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Soil Biology & Biochemistry

Binding of DNA from Bacillus subtilis on Montmorillonite–Humic Acids–Aluminum or Iron Hydroxypolymers

Effects on Transformation and Protection against DNase

^a Dipartimento di Biologia e Chimica Agroforestale ed Ambietale, Univ. di Bari, Via Amendola 165/A, 70126 Bari, Italy
^b Dipartimento di Scienze Animali, Vegetali, e dell'Ambiente, Univ. del Molise, Via De Sancits s/n, 86100 Campobasso, Italy
^c Lab. of Microbial Ecology, Dep. of Biology, New York Univ., 100 Washington Sq. East, New York, NY 10003, USA

^* Corresponding author (crecchio{at}agr.uniba.it)

The equilibrium adsorption and binding of DNA from Bacillus subtilis on complexes of montmorillonite–humic acids Al or Fe hydroxypolymers (Al–M–HA or Fe–M–HA) at different M/HA ratios, the desorption of DNA, the capacity of bound DNA to transform competent cells of B. subtilis in vitro, and the protection of bound DNA from degradation by free and organomineral-bound DNase I are reported. Adsorption was rapid (maximal after 2 h), occurred from pH 3 to 10, and was higher on Al–M–HA than on Fe–M–HA. Saturation of the sites on the surface or between the layers of Al– or Fe–M–HA occurred with only some complexes, depending on how the complexes were prepared. Essentially no desorption under stringent conditions was observed. Bound DNA transformed auxotrophic competent cells of B. subtilis, although at a lower frequency than free DNA. Bound DNA was protected more than free DNA against degradation by DNase I, and differences in resistance to degradation between free and bound DNA were more evident when DNase was also bound on the organomineral complexes.

Abbreviations: Al–M–HA, montmorillonite–humic acids–Al hydroxypolymers • CEC, cation-exchange capacity • Fe–M–HA, montmorillonite–humic acids–Fe hydroxypolymers • HA, humic acid • HGT, horizontal gene transfer • M, montmorillonite • SSA, specific surface area • TBAB, tryptose blood agar base • XRD, x-ray powder diffractogram