Engineering high‐gravity fermentations for ethanol production at elevated temperature with Saccharomyces cerevisiae. Issue 10 (21st July 2019)

• Record Type: Journal Article
• Authors: Caspeta, Luis; Coronel, Jesús; Montes de Oca, Arturo; Abarca, Eduardo; González, Lidia; Martínez, Alfredo
• Is Part Of: Biotechnology and bioengineering. Volume 116:Issue 10(2019)
• Page Start: 2587
• Page End: 2597
• Publication Date: 2019-07-21
• Subjects: ethanol tolerance -- high‐temperature fermentation -- S. cerevisiae -- thermotolerance; Biotechnology -- Periodicals; Bioengineering -- Periodicals; 660.6
• DOI: 10.1002/bit.27103
• Languages: English
• ISSNs: 0006-3592

Abstract

Abstract: Thermal damage, high osmolarity, and ethanol toxicity in the yeast Saccharomyces cerevisiae limit titer and productivity in fermentation to produce ethanol. We show that long‐term adaptive laboratory evolution at 39.5°C generates thermotolerant yeast strains, which increased ethanol yield and productivity by 10% and 70%, in 2% glucose fermentations. From these strains, which also tolerate elevated‐osmolarity, we selected a stable one, namely a strain lacking chromosomal duplications. This strain (TTY23) showed reduced mitochondrial metabolism and high proton efflux, and therefore lower ethanol tolerance. This maladaptation was bolstered by reestablishing proton homeostasis through increasing fermentation pH from 5 to 6 and/or adding potassium to the media. This change allowed the TTY23 strain to produce 1.3–1.6 times more ethanol than the parental strain in fermentations at 40°C with glucose concentrations ~300 g/L. Furthermore, ethanol titers and productivities up to 93.1 and 3.87 g·L −1 ·hr −1 were obtained from fermentations with 200 g/L glucose in potassium‐containing media at 40°C. Albeit the complexity of cellular responses to heat, ethanol, and high osmolarity, in this study we overcome such limitations by an inverse metabolic engineering approach. Abstract : The inverse metabolic engineering approach was used to engineer a high‐gravity fermentation for ethanol production at high‐temperature. First, thermotolerant yeast strains were selected from ALE experiments after 1, 200 generations to avoid chromosomal duplications. The ability of these strains to tolerate different stresses was evaluated, along with the transcriptional profiling of one selected strain. These analyses let us seek for fundamental mechanisms of thermal tolerance. Finally, this information was used to fix fermentation operation and improve ethanol production at high temperature.