Adsorption and binding of dirty DNA on Ca homoionic montmorillonite and kaolinite

Bacterial transformation of pure DNA adsorbed by soil particles can occur in the presence of a competent cell and the adsorbed nucleic acid is protected from DNase degradation. However, the release of impure rather than pure DNA is more common in the extracellular soil environment, especially considering that microbial death and lysis is a common event in soil. Thus, there is the need to study the adsorption of dirty (impure) DNA by soil particles. The adsorption isotherm onto montmorillonite or kaolinite, homoionic to Ca2+, showed that the amount of pure DNA adsorbed and bound by both clay minerals was higher than that of dirty DNA. Dirty DNA adsorbed onto clay minerals, especially in the presence of cellular debris, was easily desorbed by washing with double distilled water respect to the pure DNA. Clay minerals protected both pure and dirty DNA from the DNaseI activity; also cellular debris protected dirty DNA from DNase activity, but the length of the DNA fragments was lower respect to that observed in the presence of clay minerals.