Clay-nucleic acid complexes: Characteristics and Implications for the preservation of genetic material in primeval habitats

The equilibrium adsorption of three nucleic acids: chromosomal DNA, superco iled plasmid DNA, and 25S rRNA, on the clay minerals, montmorillonite (M) a nd kaolinite (K), were studied. Adsorption of the nucleic acid on the clays was rapid and maximal after 90 min of contact time. Chromosomal DNA was ad sorbed to a greater extent than plasmid DNA and RNA, and the adsorption was also greater on M than on K. Adsorption isotherms were of the L type, and a plateau was reached with all the complexes, with the exception of chromos omal DNA adsorbed on M. To determine where nucleic acids are adsorbed on cl ay minerals and the nature of the interaction, complexes were studied by X- ray diffraction (X-RD), electron microscopy, and Fourier transform infrared (FT-IR) spectroscopy. X-RD showed that nucleic acids did not penetrate the clay, indicating that the adsorption occurred primarily on the external su rfaces of clay particles, as also suggested by electron microscopy observat ions. FT-IR spectra of clay-tightly bound nucleic acid complexes showed abs orption bands that indicate a variation of the nucleic acids status as a co nsequence of their adsorption on clay. Data obtained suggested that the for mation of clay-nucleic acid complex could have an important role in the pre servation of genetic material in primeval habitats.