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    Comparison of Techniques for Evaluating the Effect of Cadmium on Pseudomas Fluorescens

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    Three techniques were compared in a study of the effect of cadmium on an aquatic strain of Pseudomonas fluorescens. The methods used were (1) direct microscopic counts using epifluorescence and formazan detection, (2) determination of colonyforming units, and (3) determination of intracellular adenosine triphosphate (ATP) using a firefly luciferase bioluminescent assay. Results of the plate count and ATP determinations demonstrated that P. fluorescens was stressed after exposure to 10-, 25-, 50-, and 100-ppm cadmium. The organisms recovered following treatment; however, only the ATP bioassay data indicated that there might be bacterial recovery at 12 h after the addition of 100-ppm cadmium. The acridine orange 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chlorine (INT) formazan reduction technique did not produce results that could be readily interpreted. The bacteria tended to clump together, and cells that had been exposed to 100-ppm cadmium generally did not fluoresce. In addition, it was not possible to detect formazan deposits in any of the cadmium-treated cells. Compared to the plate count procedure and the acridine orange INT-formazan reduction technique, the intracellular ATP assay appeared to be a more accurate method of determining the viability of P. fluorescens cells following cadmium treatment.


    toxicology, cadmium, Pseudomonas fluorescens, acridine orange INT-formazan reduction, plate counts, adenosine triphosphate (ATP) bioassay, hazard assessment, aquatic toxicology

    Author Information:

    Seyfried, PL
    Professor and graduate student, University of Toronto, Ontario, Canada

    Horgan, CBL
    Professor and graduate student, University of Toronto, Ontario, Canada

    Committee/Subcommittee: E47.01

    DOI: 10.1520/STP33582S