Ethidium bromide-resistant mutant of Bacillus subtilis.

An ethidium bromide-resistant mutant (EB8) derived from a Marburg strain of Bacillus subtilis was found to be conditionally resistant to 10 mug of ethidium bromide per ml. Expression of resistance is complete only during vegetative growth at incubation temperatures above 30 C in complex medium or minimal medium supplemented with Casamino Acids. Strain EB8 is cross-resistant to acriflavine and proflavine. The ethidium bromide resistance marker is co-transduced with hisA1 at a frequency of 6% and is located to the right of hisA1 on the B. subtilis chromosome as it is usually represented on the map. Incorporation of [5-(3)H] uridine by strain EB8 showed that ribonucleic acid synthesis in both whole cells and protoplasts is ethidium bromide-resistant.