Ironing Out Genes in the Environment: An Experimental Study of the DNA-Goethite Interface

DNA fate in soil plays an important role in the cycling of genetic information in the environment. Adsorption onto mineral surfaces has great impact on this function. This study probes the kinetics, equilibrium behavior and bonding mechanisms associated with adsorption of DNA onto goethite, a common soil mineral. Surface sensitive ATR-FTIR and XPS approaches are applied to directly characterize the DNA-goethite interface. Adsorption kinetics follow a pseudo-first order model, suggesting adsorption rate is surface limited. Adsorption rate constants increase with DNA concentration, ranging from 3.29 X 10(-3) to 3.55 X 10(-4) min(-1). Equilibrium adsorption, as monitored by ATR-FTIR and XPS, follows the Langmuir model, with a high affinity of DNA for goethite observed (K = 1.25 x 10(3) and 9.48 x 10(2) mL/mg for ATR-FTIR and XPS, respectively). ATR-FTIR and XPS characterization of the structure of surface adsorbed DNA demonstrates inner-sphere coordination between backbone phosphate groups of DNA and goethite. Furthermore, adsorbed DNA retains a B-form, suggesting the DNA helix adsorbs on goethite without degradation or alteration to helical structure, despite binding of backbone phosphate groups. This work advances our understanding of the environmental behavior of DNA by characterizing the mechanism of adsorption onto a prominent soil mineral.