Role of bacteria in the adsorption and binding of DNA on soil colloids and minerals.

Adsorption and desorption of salmon sperm DNA on bacteria (Bacillus thuringiensis, Pseudomonas putida), two different colloidal fractions (organic and inorganic clay) from an Alfisol, minerals (montmorillonite, kaolinite and goethite) and colloid-bacteria composites were studied. Similar adsorption capacity and affinity of DNA were observed on two bacterial cells. However, the two bacterial strains played different roles in affecting the adsorption of DNA on the composites of soil colloidal particles with bacteria. The introduction of B. thuringiensis in soil colloids and minerals systems dramatically promoted DNA adsorption on colloidal particles especially organic clay, while P. putida decreased the adsorption of DNA on kaolinite and goethite. Electrostatic force and ligand exchange are regarded to be the major driving forces involved in the adsorption of DNA on bacterial cells, montmorillonite, soil colloids and goethite. Presence of bacteria enhanced the proportion of DNA adsorption on soil colloidal particles by electrostatic force and depressed that by ligand exchange process. Information obtained in this study is of fundamental significance for the understanding of the ultimate fate of extracellular DNA in soil systems.