COMPARISON OF TECHNIQUES FOR MEASURING PLASMID STABILITY IN YEASTS

Three techniques for measuring plasmid stability in yeasts are describ ed and evaluated. The yeast used was a Kluyveromyces lactis strain whi ch was transformed with a plasmid, pCRI, to enable production of heter ologous alpha-amylase. The techniques were based on plate counts on a selective antibiotic-containing medium and a non-selective medium, and on clearing zones on starch-supplemented plates for alpha-amylase det ection. The plate ratio and clearing zones methods gave comparable res ults while the transfer colony method estimated much lower plasmid sta bilities.