Abstract

Background: Cadmium Telluride (CdTe) Quantum Dots have several applications in different fields of industry because of their optic and electronic properties. Synthesis of these structures had been successfully performed by chemical methods. However, the procedures and mechanisms underlying microbiological synthesis of CdTe have not yet been clearly established. One of the main handicaps for these purposes is the elevated toxicity of the most soluble tellurium form, tellurite (TeO32), whose MIC is as low as 0.004 M for Escherichia coli. Given the growing interest in nanostructure formation through biological processes is that tellurite resistant bacteria represent an interesting source for biosynthesizing  CdTe Quantum Dots. There are several bacterial strategies for tellurite resistance and one of them is its reduction to the elemental form (Te0) often through the formation of black deposits. In this line, tellurite-treated bacteria would need two additional electrons for CdTe formation (Te2-); these could be provided in mineral oil-overlayed media, which would avoid volatile sulfide release and potentially increase the concentration of cellular thiol groups. Methods: Selected tellurite resistant strains were treated with potassium tellurite (K2TeO3) and cadmium chloride (CdCl2) and their reduction abilities and CdTe formation were compared to those of the tellurite-sensitive bacterium Escherichia coli BW25113 under aerobic, mineral oil coated-cultures and anaerobic conditions. CdTe quantum dots were detected by fluorescence. Results: It was observed that tellurite resistant bacteria treated with potassium tellurite and cadmium chloride were able to reduce tellurite to its elemental form in the presence and absence of oxygen, exhibiting the typical  blackening of cells because the formation of  elemental tellurium. In mineral oil covered culture media, the same strains reduced tellurite to telluride and formed CdTe, which were observed by the intrinsic fluorescence of quantum dots. E. coli did not form CdTe quantum dots in the tested conditions. Conclusion: In mineral oil covered cultures, the greater reduction potential of tellurite resistant bacteria represents a good source for the biological synthesis of tellurium nanocomposites.