Application of temperature-sensitive mutants for single-cell protein production

Cell-division-cycle, temperature-sensitive mutants of Saccharomyces cerevisiae were investigated as a means of altering the morphological characteristics and subsequent physical properties of single-cell protein (SCP). Strain 4471, harboring mutation cdc 4, formed a visible complex mass at the nonpermissive temperature, after being grown at 30°C and then transferred to 37°C for 8 hr. Microscopic observation showed that the mother cell was unable to complete the budding process at the nonpermissive temperature, which caused the cells to enlarge. Viscosity measurements were used to establish and characterize optimum morphological changes in the yeast. The Maximum increase in viscosity occurred when cells were incubated at 30°C and then shifted to 37°C for 8 hr. Strain 4471 exhibited yield stress, whereas A364A did not. Maximum change in yield stress occurred when cells were shifted from 30 to 37°C for 8 hr. No significant loss of protein or RNA occurred in strain 4471, as compared to strain A364A, when incubated at the nonpermissive temperature.