[Change in the structural organization of Mycobacterium rubrum cells upon the action of ethidium bromide]

The action of ethidium bromide on Mycobacterium rubrum cells was studied. The culture growth was found to depend on ethidium bromide (EB) concentration in the medium. The reaction of EB with nucleoid DNA was shown to be specific and changes in the nucleoid structure were detected. Low EB doses (ca. 2 micrograms/ml) caused DNA despiralization in many cells. The process was reversible, which accounted for the elevated ability of reactivation at low EB doses. A higher EB dose (ca. 5-10 micrograms/ml and more) made the nucleoid structure coarser and denser in most cells and the nucleoid broke down to small fragments. As a result, due to the pool of enzymes present in the cells prior to EB addition, secondary changes developed. They involved all the cellular structures as well as the metabolism of lipids, polyphosphates, and glycogen. As a rule, these changes were incompatible with the cell viability.