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Equilibrium adsorption and binding of DNA from Bacillus subtilis on humic acids (HA) extracted from a forest soil, the capacity of the bound DNA to transform B. subtilis, and the resistance of the bound DNA to degradation by DNase I are reported. Adsorption of DNA on the HA was maximal after 2 and 4 h at pH 3.0 and 4.0, respectively. The adsorption of a constant amount of DNA (50 μg) on increasing concentrations of the HA reached a plateau with 2 and 3 mg of HA at pH 3.0 and 4.0, respectively. No plateau was observed when increasing amounts of DNA where adsorbed on a constant amount of the HA (2 mg). 70 to 80% of the adsorbed DNA was tightly bound after two washes with 0.1 M NaCl (pH 6.4), double distilled water (pH 5.5), or DNA buffer (pH 4.0). Bound DNA was capable of transforming auxotrophic and chloramphenicol-sensitive cells of B. subtilis, although at a lower frequency than free DNA. DNA bound on the HA was protected more against degradation by DNase I than free DNA: the concentration of DNase required to inhibit transformation by bound DNA was approximately 100 times higher than that required to inhibit transformation by comparable amounts of free DNA.
Crecchio et al. (Sat,) studied this question.