THE EFFECT OF IONIC-STRENGTH ON THE ADSORPTION OF H-SUBTILIS AND BACILLUS-LICHENIFORMIS - A SURFACE COMPLEXATION MODEL(, CD2+, PB2+, AND CU2+ BY BACILLUS)

To quantify metal adsorption onto bacterial surfaces, recent studies h ave applied surface complexation theory to model the specific chemical and electrostatic interactions occurring at the solution-cell wall in terface. However, to date, the effect of ionic strength on these inter actions has not been investigated. In this study, we perform acid-base titrations of suspensions containing Bacillus subtilis or Bacillus li cheniformis in 0.01 or 0.1 M NaNO3, and we evaluate the constant capac itance and basic Stern double-layer models for their ability to descri be ionic-strength-dependent behavior, The constant capacitance model p rovides the best description of the experimental data. The constant ca pacitance model parameters vary between independently grown bacterial cultures, possibly due to cell wall variation arising from genetic exc hange during reproduction. We perform metal-B. subtilis and metal-B. l icheniformis adsorption experiments using Cd, Pb, and Cu, and we solve for stability constants describing metal adsorption onto distinct fun ctional groups on the bacterial cell walls. We find that these stabili ty constants vary substantially but systematically between the two bac terial species at the two different ionic strengths. (C) 1998 Academic Press.