Breeding Of Two Respiration-impaired Mutants Of Saccharomyces Cerevisiae With Enhanced Sugar Metabolism Capacity

Two phenotype stable respiration-impaired mutants, named as MF15c and MFlla, were selected by UV-ray inducing a high-ethanol-producing industrial strain MF1002of Saccharomyces cerevisiae. The relative respiration rate of mutants, determined through analysis of colorimetric reaction of2,3,5-Triphenyl Tetrazolium Chloride (TTC) in the cells, was only57.77%and47.25%of MF1002respectively. Unlike the most previously reported mutation, both mutants were with the novel phenotypes that the growth rate was not significant different from the parent strain, and no "petite colonie" were observed on YPD plate cultivation. However, the fermentation with sucrose as substrate showed that, comparing with MF1002, the ethanol yield of mutants were only slightly enhanced6.48～6.59%(MF15c)and1.66-1.97%(MFlla), but the content of total residual sugar of mutants were significantly decreased34.85%(MF15c) and19.70%(MF11a), the fermentation efficiency of mutants were also significantly enhanced6.69%and4.71%respectively, indicating MF15c and MF11a were novel respiration-impaired mutants. Since enhancing the sugar metabolism capacity and the fermentation efficiency involves a significant benefit for ethanol fermentation, we argue that both mutants have a great potential utilization value for ethanol production.The fermentation with ugarcane molasses as substrate showed that, comparing with MF1002, the ethanol yield of mutants was improved. By using the fermentation process of ethanol production from sugarcane molasses, in the termination of the fermentation, the content of total residual sugar of mutants were significantly reduced16.82%(MF15c) and10.14%(MF11a) comparing with MF1002. We argue that the two mutants have a great potential utilization value for ethanol production.In addition, we studied the ethanol tolerance capacity of the strains. We also investigated the activity of key enzymes in glycolytic pathway, citric acid cycle and other key metabolic pathways, the results will lay a foundation for the further study of the mechanism of the performance of high sugar utilization of the mutants.