Biochemical Effects of Ethidium Bromide in Micro-organisms

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Abstract
SUMMARY: Growth of Escherichia coli was partially inhibited by 1.2 x 10-4 m-ethidium bromide, a phenanthridinium trypanocide. In the presence of manganese the drug's effect was decreased. During growth in the presence of ethidium, RNA and protein contents were relatively unaffected when comparison was made between experimental and control cultures at similar turbidities; DNA content, on the other hand, was considerably decreased. A differential effect of ethidium on the formation of polynucleotide pyrimidines from labelled uracil and orotic acid was observed. Oxygen uptake continued almost unchanged during growth whether in the presence or absence of drug. Bacillus cereus was extremely sensitive to the growth-inhibitory action of ethidium (10-5 m) and morphological changes were observed. Manganese protected the organisms from the drug's actions. RNA and DNA biosynthesis were both suppressed during inhibition of growth to a greater extent than was total protein formation, whereas diaminopimelic acid incorporation into cell wall and oxygen uptake continued almost unaffected. Some evidence was obtained that the pattern of protein synthesis was disturbed. It was concluded that the drug's actions were species dependent, and that the effect on Escherichia coli resembled that described for a flagellate, while that on Bacillus cereus did not. Evidence for compartmentation of nucleic acid synthesis, as obtained with the drug in tumour cells, was not shown for either micro-organism.