HIGH-EFFICIENCY ELECTROTRANSFORMATION OF THE YEAST SCHWANNIOMYCES-OCCIDENTALIS

A method has been developed for introducing heterologous DNA rapidly and efficiently by electropermeabilization into the yeast Schwanniomyces occidentalis. A transformation efficiency as high as 2x10(5) transformants/mu g of plasmid DNA was obtained with a square-wave electric pulse of 2.17 kV/cm during 18 ms. Small quantities of DNA (5 ng) can be used to transform 3x10(8) cells. The main parameters which have been optimized are: presence of adenine in the culture medium, pretreatment of the cells with dithiothreitol during the exponential growth phase of the cells, amount of cells treated, and pulse-field strength and duration. Competent cells can be stored to allow electrotransformation whenever needed.