Indexed on: 01 Dec '74Published on: 01 Dec '74Published in: Molecular & general genetics : MGG
In cultures of Escherichia coli K-12 or Salmonella typhimurium LT2 carrying the extra-chromosomal plasmid, colicin factor E2-P9, the incidence of cells forming colicin varied spontaneously between a minimum of ca. 0.01% in the exponential phase of growth and a maximum of ca. 75% in the stationary phase. The number of copies of the plasmid per chromosome remained constant throughout, judging from direct measurement of plasmid DNA and from transduction frequencies. The changes observed therefore reflect changes in the frequency with which each copy is expressed. Individual copies of the colicin factor in a given cell are probably expressed simultaneously, not independently. Colicin producing cells, although killed, do not disintegrate during several hours of incubation.