Examinando por Autor "Chasteen, Thomas G."

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    Enhanced Glutathione Content Allows the In Vivo Synthesis of Fluorescent CdTe Nanoparticles by Escherichia coli
    (Public Library of Science, 2012-11-21) Monrás, Juan P.; Díaz, Víctor; Bravo, Denisse; Montes, Rebecca A.; Chasteen, Thomas G.; Osorio-Román, Igor O.; Vásquez, Claudio C.; Pérez-Donoso, José M.
    The vast application of fluorescent semiconductor nanoparticles (NPs) or quantum dots (QDs) has prompted the development of new, cheap and safer methods that allow generating QDs with improved biocompatibility. In this context, green or biological QDs production represents a still unexplored area. This work reports the intracellular CdTe QDs biosynthesis in bacteria. Escherichia coli overexpressing the gshA gene, involved in glutathione (GSH) biosynthesis, was used to produce CdTe QDs. Cells exhibited higher reduced thiols, GSH and Cd/Te contents that allow generating fluorescent intracellular NP-like structures when exposed to CdCl2 and K2TeO3. Fluorescence microscopy revealed that QDs-producing cells accumulate defined structures of various colors, suggesting the production of differently-sized NPs. Purified fluorescent NPs exhibited structural and spectroscopic properties characteristic of CdTe QDs, as size and absorption/emission spectra. Elemental analysis confirmed that biosynthesized QDs were formed by Cd and Te with Cd/Te ratios expected for CdTe QDs. Finally, fluorescent properties of QDs-producing cells, such as color and intensity, were improved by temperature control and the use of reducing buffers. © 2012 Monrás et al.
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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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    Microarray analysis of the Escherichia coli response to CdTe-GSH Quantum Dots: Understanding the bacterial toxicity of semiconductor nanoparticles
    (BioMed Central Ltd., 2014) Monrás, Juan P.; Collao, Bernardo; Molina-Quiroz, Roberto C.; Pradenas, Gonzalo A.; Saona, Luis A.; Durán-Toro, Vicente; Órdenes-Aenishanslins, Nicolás; Venegas, Felipe A.; Loyola, David E.; Bravo, Denisse; Calderón, Paulina F.; Calderón, Iván L.; Vásquez, Claudio C.; Chasteen, Thomas G.; Lopez, Desiré A.; Pérez-Donoso, José M.
    Background: Most semiconductor nanoparticles used in biomedical applications are made of heavy metals and involve synthetic methods that require organic solvents and high temperatures. This issue makes the development of water-soluble nanoparticles with lower toxicity a major topic of interest. In a previous work our group described a biomimetic method for the aqueous synthesis of CdTe-GSH Quantum Dots (QDs) using biomolecules present in cells as reducing and stabilizing agents. This protocol produces nanoparticles with good fluorescent properties and less toxicity than those synthesized by regular chemical methods. Nevertheless, biomimetic CdTe-GSH nanoparticles still display some toxicity, so it is important to know in detail the effects of these semiconductor nanoparticles on cells, their levels of toxicity and the strategies that cells develop to overcome it. Results: In this work, the response of E. coli exposed to different sized-CdTe-GSH QDs synthesized by a biomimetic protocol was evaluated through transcriptomic, biochemical, microbiological and genetic approaches. It was determined that: i) red QDs (5 nm) display higher toxicity than green (3 nm), ii) QDs mainly induce expression of genes involved with Cd+2 stress (zntA and znuA) and tellurium does not contribute significantly to QDs-mediated toxicity since cells incorporate low levels of Te, iii) red QDs also induce genes related to oxidative stress response and membrane proteins, iv) Cd2+ release is higher in red QDs, and v) QDs render the cells more sensitive to polymyxin B. Conclusion: Based on the results obtained in this work, a general model of CdTe-GSH QDs toxicity in E. coli is proposed. Results indicate that bacterial toxicity of QDs is mainly associated with cadmium release, oxidative stress and loss of membrane integrity. The higher toxicity of red QDs is most probably due to higher cadmium content and release from the nanoparticle as compared to green QDs. Moreover, QDs-treated cells become more sensitive to polymyxin B making these biomimetic QDs candidates for adjuvant therapies against bacterial infections. © 2014 Monrás et al.