Plasmid copy number and mutant frequencies ins. typhimurium ta102

Abstract
Tetracycline and chloramphenicol increase the number of mutant colonies of strain TA102, which carries the reverting gene on die plasmid pAQ1. Determination of the plasmid content by agarose gel analysis shows that the increase of the mutant colony number is paralleled closely by an increase of die number of pAQ1 plasmids per cell, indicating mat the two compounds do not increase the frequency of mutants “per gene,” but only enhance the number of the genes at which mutations can occur. Thus, not considering die molecular processes could result in mistakenly attributing the increase in the number of mutants per plate (respective to the number of mutants per cell) to a mutagenic activity of die antibiotics.

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