The purpose of this research was: (1) to determine the bacterial toxicity of the selenocyanate anion by determining minimal inhibitory and bactericidal concentrations and to determine how much selenium and tellurium three different types of bacteria could incorporate into their cells when exposed to sodium selenite and potassium tellurite; and (2) to determine the ratios of cadmium and tellurium present in cadmium telluride nanoparticles by using ICP-AES.
Minimal inhibitory and minimal bactericidal concentrations (MIC and MBC respectively) were determined for three different bacteria by using a 96-microwell plate. A blue color indicated that those bacteria contained no metabolic activity; a pink color indicated that bacteria were functioning metabolically. The smallest concentration to retain its blue color was designated the MIC. Wells surrounding the MIC were plated onto LB agar plates and left to incubate overnight. The MBC was determined to be the plated concentration that contained no growth of bacteria. For bacterial consumption experiments, each strain of bacteria was left to incubate at certain time intervals with a specific concentration of metalloidal salt. Samples were centrifuged and pellets were taken to dryness and resuspended in dilute nitric acid. The samples were then analyzed via ICP-AES. Cadmium telluride NPs were biosynthesized and synthesized according to methods developed by collaborators at the University of Chile and University of Santiago. Upon being biosynthesized or synthesized, nanoparticle fluorescence was observed by using a UV trans illuminator. The samples were analyzed via ICP-AES.
The toxicity experiments showed that selenocyanate had 1) an MIC of 400 mM for LHVE, 250 mM for the wild-type E. coli species, and 125 mM for TM1b, and 2) an MBC of 450 mM for LHVE, 300 mM for the wild-type E. coli species, and 200 mM for TM1b. Through these experiments, to our knowledge, the first evidence for the biological production of elemental Se by a metalloid-resistant bacterium amended with selenocyanate was discovered. Consumption experiments showed the incorporation of selenium and tellurium oxyanions by all three types of bacteria. Analysis by ICP-AES demonstrated that LHVE more successfully incorporates Te and Se into cells as compared to E. coli or TM1B. The nanoparticle synthesis and biosynthesis experiments showed that fluorescent cadmium telluride nanoparticles were successfully produced both biologically and chemically. The ratios of cadmium and tellurium in these nanoparticles were determined.
Keywords: metalloid-resistant bacteria, minimum inhibitory, minimum bactericidal concentrations, glutathione, fluorescence