Increased stability of maintenance of pAT153 in Escherichia coli HB101 due to transposition of IS1 from the chromosome into the tetracycline resistance region of pAT153

Abstract The plasmid vector pAT153 was rapidly lost from carbon-limited continuous cultures of Escherichia coli HB101 (pAT153) at a dilution rate of 0.15 h⁻¹. In one experiment, the plasmid was maintained by 80% of the host bacteria for up to 35 generations. The tetracycline-resistance gene was not expressed from the majority of the plasmid DNA in this population of E. coli HB101 due to transposition of IS1 from the bacterial chromosome into the aminoterminal region of the tet gene of pAT153. This plasmid, pLCX1, when isolated and retransformed into E. coli HB101, was more stably maintained than pAT153. Similar plasmids have been isolated from other glucose, phosphate, ammonium and sulphate-limited chemostats.