STABILITY OF A RECOMBINANT PLASMID CONTAINING ALPHA-AMYLASE GENE IN CHEMOSTAT

Continuous cultivation of Escherichia coli harboring a recombinant plasmid containing alpha -amylase gene was carried out, and the stability of the plasmid was examined under different cultivation conditions. E. coli maintained the plasmid stably when grown in L-broth medium. Production of alpha -amylase, however, decreased as the dilution rate increased. When the cells were grown in a synthetic medium (Davis medium) supplemented with glucose as a carbon source, the plasmid was unstable. Plasmid-free organisms, organisms harboring a plasmid having a deletion in alpha -amylse gene and organisms harboring the plasmid whose copy numbers decreased appeared along with organisms harboring an intact plasmid. When starch was used as a carbon source, the plasmid was reasonably stable.