Immunization of the industrial fermentation starter culture strain of Saccharomyces cerevisiae to a contaminating killer toxin-producing Candida tropicalis Original Research Article

K3 killer trait was introduced into the fermentation starter strain of Saccharomyces cerevisiae BSP 1 in order to construct immune industrial strain that produces K3 type killer toxin and was resistant to Candida tropicalis (K+) contamination. Protoplasts of respiration-deficient Rhoo strain of S. cerevisiae NCYC 761 (K3) and S. cerevisiae BSP 1 were fused. The resulting respiration-competent hybrid with K3 type killer activity was selected on media containing a non-fermentable carbon source and by a killer zone assay in a plate test, respectively. The fusant was similar to the parent strain in its fermentation and sugar utilization patterns, growth rate, dough-raising properties and osmotolerance. The newly constructed S. cerevisiae BSP 1 (K3) inhibited the growth of C. tropicalis in a pH range from 3.5 to 5.0 and over a temperature range of 20–30°C.