Distinct Effects of Chemical Toxicity and Radioactivity on Metabolic Heat of Cultured Cells Revealed by Isotope-Editing

Studying the toxicity of chemical compounds using isothermal microcalorimetry (IMC), which monitors the metabolic heat from living microorganisms, is a rapidly expanding field. The unprecedented sensitivity of IMC is particularly attractive for studies at low levels of stressors, where lethality-based data are inadequate. We have revealed via IMC the effect of low dose rates from radioactive beta(-)-decay on bacterial metabolism. The low dose rate regime (<400 mu Gyh(-1)) is typical of radioactively contaminated environmental sites, where chemical toxicity and radioactivity-mediated effects coexist without a predominance or specific characteristic of either of them. We found that IMC allows distinguishing the two sources of metabolic interference on the basis of isotope-editing and advanced thermogram analyses. The stable and radioactive europium isotopes Eu-153 and Eu-152, respectively, were employed in monitoring Lactococcus lactis cultures via IMC. beta(-)-emission (electrons) was found to increase initial culture growth by increased nutrient uptake efficiency, which compensates for a reduced maximal cell division rate. Direct adsorption of the radionuclide to the biomass, revealed by mass spectrometry, is critical for both the initial stress response and the dilution of radioactivity-mediated damage at later culture stages, which are dominated by the chemical toxicity of Eu.

Automated summary

The study of chemical compound toxicity using isothermal microcalorimetry (IMC) is a rapidly growing field that utilizes the metabolic heat from living microorganisms. By using IMC, we have discovered the effect of low dose rates of radioactive beta(-)-decay on bacterial metabolism. The sensitivity of IMC allows for the distinction between the metabolic interferences caused by radioactivity and chemical toxicity, providing valuable insights into contaminated environmental sites.