A microcalorimetric method for studying the biological effects of La3+ on Escherichia coli

A microcalorimetric technique based on the bacterial heat-output was explor ed to evaluate the stimulatory effect of La3+ on Escherichia coli. The powe r-time curves of the growth metabolism of E. coli and the effect of La3+ on it were studied using an LKB-2277 BioActivity Monitor, stopped-flow method ; at 37 degreesC. For evaluation of the results, the maximum power (P-max), the growth rate constants (k) and the heat effects (Q(LOG), Q(STAT)) for t he log phase, the stationary phase and the total heat effect (Q(T)) for E. coli were determined. The microcalorimetric method agreed with the conventi onal methods, such as cell numbers and biomass. La3+ in the concentration r anges of 0-400 mug/ml has stimulatory effects on E. coli, while La3+ ion of higher concentrations (> 400 mug/ml) can inhibit the growth. This phenomen on is very similar to those observed from the in vitro cells and tissues fr om animals, plants and some microorganisms by other methods. (C) 2000 Elsev ier Science B.V. All rights reserved.