The lesions induced in Bacillus subtilis deoxyribonucleic acid (DNA) after treating bacterial cells (in vivo) and bacterial DNA (in vitro) with chloramine were studied biologically and physically. Single-strand breaks and a few doublestrand scissions (at higher chloramine doses) accompanied loss of DNA-transforming activity in both kinds of treatments. Chloramine was about three times more efficient in vitro than in vivo in inducing DNA single-strand breaks. DNA was slowly chlorinated; the

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... quent efficiency of producing DNA breaks was high. Chlorination of cells also reduced activity of endonucleases in cells; however, chlorinated DNA of both treatments was sensitized to cleavage by endonucleases. The procedure of extracting DNA from cells treated with chloramine induced further DNA degradation. Both treatments introduced a small fraction of alkali-sensitive lesions in DNA. DNA chlorinated in vitro showed further reduction in transforming activity as well as further degradation after incubation at 50 C for 5 h whereas DNA extracted from chloramine-treated cells did not show such a heat sensitivity. MATERIALS AND METHODS Bacterial strains. All strains used in this article were derivatives of indole-requiring B. subtilis strain 168 (14). Cell preparation. Cells grown overnight in 5 ml of Penassay broth were centrifuged and suspended in 50 ml of Spizizen minimal medium [per liter contains: (NH4)2S04, 2 g; K2HPO4, 14 g; Na citrate, 1 g; and MgSO4-7H20, 0.2 g] supplemented with 0.5% glucose, 0.05% casein hydrolysate, and 25 ,ug of those nutrients required for growth of auxotrophic 934 on May 9, 2020 by guest