Microcalorimetric study of the action of Ce(III) ions on the growth of E. coli.

A microcalorimetric technique based on bacterial heat output was used to evaluate the action of Ce(III) ions on the growth of Escherichia coli. The power-time curves of the growth metabolism of the bacteria were studied in the presence and absence of Ce(III) by means of a LKB-2277 Bioactivity Monitor, by a stopped-flow method at 37 degrees C. For evaluation of the results, the maximum power, Pmax, the growth rate constant k, and the heat effects Qlog, Qstat, and Qtot for the log phase, the stationary phase, and total heat output, respectively, were determined. For comparison, a spectrophotometer was used to estimate the number of cells in the liquid culture. The shape of the bacteria was examined by electron microscopy. We concluded that the presence of cerium ions at concentrations below 350 microg/mL have a stimulatory effect on the growth of E. coli, whereas concentrations at or above 400 microg/mL may have an inhibitory effect.