EVALUATION OF SALT STRESS ADAPTATION ON GROWTH AND FERMENTATION CHARACTERISTICS OF YEAST IN INDUSTRIAL MEDIA

Abstract

The progressive transition to green economy and sustainable energy is a driver for the development of biofuels, a renewable fuel. My work focuses on improving the ethanol production of yeast cells using salt stress in industrial media. Saccharomyces cerevisiae, the most widely used commercial yeast for industrial ethanol production is used for the experimentation. The yeast strain used is S. cerevisiae CEN.PK 122 (diploid), which is an auxotrophic strain proven to exhibit double ethanol yield on biomass in high glucose concentration as compared to prototrophic strains due to selective transition of respiratory metabolism to fermentative metabolism. To further improve fermentation capacity of the yeast, salt stress is employed. The yeast cells are gradually adapted to high salt stress (3% NaCl) for three generations and tested for fermentative capacity in industrial grade corn steep liquor media using different seeding cell densities. It is found that once adapted to 3% salt stress, now salt adapted yeast cells are capable of improved fermentation and ethanol production on release of salt stress attributed to their enhanced growth as compared to unadapted yeast cells (control). Salt adapted yeast shows 1.5 times ethanol production than control. This enhanced fermentation by adapted cells occurs at higher cell density suggests molecular interaction and signalling among cells induced by salt stress to sense the environment and shift metabolic pathways for better adaptability and fermentation. There is metabolic modification of yeast using salt stress. Additionally, adaptation to one type of stress leads to protective response to other stress factors making salt stress adapted yeast ideal for use in industrial fermentation. The research paves way to solve the huge ethanol demand as biofuel by higher production in industrial media. Fermentation process accounts about 20% of the total production cost of bio-refineries that converts biomass to biofuel. Improved fermentation efficiency will decrease the price of ethanol biofuel, thus exploring native and overseas markets. This technology will revitalize Indian economy by decreased dependency on imported fuel and generating cheaper bioethanol fuel.