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

Abstract

Prototrophic colonies could be selected on minimal medium after mixing of protoplasts from diauxotrophic mutants of t h e yeasts Saeeharomycopsis lipolytiea and/or Lodderomyees 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 a n electric field puke in t h e ps-range applied via an electric discharge t o t h e 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. T h e frequency of hybrid formation detected as prototrophic colonies could be increased in t h e case of intraspecific fusion at initial electric field strengths between 2.5 and 5 kV . cm-l. 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 than conventional methods. Largs numbers of parasexual hybrids for different selection programmes in yeast genetics and for induetrial purpose may be delivered by this technique. Taking into account this knowledge we started in 1978 with experiments on protoplast fusion in the PEG-Ca2+ system in order t o try to enhance thc fusion frequency of different yeast species by electric field pulse treatment. First positive results we of 10-5 to 10-4.