Engineering high-gravity fermentations for ethanol production at elevated temperature with Saccharomyces cerevisiae

Area of Science:

• Biotechnology
• Industrial Microbiology
• Yeast Genetics

Background:

• Ethanol fermentation by Saccharomyces cerevisiae is limited by thermal damage, high osmolarity, and ethanol toxicity.
• Developing robust yeast strains is crucial for improving fermentation efficiency and economic viability.

Purpose of the Study:

• To generate thermotolerant yeast strains through adaptive laboratory evolution.
• To enhance ethanol yield and productivity by overcoming fermentation limitations.

Main Methods:

• Adaptive laboratory evolution at 39.5°C to develop thermotolerant yeast.
• Selection of a stable strain (TTY23) lacking chromosomal duplications.
• Optimization of fermentation conditions (pH, potassium addition) to improve ethanol tolerance and production.

Main Results:

• Thermotolerant yeast strains increased ethanol yield by 10% and productivity by 70% in initial fermentations.
• The TTY23 strain, with optimized conditions, produced 1.3-1.6 times more ethanol than the parental strain at 40°C and high glucose concentrations (~300 g/L).
• Achieved ethanol titers up to 93.1 g·L⁻¹ and productivities of 3.87 g·L⁻¹·hr⁻¹ under optimized conditions.

Conclusions:

• Adaptive laboratory evolution is an effective strategy for creating yeast strains with enhanced tolerance to fermentation stressors.
• Inverse metabolic engineering by adjusting fermentation pH and media composition can significantly boost ethanol production in robust yeast strains.
• This study presents a viable approach to overcome limitations in industrial ethanol fermentation using Saccharomyces cerevisiae.