DEVELOPMENT OF EUROPIUM-LABELED ESCHERICHIA COLI AS A BACTERIAL TRACER FOR WATER QUALITY STUDIES

Escherichia coli (E.coli) has been used as an indicator microorganism in water quality studies to detect the presence of pathogenic microbes in the event of accidental or intentional release of these bacteria to the environment. In the development of bacterial tracer, to differentiate the tracer E.coli from background fecal coliform, the bacteria were tagged with europium (Eu), a lanthanide series rare earth metal. A high voltage electroporation technique was employed to introduce the Eu into the bacteria. The Eu tag was prepared by dissolving Eu (III) chloride salts in MilliQ water at a final concentration of 1.84 mg/L. A total of 0.02-g dry weight of E.coli cells were mixed with the 100-mL of Eu (III) chloride salt solution and the mixture was chilled at 2^oC for at least 3 hours before electroporation. The electroporator (BioRad Gene Pulser^TM) was preset at the default capacitance and resistance of 25mF and 200W, respectively. Then the chilled cell suspension was transferred into the electroporation chamber. After the shock treatment, the cells were suspended in Luria Broth culture media at 37^oC for at least 2 hours. Eu absorbed by the cells was analyzed using Instrumental Neutron Activation Analysis (INAA). INAA was chosen because (a) more than one element can be analyzed simultaneously, thus allowing for multiple tags, (b) no special preparations were needed except for filtering and drying the samples, and (c) samples can be stored for a long period prior to analysis. The effectiveness of the electroporation method was obtained by comparing the mass loading of Eu with the mass of Eu incorporated into non-electroporated cells cultured with the Eu solution. It was found that the electroporation increased Eu absorption by 3.6 fold. A final Eu to cell mass ratio of 0.021-g per g of dried cells was obtained. Electroporation coupled with INAA has the significant potential to be an effective technique for preparing and quantifying Eu-labeled E.coli as an environmental bacterial tracer.