Chromosomal DNA from Bacillus subtilis and different forms of plasmid pHV14 (covalently closed circular (CCC), linear monomer (M), and linear multimer (LM)) were adsorbed and bound on the clay mineral montmorillonite. After extensive washing of the clay‐DNA complexes with DNA buffer (pH 7.5), approx. 25% of the chromosomal DNA, and approx. 30, 90, and 5%, respectively, of the CCC, M and LM form remained bound. Chromosomal and plasmid DNA bound on clay were capable of transforming competent cells, with different specific activities. The clay‐DNA complexes persisted in non‐sterile soil and retained transforming ability up to 15 days after their addition to the soil. DNA bound on montmortillonite was protected from the activity of EcoRI, supporting the evidence that DNA adsorbed on soil components was resistant to degradation by nucleases.

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