Microbiological implications of electric field effects. III. Stimulation of yeast protoplast fusion by electric field pulses.

Prototrophic colonies could be selected on minimal medium after mixing of protoplasts from diauxotrophic mutants of the yeasts Saccharomycopsis lipolytica and/or Lodderomyces elongisporus and treatment with polyethylene glycol (PEG) in the presence of calcium chloride. This is the result of protoplast fusion and complementation of auxotrophic deficiencies. Under identical conditions an electric field pulse in the mus-range applied via an electric discharge to the protoplast-PEG mixture resulted in a drastic enhancement of the protoplast fusion rate. The presence of polyethylene glycol was demonstrated to be a prerequisite for fusion in this case, too. The frequency of hybrid formation detected a prototrophic colonies could be increased in the case of intraspecific fusion at initial electric field strengths between 2.5 and 5 kV . cm-1. The application of an electric field pulse of proper strength and duration to a yeast protoplast suspension turned out to be a more effective tool in production of fusion products that conventional methods. Large numbers of parasexual hybrids for different selection programmes in yeast genetics and for industrial purpose may be delivered by this technique.