ADSORPTION ONTO NATURAL CONSORTIA OF BACTERIA: A TEST OF THE UNIVERSALITY OF BACTERIAL SURFACE ADSORPTION

The adsorption of metal onto bacterial surfaces can control the mobility and speciation of metals in a wide range of environments. Previous research on pure strains of bacteria has noted that a range of bacteria adsorb metals to similar extents, suggesting a universality of adsorption behavior. In this study, we test this universality by determining: (1) whether consortia of bacteria in nature adsorb metals to similar extents and (2) whether natural consortia adsorb metals to the same extent as individual species. We cultured bacterial consortia from a variety of environments, including a forest, a river, a natural wetland, a wastewater treatment facility, a coal pile, and a former manufactured gas plant (MGP) site. Diversity of the consortia was quantified using denaturing gradient gel electrophoresis (DGGE). Potentiometric titration and Cd adsorption experiments were conducted using the bacterial consortia, and the results were modeled to solve for proton and Cd binding constants. DGGE results reveal that the consortia were diverse, averaging more than four species of bacteria from each sample. The calculated acidity constants and site concentration values for the surface functional groups were similar for all of the ‘natural’ consortia (forest, river, wetland, and treatment facility), but were significantly different for the ‘extreme’ consortia (coal and MGP site). The metal adsorption experiments indicated that the ‘natural’ bacterial consortia adsorbed Cd to similar extents, while the ‘extreme’ consortia adsorbed significantly more Cd. Previously studied individual bacteria species adsorbed Cd to greater extents than the ‘natural’ consortia. These results suggest that bacteria-metal adsorption in most natural environments can be described using a surface complexation approach with the ‘universal’ thermodynamic parameters developed here. Models that rely on individually cultivated species likely over-predict the amount of bacteria-metal adsorption in nature.