Browsing by Author "Piacenza, Elena"

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    Bacterial Production of Selenium and Tellurium Nanostructures and their Biophysical-Chemical Characterization
    (2019-04-29) Piacenza, Elena; Turner, Raymond Joseph; Prenner, Elmar J.; Anikovskiy, Max; Trudel, Simon; Lenz, Markus
    The demand for green and “low carbon” technologies has led to the exploitation of various metal or metalloid – metal(loid) – elements in various applications, among which renewable energy production is one of the most pressing. This tendency is resulting in a rapid accumulation of metal(loid) compounds in the environment, posing the emergency of the decontamination of polluted areas. Since most of the metal(loid)s of high technological and economic interest are scarcely present on our Earth’s crust, their recent increased use has also underlined the need of their reclamation to avoid their depletion. Selenium and tellurium are considered to date “energy-critical elements”, as they are of paramount importance to produce sustainable energy and to advance in the technological and biomedical fields. In view of the need to reclaim metalloids from different environmental matrices, the ability of several microorganisms to bioprocess selenium or tellurium compounds into their less bioavailable elemental states producing metalloid based nanomaterials acquires a double importance in terms of bioremediation strategy and technological relevance. This PhD project presents a deep study regarding the exploration of three different bacterial strains, i.e., Rhodococcus aetherivorans BCP1, Ochrobactrum sp. MPV1 and Stenotrophomonas maltophilia SeITE02, as cell factories for the biosynthesis of selenium or tellurium nanostructures. Key parameters influencing fundamental features of the material at the nanoscale, such as size and morphology, and their recovery (e.g., localization with respect to the bacterial cells) are analyzed in this thesis to lay the groundwork for the optimization of metalloid nanomaterial biosynthesis and the development of ad hoc strategies for their recovery from bacterial cultures. Moreover, the bioprocess strategies used by Ochrobactrum sp. MPV1 and S. maltophilia SeITE02 to cope with selenium toxicity are here explored to shed light into the mechanisms used by different microorganisms to thrive under metalloid pressure. The obtained biogenic selenium or tellurium nanostructures were then physically-chemically characterized, bringing to light (i) the structural similarities between chemogenic and biogenic nanomaterials, (ii) the unique feature of an organic material acting as stabilizing agent of the nanostructures, as well as (iii) their photoluminescence and electrical properties, which can be exploited for their future applications.
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    Ochrobactrum sp. MPV1 from a dump of roasted pyrites can be exploited as bacterial catalyst for the biogenesis of selenium and tellurium nanoparticles
    (2017-11-28) Zonaro, Emanuele; Piacenza, Elena; Presentato, Alessandro; Monti, Francesca; Dell’Anna, Rossana; Lampis, Silvia; Vallini, Giovanni
    Abstract Background Bacteria have developed different mechanisms for the transformation of metalloid oxyanions to non-toxic chemical forms. A number of bacterial isolates so far obtained in axenic culture has shown the ability to bioreduce selenite and tellurite to the elemental state in different conditions along with the formation of nanoparticles—both inside and outside the cells—characterized by a variety of morphological features. This reductive process can be considered of major importance for two reasons: firstly, toxic and soluble (i.e. bioavailable) compounds such as selenite and tellurite are converted to a less toxic chemical forms (i.e. zero valent state); secondly, chalcogen nanoparticles have attracted great interest due to their photoelectric and semiconducting properties. In addition, their exploitation as antimicrobial agents is currently becoming an area of intensive research in medical sciences. Results In the present study, the bacterial strain Ochrobactrum sp. MPV1, isolated from a dump of roasted arsenopyrites as residues of a formerly sulfuric acid production near Scarlino (Tuscany, Italy) was analyzed for its capability of efficaciously bioreducing the chalcogen oxyanions selenite (SeO3 2−) and tellurite (TeO3 2−) to their respective elemental forms (Se0 and Te0) in aerobic conditions, with generation of Se- and Te-nanoparticles (Se- and TeNPs). The isolate could bioconvert 2 mM SeO3 2− and 0.5 mM TeO3 2− to the corresponding Se0 and Te0 in 48 and 120 h, respectively. The intracellular accumulation of nanomaterials was demonstrated through electron microscopy. Moreover, several analyses were performed to shed light on the mechanisms involved in SeO3 2− and TeO3 2− bioreduction to their elemental states. Results obtained suggested that these oxyanions are bioconverted through two different mechanisms in Ochrobactrum sp. MPV1. Glutathione (GSH) seemed to play a key role in SeO3 2− bioreduction, while TeO3 2− bioconversion could be ascribed to the catalytic activity of intracellular NADH-dependent oxidoreductases. The organic coating surrounding biogenic Se- and TeNPs was also characterized through Fourier-transform infrared spectroscopy. This analysis revealed interesting differences among the NPs produced by Ochrobactrum sp. MPV1 and suggested a possible different role of phospholipids and proteins in both biosynthesis and stabilization of such chalcogen-NPs. Conclusions In conclusion, Ochrobactrum sp. MPV1 has demonstrated to be an ideal candidate for the bioconversion of toxic oxyanions such as selenite and tellurite to their respective elemental forms, producing intracellular Se- and TeNPs possibly exploitable in biomedical and industrial applications.