell-free extract, the particles were analysed using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Transmission electron microscopy (TEM) and a Zetasizer. The results revealed that the SeNPs were spherical in shape, containing both amorphous and crystalline properties, and the sizes with the highest frequency ranged close to 200 nm. Additionally, the obtained nanoparticles exhibited antimicrobial properties by directly inhibiting the viability of an E. coli bacterial strain. The results demonstrate not only the potential of abiotic production of SeNPs, but also the potential for these particles as microbial inhibitors in medical or similar fields.
Highlights
Academic Editor: Elena IvanovaThe emergence of nanotechnology in science and technology in recent years has dramatically transformed various industries
We propose the use of an abiotic system to circumvent this problem, as the nanoparticles can be synthesised in a cell-free extract, viz. a medium that initially contained active biomass which was subsequently removed, leaving active water-soluble biomolecules in solution
The antibacterial properties of the prepared nanoparticle samples were tested on the The antibacterial properties of the prepared nanoparticle samples were tested on the gram-negative E. coli bacterial strain obtained from a study which focused on chromium gram-negative E. coli bacterial strain obtained from a study which focused on chromium reduction [24]
Summary
The emergence of nanotechnology in science and technology in recent years has dramatically transformed various industries. There are a number of microbial species which are able to reduce selenite to elemental selenium as nanoparticles, but most of these utilise intracellular processes for SeNP production. Separating the intracellular nanoparticles from biomass for the purpose of selenium recovery can be achieved through processes such as cell lysis followed by filtration or centrifugation [20]. These processes are very energy-intensive and involve significant amounts of chemicals that can lead to further environmental contamination [21]. A medium that initially contained active biomass which was subsequently removed, leaving active water-soluble biomolecules in solution This process eliminates the requirement for separation of the selenium nanoparticles from the bacterial biomass altogether. The second objective is to characterise the nanoparticles produced and explore possible applications by assessing how these inhibit a strain of the common food pathogen E. coli
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