Physical–Chemical Properties of Biogenic Selenium Nanostructures Produced by Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1

Abstract

Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1 were isolated from the rhizosphere soil of the selenium-hyperaccumulator legume Astragalus bisulcatus and waste material from a dumping site for roasted pyrites, respectively. Here, these bacterial strains were studied as cell factories to generate selenium-nanostructures (SeNS) under metabolically controlled growth conditions. Thus, a defined medium (DM) containing either glucose or pyruvate as carbon and energy source along with selenite () was tested to evaluate bacterial growth, oxyanion bioconversion and changes occurring in SeNS features with respect to those generated by these strains grown on rich media. Transmission electron microscopy (TEM) images show extra- or intra-cellular emergence of SeNS in SeITE02 or MPV1 respectively, revealing the presence of two distinct biological routes of SeNS biogenesis. Indeed, the stress exerted by upon SeITE02 cells triggered the production of membrane vesicles (MVs), which surrounded Se-nanoparticles (SeNPsSeITE02-G_e and SeNPsSeITE02-P_e with average diameter of 179 ± 56 and 208 ± 60 nm, respectively), as highlighted by TEM and scanning electron microscopy (SEM), strongly suggesting that MVs might play a crucial role in the excreting mechanism of the SeNPs in the extracellular environment. On the other hand, MPV1 strain biosynthesized intracellular inclusions likely containing hydrophobic storage compounds and SeNPs (123 ± 32 nm) under pyruvate conditioning, while the growth on glucose as the only source of carbon and energy led to the production of a mixed population of intracellular SeNPs (118 ± 36 nm) and nanorods (SeNRs; average length of 324 ± 89). SEM, fluorescence spectroscopy, and confocal laser scanning microscopy (CLSM) revealed that the biogenic SeNS were enclosed in an organic material containing proteins and amphiphilic molecules, possibly responsible for the high thermodynamic stability of these nanomaterials. Finally, the biogenic SeNS extracts were photoluminescent upon excitation ranging from 380 to 530 nm, whose degree of fluorescence emission (λem = 416–640 nm) was comparable to that from chemically synthesized SeNPs with L-cysteine (L-cys SeNPs). This study offers novel insights into the formation, localization, and release of biogenic SeNS generated by two different Gram-negative bacterial strains under aerobic and metabolically controlled growth conditions. The work strengthens the possibility of using these bacterial isolates as eco-friendly biocatalysts to produce high quality SeNS targeted to possible biomedical applications and other biotechnological purposes.

Graphene Oxide Carboxymethylcellulose Nanocomposite for Dressing Materials

“…Bacterial cells were challenged for 24 h at 37 • C with shaking (160 rpm). The effect of films and Exf -GO on bacterial growth was evaluated through the spot plate count method [37], incubating an aliquot of challenged bacterial suspensions on LB agar recovery plates at 37 • C for 24 h, and comparing the number of colony forming units (CFU) to those obtained in the case of an unchallenged culture. The data are expressed as the average of the logarithm of the CFU per milliliter of culture (Log 10 CFU mL −1 ) for each biological trial (n = 3) with standard deviation.…”

Tunable photoluminescence properties of selenium nanoparticles: biogenic versus chemogenic synthesis

“…Among the broad spectrum of metal(loid) ionic species used as precursors for biogenic nanomaterial (NM) synthesis, those containing selenium (Se)i.e., selenite (SeO 3 2− ) and selenate (SeO 4 2− )have gained particular interest, as they can be very toxic at relatively low concentrations, because of their mobility through the trophic chain and their tendency to bioaccumulate. In the past, bacteria have been used to remediate environmental matrices contaminated with Se compounds, attenuating their critical concentration and, simultaneously, producing selenium NSs (SeNSs), which can be recovered [3][4][5][6][7]. This aspect represents a technological advantage since Se is a scarce and rare element of our Earth's crust featuring properties (e.g., high photoconductivity, piezoelectricity, thermoelectricity, spectral sensitivity) [8][9] that makes it of utmost importance at an economic level.…”

“…For instance, optical and photoluminescence (PL) properties of these metal NMs [14] can be exploited for the generation of sound and innovative nanosensors and imaging markers, avoiding the need for additional fluorescent tags (proteins or dyes), which often leads to observational artifacts [15]. On this matter, metal or metal-based NSs have been studied in depth for their optical and PL features, yet this knowledge in the case of SeNSs is still lagging [6,[16][17]. Indeed, only few research groups started in the last 4 years to focus on the possibility to use chemogenic SeNSs for eukaryotic cell imaging, exploiting the ability of Se nanoproducts to emit light beyond the so-called biological window (300-500 nm), where cellular components (e.g., collagens and flavins) fluoresce, causing interference with most of the organic fluorescent compounds or Quantum Dots (QDs) [15][16].…”

“…To date, biogenic SeNMs were investigated for their applications in (i) biomedicine, as antimicrobial [19][20][21][22][23][24][25][26][27], anticancer [27][28][29][30][31][32][33][34][35][36][37][38] and antioxidant [27,[39][40][41] agents, due to their high biocompatibility towards eukaryotic in vitro and in vivo systems [22,28,40,42], (ii) photocatalysis, and (iii) biosensing or pollutant adsorption [43][44][45][46], leaving still unveiled the potentiality of these NSs as a bioimaging tool. In particular, the PL properties of SeNPs produced by bacteria just recently began to be explored, as in the case of those recovered from the environmental isolate Stenotrophomonas maltophilia SeITE02 under metabolically controlled growth conditions [6]. Herein, the dependency of optical and PL properties on the size and shape of SeNPs synthesized by SeITE02 cells when grown in diverse complex media was studied, making a parallel with chemogenic SeNPs.…”

Towards a new treatment against polymicrobial infections: high antibacterial activity of lemon IntegroPectin againstPseudomonas aeruginosaandEscherichia coli

“…[33] The kill curve reporting the number of viable CFU mL -1 as a function of the concentration of both pectins is expressed in logarithmic (Log10) scale with standard deviation (n = 3), as described elsewhere. [34] Experiments with E. coli A single colony was inoculated into LB medium and incubated at 37°C overnight (o.n.). An aliquot (5 µL) of the o.n.…”