Development of an Accurate Toxicity Assay Using Genetically Engineered Bioluminescent Bacteria

Methods of developing and improving toxicity assays using genetically engineered bioluminescent bacteria PM6 and Shk1 were investigated. The EC₅₀ values for three metals (zinc, copper, and lead) were determined using these two strains and were compared with the EC₅₀ values calculated from the Microtox® assay, published inhibition to activated sludge specific oxygen uptake rate (SOUR) data (Madonii et al., 1999), and published EC₅₀ values from Microtox® for the same compounds (Kaiser and Devillers, 1994). This was done to evaluate the effectiveness of using strains PM6 and Shk1 to predict toxic effects to activated sludge as indicated by respiration inhibition. A number of factors affecting toxicity assays were examined including temperature control, cell storage method (lyophilization and storage temperature), activation time, and mixing prior to luminescence measurement.

A toxicity testing protocol developed by Lajoie et al. (2002) was used and adapted to this study. Based on the results of these experiments, it was concluded that toxicity assays using PM6 and Shk1 provide EC₅₀ values closer to respiration inhibition EC₅₀ values than Microtox®.