Robust industrial Saccharomyces cerevisiae strains for very high gravity bio-ethanol fermentations.

The application and physiological background of two industrial Saccharomyces cerevisiae strains, isolated from harsh industrial environments, were studied in Very High Gravity (VHG) bio-ethanol fermentations. VHG laboratory fermentations, mimicking industrially relevant conditions, were performed with PE-2 and CA1185 industrial strains and the CEN.PK113-7D laboratory strain. The industrial isolates produced remarkable high ethanol titres (>19%, v/v) and accumulated an increased content of sterols (2 to 5-fold), glycogen (2 to 4-fold) and trehalose (1.1-fold), relatively to laboratory strain. For laboratory and industrial strains, a sharp decrease in the viability and trehalose concentration was observed above 90 g l⁻¹ and 140 g l⁻¹ ethanol, respectively. PE-2 and CA1185 industrial strains presented important physiological differences relatively to CEN.PK113-7D strain and showed to be more prepared to cope with VHG stresses. The identification of a critical ethanol concentration above which viability and trehalose concentration decrease significantly is of great importance to guide VHG process engineering strategies. This study contributes to the improvement of VHG processes by identifying yeast isolates and gathering yeast physiological information during the intensified fermentation process, which, besides elucidating important differences between these industrial and laboratory strains, can drive further process optimization.

Pereira FB ，Guimarães PM ，Teixeira JA ，Domingues L ... -  《-》

Selection of Saccharomyces cerevisiae strains for efficient very high gravity bio-ethanol fermentation processes.

Pereira FB ，Guimarães PM ，Teixeira JA ，Domingues L ... -  《-》

Cell recycling during repeated very high gravity bio-ethanol fermentations using the industrial Saccharomyces cerevisiae strain PE-2.

Pereira FB ，Gomes DG ，Guimarães PM ，Teixeira JA ，Domingues L ... -  《-》

Relationship of trehalose accumulation with ethanol fermentation in industrial Saccharomyces cerevisiae yeast strains.

The protective effect and the mechanisms of trehalose accumulation in industrial Saccharomyces cerevisiae strains were investigated during ethanol fermentation. The engineered strains with more intercellular trehalose achieved significantly higher fermentation rates and ethanol yields than their wild strain ZS during very high gravity (VHG) fermentation, while their performances were not different during regular fermentation. The VHG fermentation performances of these strains were consistent with their growth capacity under osmotic stress and ethanol stress, the key stress factors during VHG fermentation. These results suggest that trehalose accumulation is more important for VHG fermentation of industrial yeast strains than regular one. The differences in membrane integrity and antioxidative capacity of these strains indicated the possible mechanisms of trehalose as a protectant under VHG condition. Therefore, trehalose metabolic engineering may be a useful strategy for improving the VHG fermentation performance of industrial yeast strains.

Wang PM ，Zheng DQ ，Chi XQ ，Li O ，Qian CD ，Liu TZ ，Zhang XY ，Du FG ，Sun PY ，Qu AM ，Wu XC ... -  《-》

Optimization of low-cost medium for very high gravity ethanol fermentations by Saccharomyces cerevisiae using statistical experimental designs.

Statistical experimental designs were used to develop a medium based on corn steep liquor (CSL) and other low-cost nutrient sources for high-performance very high gravity (VHG) ethanol fermentations by Saccharomyces cerevisiae. The critical nutrients were initially selected according to a Plackett-Burman design and the optimized medium composition (44.3 g/L CSL; 2.3 g/L urea; 3.8 g/L MgSO₄·7H₂O; 0.03 g/L CuSO₄·5H₂O) for maximum ethanol production by the laboratory strain CEN.PK 113-7D was obtained by response surface methodology, based on a three-level four-factor Box-Behnken design. The optimization process resulted in significantly enhanced final ethanol titre, productivity and yeast viability in batch VHG fermentations (up to 330 g/L glucose) with CEN.PK113-7D and with industrial strain PE-2, which is used for bio-ethanol production in Brazil. Strain PE-2 was able to produce 18.6±0.5% (v/v) ethanol with a corresponding productivity of 2.4±0.1g/L/h. This study provides valuable insights into cost-effective nutritional supplementation of industrial fuel ethanol VHG fermentations.

Pereira FB ，Guimarães PM ，Teixeira JA ，Domingues L ... -  《-》