Study of Thermokinetic Properties of Sodium Selenite on Bacillus thuringiensis Cry B by Microcalorimetry

By using an LKB2277 Bioactivity Monitor, the power‐time curves of Bacillus thuringiensis Cry B at 28°C effected by Na₂SeO₃ were determined. Some parameters, such as growth rate constants k, inhibitory ratio I, the maximum beat production rate P_max, heat output Q, were obtained. Considering both the growth rate constant k and heat output Q, we found that a low concentration of Na₂SeO₃ had a promoting action on the growth of Bacillus thuringiensis Cry B, but a high concentration of Na₂SeO₃ had an inhibitory action. The toxicity of a toxicant can also be expressed as half inhibitory concentration IC₅₀ of toxicant, i. e., 50% effective in this inhibition. The value of IC₅₀ of Na₂SeO₃on Bacillus thuringiensis Cry B is 117 μg/mL. This microcalorimetric bioassay for cellular toxicity is based on metabolic heat evolution from cultured cells. The assay is quantitative, inexpensive, and versatile.