Breeding of a non-urea producing sake yeast with killer character using a kar1-1 mutant as a killer donor

Arginase-deficient (car1/car1) sake yeasts can brew sake without urea, a ma in precursor of ethyl carbamate, which is a suspected carcinogen in various fermented beverages, For the use of car1/car1 yeasts in sake production, c ontamination by wild-type (CAR1/CAR1) yeasts is a major problem, To protect sake mash against such contamination, killer character was introduced into the car1/car1 sake yeast HL163 by rare mating and protoplast fusion, using a karl-l haploid harboring killer dsRNA plasmids as a killer donor, All ki ller yeasts obtained showed no arginase activity and the same DNA content p er cell as strain HL163, and produced sake with ordinary quality and very l ow levels of urea. We also demonstrated that one of these killer yeasts cou ld effectively eliminate contaminant cells of a CAR1/CAR1 yeast from sake m ash.