Effect of food processing on the fate of DNA with regard to degradation and transformation capability in Bacillus subtilis

Soymilk, tofu, corn masa, and cooked potato were produced from transgenic raw materials and the effect of processing on the degradation of DNA was studied. Major degrading factors were for soymilk and tofu the mechanical treatment of soaked soybeans and for corn masa and cooked potatoes the thermal treatment. In the processed foods no DNA fragments > 1.1 kb were detected. We included in our studies the effect of the size of donor DNA and length of the homologous sequence on the marker rescue transformation of B. subtilis LTH 5466, which was monitored by restoration of deleted nptII. When DNA fragments (168, 414, 658, and 792 bp) of nptII and linearized plasmid DNA (pGEM-T-1, 3168 by and pGEM-T-2, 3792 6p) containing the 168 by or 792 by fragments, respectively, were used as donor DNA, it was observed that the efficiency of marker rescue decreased with decreasing length of homologous sequence. The use of a larger plasmid (pMR2, 5786 6p) containing the 792 by fragment revealed higher efficiency of marker rescue compared to pGEM-T-2. The nptII fragments resulted in lower efficiencies compared to plasmid DNA containing the same fragment. For the 792 by fragment and the linearized plasmid pMR2 a first-order dependency of the frequency of marker rescue transformation on the DNA concentration was observed. Based on the acquired data, the hypothetical frequency of transformation of transgenic DNA to B. subtilis in cooked potatoes was calculated to be equal to 8.5 x 10(-19) and 1.2 x 10(-27) for homologous and illegitimate recombination, respectively. These data permit to roughly estimate the time after which a person (101 years) or the world population (15 days) is exposed to one transformant generated by homologous recombination event, when the daily consumption per person is 130 g of cooked potatoes.