PURPOSE: To produce the titled yeast strain having excellent workability and freeze resistance, by irradiating an artificial diploid cell of yeast belonging to Torulaspora genus with ultraviolet radiation to form an artificial triploid cell and separating a strain free from neutritional mutation.
CONSTITUTION: An artificial diploid strain of Torulaspora delbrucckii which is a yeast belonging to Torulaspora genus is suspended in a sterilized solution of about 67mM of KH2PO4, etc., at a cell concentration of about 105 cells per ml. About 10ml of the obtained cell suspension is irradiated with ultraviolet radiation at a dose of about 2,000erg/sec/cm2 to increase the ploidy of the chromosome of the cell and to form an artificial triploid. A small amount of the treated suspension is inoculated on an agar plate such as YPD medium and cultured for about 2 days at about 30°C. Grown colony having a survival ratio of 2W10% is fished and subjected to microscopic examination and an extra-large cell strain free from neutritional mutation is separated and purified to obtain grown polyploid extra-large cell strain.
OOSHIMA YOSHIYASU
SUGAURA TOSHIO
