Cd adsorption onto bacterial surfaces: A universal adsorption edge?

In this study, we measure the thermodynamic stability constants for proton and Cd binding onto the Gram-negative bacteria Escherichia coli Pseudomonas aeruginosa, and the Gram-positive bacteria Bacillus megaturium, Streptococcus faecalis. Staphylococcus aureus, Sporosarcina ureae, and Bacillus cereus. Potentiometric titrations and Cd-bacteria adsorption experiments yield average values for the carboxyl site pK(a), site concentration, and log stability constant for the bacterial surface Cd-carboxyl complex of 5.0, 2.0 x 10(-3) mol/g and 4.0 respectively. Our results indicate that a wide range of bacterial species exhibit nearly identical Cd adsorption behavior as a function of pH. We propose that metal-bacteria adsorption is not dependent on the bacterial species involved, and we develop a generalized adsorption model which may greatly simplify the task of quantifying the effects of bacterial adsorption on dissolved mass transport in realistic geologic systems. Copyright (C) 2001 Elsevier Science Ltd.