Study On The Physiological Characteristics Of Two Saccharomyces Cerevisiae Mutants Impaired In Respiration

Through comparison of fermentative capacities of the strains grown on high-sugar content media,we found that compared to MF1002,the growth rate and budding percentage of MF11a and MF15c, mutants of high-yield Saccharomyces cerevisiae MF1002for alcohol fermentation of sugarcane molasses, increased obviously and the cell death rate of the mutants decreased in the medium with30%and40%glucose,which suggested MF1la and MF15c could tolerate higher glucose than MF1002.To investigate the tolerant mechanism of MF11a and MF15c induced by high sugar level,the change of plasma membrane permeability and cellular biochemical characterization in30%glucose medium was studied.The result showed that the plasma membrane permeability and catalase of MF15c was lower than which of MF1002.The activity of total superoxide dismutase, peroxidase, cytoplasmic ATPase, mitochondrial ATPase and the trehalose content of MF15c were higher than MF1002, which suggested that tolerance of MF15C is related to the physiological characteristics including membrane integrity, increased activity of total superoxide dismutase, peroxidase, cytoplasmic ATPase, mitochondrial ATPase and trehalose content.The activity of peroxidase, catalase, cytoplasmic ATPase and the trehalose content of MF11a were higher than which of MF1002.However, the the plasma membrane permeability of MFlla was higher than MF1002. The activity of total superoxide dismutase and mitochondrial ATPase of MF11a was lower than MF1002. Therefore, the tolerant mechanism of MF11a was different from MF15c. The data suggested that tolerance of MF11a is related to the physiological characteristics including increased activity of catalase, peroxidase, cytoplasmic ATPase and trehalose content.Moreover, the result of microscopic observation indicated that cellular and mitochondrial morphological characteristics of two mutants had no obvious difference from MF1002. We determined the activity of cytochrome c oxidase the and the relative respiration rate of isolated mitochondria of the mutants through analysis of colorimetric reaction of2,3,5-Triphenyl Tetrazolium Chloride (TTC). The result suggested that the mitochondrial respiration rate and the activity of cytochrome c oxidase of MF11a and MF15c were higher than MF1002. So MF11a and MF15c were new respiratory mutants that different from the preceding reports, the impaired respiration is not related to mitochondrial respiratory chain deficiency.