Comparative Lipidomics Studies Of Different Strains Of Saccharomyces Cerevisiae During The Process Of Cellulosic Ethanol Production

The inhibitor tolerant capacity and the capability of utilizing xylose for S. cerevisiae are two key issues in the process of cellulosic ethanol production. In order to investigate the mechanism of inhibitor tolerance for S. cerevisiae and the factors influencing the catabolism of xylose, high-throughput lipidome analyzing protocol together with bioinformatics strategy were used to study an industrial baker's yeast (SC) strain from Angel Yeast Corp., a phenol tolerant strain (SCP), a furfural tolerant strain (SCF), an acetic acid tolerant strain (SCA), a recombinant xylose fermenting strain 424A(LNH-ST), and native strain 4124.Phospholipid profile was obtained using the LC/ESI/MSn strategy. Totally 120 kinds of phospholipids were identified, including 9 species of phosphatidylglycerol (PG), 24 species of phosphatidylethanolamine (PE), 25 species of phosphatidylcholine (PC), 30 species of phosphatidylinositol (PI), 17 species of phosphatidylserine (PS), and 15 species of phosphatidic acid (PA). Wavelet transform (WT) was integrated with traditional pattern recognition methods and the new method wavelet transform-principal component analysis (WT-PCA) had strong pattern recognition capacities. WT-PCA was then applied to mine the lipidome data for S. cerevisiae and the differences between phospholipids profiles for different S. cerevisiae strains were analyzed.The addition of furfural led to higher levels of PC together with lower levels of PE and PI for both SC and furfural tolerant strain SCF. Phenol increased the levels of PC while decreased the levels of PE and PI for both SC and phenol tolerant strain SCP. Acetic acid increased the relative abundance of PA and PS whereas decreased the relative amount of PI for both SC and acetic acid tolerant strain SCA. Comparative lipidomic study revealed PC, PI, and PA as biomarkers for discriminating SCF, SCP, and SCA from SC strain, respectively. Further analysis revealed that the saturation levels for PC molecules were higher in SCF than that in SC. Strain SCP possessed less PI molecules with short hydrocarbon chains and more PI molecules with long chains. Both the length of hydrocarbon chains and the saturation levels for PA molecules showed great difference between SC and SCA. The changes of saturation levels and the length of hydrocarbon chains can both influence the membrane fluidity, indicating that the changes of membrane fluidity played important roles in the process of inhibitor tolerance. When comparing different inhibitors, it was found that the higher the logPow is, the more toxic the compound will be. It was believed that the toxicity of furfural and phenol was related to their lipophilic nature whereas the toxicity of acetic acid was mainly caused by pH change.The fermentation behavior and the corresponding lipidome data for strain 424A(LNH-ST) and its native strain 4124 were investigated. It was found out that the xylose uptaking rate was influenced by both inhibitory compounds and the available nutrients in medium. What was more, the phospholipids composition was closely related to the fermentation performance of S. cerevisiae. Higher PI/PS ratio was always accompanied by higher stationary phase cell density, PC/PE ratio had similar trends with the utilization rates of glucose, and the contents of PI were closely related to xylose uptaking rates. These findings indicate that the changes of the membrane properties followed by the changes of phospholipids may further influence the transportation rates and finally the utilization rates of sugars. The changes of cell viability indicated by membrane phospholipids change also influenced the process of xylose catabolism.