Enterococcus spp. Cell-Free Extract: An Abiotic Route for Synthesis of Selenium Nanoparticles (SeNPs), Their Characterisation and Inhibition of Escherichia coli

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.

Synthesis and Assessment of Antimicrobial Composites of Ag Nanoparticles or AgNO3 and Egg Shell Membranes

“…The particle size distribution of the synthesized AgNPs is shown in Figure 2 . The data were analysed as per [ 54 ], and the results are summarized in Table 1 . It can be seen that the AgNPs exhibited a multi-modal distribution with an overall average particles size ( d 50 ) of 29.8 nm (Z-average particles size of 14.3 nm measured by the Zetasizer)—the discrepancy between the d 50 calculated from the distribution curves and the Z-average value relates to the limitations of the Zeta-sizer which requires that the sample be mono-modal, near-spherical particles, in a narrow size distribution [ 55 ].…”

Biological Selenite Reduction, Characterization and Bioactivities of Selenium Nanoparticles Biosynthesised by Pediococcus acidilactici DSM20284

“…The functional groups involved in the reduction of sodium selenite to SeNPs were evaluated by the Fourier transform infrared spectroscopy of all SeNPs synthesised. The spectrogram (Figure 7) suggests that macromolecules such as lipids, sugars, carbohydrates, nucleic acids, and especially proteins may be present to ensure the stability of abiotic SeNPs [32]. The peaks were between 4000 and 500 cm −1 .…”

Harnessing selenium nanoparticles (SeNPs) for enhancing growth and germination, and mitigating oxidative stress in Pisum sativum L.

“…When it comes to the Se species, selenite (SeO 3 2-) is its most toxic oxyanion 3 in addition to being highly reactive 4 . On the contrary, elemental Se (Se 0 ) is naturally insoluble, and it can form elemental Se nanoparticles (SeNPs) which have very good bioavailability 5 and display low toxicological potential 5,6 .Se is naturally occurring hence its interaction with plants through air, aquatic systems, and the soil is inevitable. Although it is essential for plant development, constant exposure to high Se concentrations leads to its accumulation in plants 7 .…”

“…) is its most toxic oxyanion 3 in addition to being highly reactive 4 . On the contrary, elemental Se (Se 0 ) is naturally insoluble, and it can form elemental Se nanoparticles (SeNPs) which have very good bioavailability 5 and display low toxicological potential 5,6 .…”

“…In this study, two methods were used to reduce selenite to elemental Se. Firstly, abiotically (abiotic-SeNPs) using secretions from a biological catalyst (Enterococcus species) as described by Tendenedzai et al 6 and secondly, by chemical means (chemical-SeNPs), using a reducing agent (L-ascorbic acid) as described by Shahabadi et al 28 . Once the nano-Se had been recovered, the effect of different concentrations of SeO 3 2− , abiotic-SeNPs, and chemical-SeNPs on the germination of P. sativum (pea seeds) was tested.…”