Systematic Analysis On Ethanol Fermentation Under Higher Cell Density

High cell density fermentation is effective in increasing the productivity of the product and in shortening the fermentation cycle.However,when the cell density in the culture was too high,it would be stressfull to the cells and harmful to cell growth and function.In this paper,high cell density fermentation was applied to Saccharomyces cerevisiae for ethanol production.Yeast was fermented at the pitching rates of 1gram,5grams,10 grams,20grams,and 40 grams of dry yeast per liter.Using system biotechnology,the influences of innolulum size to the cells were investigated at the platforms of lipidomics,metabolomics,and proteomics.Compared the capacity of the yeast at the 5 pitching rates,it was found that cells with higher pitching rates entered exponential phase easier than lower pitching rates.High cell density fermentation reduced net growth of the yeast but increased production of the target product ethanol and the byproduct glyerol.Lipidomics indicated that the synthesis of PI was inhibited,while the synthsis of PS and PG was enhanced,owning to the reduced insitol in high cell density fermentation.To adapt to the high cell density condition,the physicochemical properties of membrane was modulated by reduced the synthesis of saturated phospholipids and phospholipids with shorter chains.Ergosterol,which was protective in the cell,was synthesizedfor a great mount.Metabolomics revealed that the citric acid cycle was suppressed in fermentation with higher cell density.Protective molecules such as glycerol and proline were synthsized in high cell density conditions.Myo-inositol and ethanolamine were reduced,which were agree with the results of lipids.Proteomics analysis showed that cells in high cell density fermentation were exposed to virious stress such as thermo stress and oxidative stress.Chaperones encoded by heat shock genes,as well as variationsof some essential proteins,play critical roles inresponses of S.cerevisiae to inoculation size.