Stable maintenance in chemostat-grown Escherichia coli of pBR322 and pACYC184 by disruption of the tetracycline resistance gene*

Plasmid stability was studied in antibiotic-free chemo-stat cultures. Disruption, either by deletion or insertion, of the tetracycline resistance gene in the EcoRl/EcoRV region of the cloning vector pBR322 or in the HindIII]BamHl region of pACYCI84 yields plasmids markedly more stable than the parent plasmids. Thus, at least for these two instances, cloning of a partitioning (par) locus is not prerequisite for plasmid maintenance.