Thanh H. (Helen) Nguyen, Deepartment of Chemical Engineering, Environmental Engineering Program, Yale University, P.O.Box 208286, New Haven, CT 06520-8286 and Menachem Elimelech, Department of Chemical Engineering, Environmental Engineering Program, Yale University, P.O.Box 208286, New Haven, CT 06520-8286.
Extracellular DNA has been shown to survive enzymatic degradation and subsequently to transform competent microorganisms. Factors contributing to the transport and fate of extracellular DNA in subsurface environments include adhesion rate, adhesion reversibility, and conformation of the adhered DNA onto mineral surfaces. In addition, solution chemistry and presence of natural organic matter (NOM) on mineral surfaces are expected to play an important role. In this study, a quartz crystal microbalance with dissipation (QCM-D) has been used to determine the adhesion rate of plasmid DNA onto a silica surface coated with NOM. The structure of the resulting adsorbed DNA layer was elucidated by analyzing the viscoelastic properties of the adsorbed DNA layers formed and exposed to solutions with different ionic composition. To better understand the DNA adhesion mechanisms and physicochemical properties of the adhered layer, the QCM-D data are complemented by dynamic light scattering measurements of diffusion coefficients of the DNA molecules as a function of solution ionic composition. Results based on our model system suggest that adhesion of DNA molecules to NOM-coated mineral surfaces is possible and stable, especially in the presence of divalent cations such as Ca2+ and Mg2+, or at moderately high Na+ concentrations. In addition, a sudden decrease in solution ionic strength, such as the case during a rain event, is not likely to release adhered DNA from mineral surfaces coated with NOM.