The elimination of extrachromosomal elements in thymineless strains of Escherichia coli K12

Abstract

Strains of E. coli carrying extrachromosomal elements (F sex factors and colicin factors) were subjected to standard acridine orange treatment. Wild type autonomous F (F+) and certain substituted F factors (F primes) were eliminated with high efficiency. There was no elimination of colicin factors nor of a particular F prime factor (F13). Thymineless mutants of strains carrying these extrachromosomal elements were subjected to growth in suboptimal concentrations of thymine for 24 hours. Elimination of all factors was found among the survivors. Elimination of colicin factors was found only under more severe conditions of thymine deprivation. All F factors (wild type and substituted) were eliminated with high efficiency to about the same extent but there was no elimination of integrated F factors from Hfr strains. The elimination of a series of factors from the same strain seemed to occur independently.