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Comparison of Deoxyribonucleic Acid Uptake and Marker Integration in Bacilli and Protoplasts of Bacillus subtilis

^a Department of Microbiology, Northwestern State University of Louisiana, Natchitoches, Louisiana 71457, and Department of Biology, Georgetown University, Washington, D.C. 20007

ABSTRACT

trp⁺his^– donor deoxyribonucleic acid (DNA) was added to highly competent trp^–his⁺ recipient bacilli and to protoplasts prepared from these bacilli, and the cell-DNA complexes were incubated for 30 min. The complexes were then washed and lysed, and their DNA was analyzed on a trp^–his^– strain for the donor marker trp⁺, the resident marker his⁺, and for the recombinant trp⁺his⁺ combination. The extracts of the bacillary complexes contained a normal percentage of donor markers (0.1-0.2%), and the number of trp⁺his⁺ doubles (20% of all trp⁺ transformants) indicated that the donor DNA had become integrated into the resident genomes. The protoplast complexes contained 10 to 1,000 times fewer donor markers and almost no recombinants. This indicated that, in protoplasts, marker uptake was minimal and recombination was absent. Uptake was also measured with ³H-labeled DNA. On the average, protoplasts took up one-fiftieth as much DNA as bacilli. It was concluded that, probably, protoplasts took up no DNA at all, that there were no DNA affinity sites on the surface of the protoplasts, and that the residual marker and radioactivity uptake was due to imperfections in the experimental system. The data and conclusions differed sharply from earlier ones of Hirokawa and Ikeda despite the fact that the techniques of these authors were followed in repeat experiments.

¹ Present address: Haifa Absorption Center, Haifa, Israel.