Effect of Tris-HCl Buffer on DNA Adsorption by a Variety of Soil Constituents

We investigated the effect of tris(hydroxymethyl) aminomethane hydrochloride (Tris-HCl) buffer (pH 7.0) as a bulk solution on the adsorption of DNA by gibbsite, goethite, montmorillonite, kaolinite, synthetic and natural allophanes, two humic acids and two andosols. The natural allophane, gibbsite, kaolinite and an andosol adsorbed significantly more DNA in a 0.1 M Tris-HCl buffer than in a 0.1 M NaCl solution (t-test, P < 0.005). In contrast, montmorillonite adsorbed significantly less DNA in the Tris-HCl than NaCl solution (P < 0.05). Care should be taken when using Tris-HCl in studies on the adsorption of extracellular DNA molecules by soil particles.