CD, PB, AND CA ADSORPTION ONTO BACTERIAL SURFACES AT HIGH AND LOW TEMPERATURES

 

Bacteria are present in a range of both high and low temperature environments, yet little is known concerning the affect of temperature on the adsorption of aqueous metal cations onto bacterial surfaces.  In this study, we investigate the temperature dependence of metal adsorption onto bacteria by measuring pH-adsorption edges for Cd, Pb, and Ca onto the gram-positive species B. subtilis and onto the gram-negative species P. mendocina at 5, 50, and 80°C.  We conducted batch adsorption experiments at each temperature as a function of pH, exposing a bacterial solution to a metal-bearing 0.1 M NaClO₄ electrolyte solution for two hours and maintaining the desired temperature using a thermostated water bath.  The pH of each sample was measured at the temperature of each experiment with a potentiometer that was calibrated with buffers maintained at the temperature of interest.  After final pH determination, we filtered out the bacteria and used ICP-OES measurements to determine the concentration of metal left in solution.  All adsorption edge experiments were performed twice to test for reproducibility.

The experimental measurements indicate that the temperature dependence for Cd, Pb, and Ca adsorption onto bacterial surfaces is negligible.  The results imply that the stability constants of surface complexes do not change significantly over the temperature range of this study.  Similarly, Wightman et al. (2002) observed no significant temperature effect for bacterial surface protonation reactions from 30 to 75°C.  These observations could simplify modeling the effects of bacterial adsorption on mass transport because a single set of thermodynamic properties could describe the stabilities of bacterial surface complexes over a wide range of temperatures.