Selenium Nanoparticle Synthesized by Proteus mirabilis YC801: An Efficacious Pathway for Selenite Biotransformation and Detoxification

Abstract

Selenite is extremely biotoxic, and as a result of this, exploitation of microorganisms able to reduce selenite to non-toxic elemental selenium (Se0) has attracted great interest. In this study, a bacterial strain exhibiting extreme tolerance to selenite (up to 100 mM) was isolated from the gut of adult Monochamus alternatus and identified as Proteus mirabilis YC801. This strain demonstrated efficient transformation of selenite into red selenium nanoparticles (SeNPs) by reducing nearly 100% of 1.0 and 5.0 mM selenite within 42 and 48 h, respectively. Electron microscopy and energy dispersive X-ray analysis demonstrated that the SeNPs were spherical and primarily localized extracellularly, with an average hydrodynamic diameter of 178.3 ± 11.5 nm. In vitro selenite reduction activity assays and real-time PCR indicated that thioredoxin reductase and similar proteins present in the cytoplasm were likely to be involved in selenite reduction, and that NADPH or NADH served as electron donors. Finally, Fourier-transform infrared spectral analysis confirmed the presence of protein and lipid residues on the surfaces of SeNPs. This is the first report on the capability of P. mirabilis to reduce selenite to SeNPs. P. mirabilis YC801 might provide an eco-friendly approach to bioremediate selenium-contaminated soil/water, as well as a bacterial catalyst for the biogenesis of SeNPs.

Influence of Bacterial Physiology on Processing of Selenite, Biogenesis of Nanomaterials and Their Thermodynamic Stability

“…The investigation conducted to unveil potential mechanism(s) exploited by MPV1 to cope with increasing concentrations of SeO 3 2− (0.5–10 mM) highlighted the growth and oxyanion removal rates (Figure 1a,b, Table 1) comparable to those described for most SeO 3 2− tolerant bacteria [3,29,30,31,32,33,34,35]. Since Se oxyanions exceeding 2.5 mM reappeared in the growth medium upon exposure to 3, 5, and 10 mM SeO 3 2− (Figure 1b, Table 1), 2.5 mM SeO 3 2− appears to be the threshold concentration biotically processed by MPV1 cells under these experimental conditions, as also observed in the case of Moraxella bovis [36].…”

“…Thus, the key role played by GSHs in MPV1 cells is to bioconvert Se oxyanions, yet ancillary enzymatic mechanism(s) can be induced as function of SeO 3 2− concentration and time of exposure. Ubiquitous enzymes, like NAD(P)H-dependent thioredoxin reductases and flavin oxidoreductases, sulfate or sulfite reductases, or fumarate reductases, were identified as responsible for the biotic reduction of high concentrations (from 2 to 10 mM) of SeO 3 2− [30,32,33,34,35,37]. In this regard, NADPH-dependent reduction activity toward high concentrations (5 mM) of SeO 3 2− was found in the cytoplasmic and, to a minor extent, in the periplasmic fractions of MPV1 cells [26].…”

“…Previous studies concerning the characterization of biogenic SeNSs showed the existence of an organic material playing a key role in their synthesis and stabilization [6,44]. Over the past few years, FTIR spectroscopy has been the most-used technique to assess the presence of biomolecules associated with SeNSs, enabling the detection of proteins, carbohydrates, and lipids within most of the extracts analyzed [20,32,37,47,51,52,53,54,55,56,57], including those recovered from MPV1 cells grown under optimal conditions [26]. Here, the detection of light elements attributable to biomolecules co-produced by the bacterial strain alongside Se (Table 4) highlighted a certain degree of variability among the biogenic NSs, likely due to the exploitation of multiple strategies by MPV1 to remove Se oxyanions [20,32].…”

“…Over the past few years, FTIR spectroscopy has been the most-used technique to assess the presence of biomolecules associated with SeNSs, enabling the detection of proteins, carbohydrates, and lipids within most of the extracts analyzed [20,32,37,47,51,52,53,54,55,56,57], including those recovered from MPV1 cells grown under optimal conditions [26]. Here, the detection of light elements attributable to biomolecules co-produced by the bacterial strain alongside Se (Table 4) highlighted a certain degree of variability among the biogenic NSs, likely due to the exploitation of multiple strategies by MPV1 to remove Se oxyanions [20,32]. The detection of N in some cases might be ascribed to the occurrence of proteins or metabolites within the biogenic extracts [26], whereas the constant presence of S signal may be due to the involvement of RSHs in SeO 3 2− bioprocessing for MPV1 cultures [20,21,58].…”

Microbial Mediated Synthesis of Silver Nanoparticles by Lactobacillus Plantarum TA4 and its Antibacterial and Antioxidant Activity

“…Earlier studies indicated that the fundamental mechanisms for the formation of AgNPs were facilitated by the enzyme nitrate reductase [7,39], which involved the transfer of electrons from nitrate to the metal group [40]. Likewise, Wang et al [41] reported that the reduction of selenium nanoparticles by Proteus mirabilis YC801 occurred by cytoplasmic enzymatic reduction involving thioredoxin reductase, glutathione reductase, or NADH-related reductase. On the other hand, Sintubin et al [11] discovered the biosynthesis of AgNPs through the interaction of Ag + with the functional groups present on the cell membrane of several Lactobacillus species.…”