Examinando por Autor "Díaz-Vásquez, Waldo A."

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    Isolation, identification and characterization of highly tellurite-resistant, tellurite-reducing bacteria from Antarctica
    (Elsevier, 2014-03) Arenas, Felipe, A.; Pugin, Benoit; Henríquez, Nicole, A.; Arenas-Salinas, Mauricio, A.; Díaz-Vásquez, Waldo A.; Pozo, María F.; Muñoz, Claudia M.; Chasteen, Thomas G.; Pérez-Donoso, José M.; Vásquez, Claudio C.
    The tellurium oxyanion, tellurite, is extremely noxious to most living organisms. Its toxicity has been mainly related to the generation of reactive oxygen species (ROS) as well as to an unbalancing of the thiol:redox buffering system. Nevertheless, a few bacteria are capable of thriving at high tellurite concentrations. One mechanism of resistance is the enzymatic and non-enzymatic reduction of tellurite to the less toxic elemental tellurium. This reduction generates nano- to micrometric tellurium crystals that display different shapes and sizes.To date, a very limited number of highly tellurite-resistant and tellurite-reducing bacterial species are available from international culture collections. In this work, we decided to look for tellurite-reducing bacteria from an extreme environment, Antarctica. This environment exhibits a combination of several extreme factors such as high UV-radiation and desiccation and freezing conditions that impact directly on the local biodiversity. Since, as does, all these factors induce ROS formation, we hypothesized that Antarctic bacteria could also exhibit tellurite-resistance. In this context, we isolated 123 tellurite-resistant bacteria, and characterized six new tellurite-resistant and tellurite-reducing bacterial strains from samples collected in Antarctica. These strains were identified according to their 16S rRNA gene sequence as Staphylococcus hameolyticus, Staphylococcus sciuri, Acinetobacter haemolyticus, Pseudomonas lini, and two strains of Psychrobacter immobilis.The isolates display tellurite-resistance about 35- to 500-fold higher than Escherichia coli (Te-sensitive organism), and a high level of tellurite reduction which might be interesting for an application in the field of bioremediation or nanoparticle biosynthesis. © 2014 Elsevier B.V. and NIPR.
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    Thermal and photo stability of glutathione-capped cadmium telluride quantum dots
    (Wichtig Publishing Srl, 2015) Wansapura, Poorna T.; Díaz-Vásquez, Waldo A.; Vásquez, Claudio C.; Pérez-Donoso, José M.
    Background: Nanoparticles (NPs) are increasingly being used in a number of applications that include biomedicine, biological labeling and cancer marker targeting, and their successful storage is important to preserve their viability. A systematic investigation of the thermal and photo stability of chemically stabilized cadmium telluride (CdTe) quantum dots (QDs) under various storage conditions either in solution or as dried nanoparticles has not been published. Here we report experiments involving chemically synthesized glutathione-capped CdTe QDs whose photoluminescence spectra were examined initially and then periodically during storage times up to 76 days. Methods: Samples of dried QDs or QDs in solution (water or buffered) were examined under different light conditions including complete darkness, constant 12,000 lux incident light, and under diurnal sunlight; at temperatures ranging from -80°C to room temperature. Results: Though QDs stored in solution in the dark at -80°C lost only 50% of peak fluorescence (FL510) within 2 weeks, solution-stored QDs exposed to sunlight at room temperature showed FL510 drops of 85% in the first 24 hours. In contrast, QDs precipitated from aqueous solution, dried and stored in time course experiments in the presence of atmospheric oxygen – when resuspended in water – lost an average of only 12% FL510 over 76 days under all conditions tested, even in direct sunlight. Conclusions: Glutathione-capped CdTe particles can be stored as dried nanoparticles for extended periods of time, enhancing their viability in biomedicine, biological labeling and cancer marker targeting. © 2015 Wichtig Publishing.