Abstract
BackgroundThe optimization of industrial bioethanol production will depend on the rational design and manipulation of industrial strains to improve their robustness against the many stress factors affecting their performance during very high gravity (VHG) or lignocellulosic fermentations. In this study, a set of Saccharomyces cerevisiae genes found, through genome-wide screenings, to confer resistance to the simultaneous presence of different relevant stresses were identified as required for maximal fermentation performance under industrial conditions.ResultsChemogenomics data were used to identify eight genes whose expression confers simultaneous resistance to high concentrations of glucose, acetic acid and ethanol, chemical stresses relevant for VHG fermentations; and eleven genes conferring simultaneous resistance to stresses relevant during lignocellulosic fermentations. These eleven genes were identified based on two different sets: one with five genes granting simultaneous resistance to ethanol, acetic acid and furfural, and the other with six genes providing simultaneous resistance to ethanol, acetic acid and vanillin. The expression of Bud31 and Hpr1 was found to lead to the increase of both ethanol yield and fermentation rate, while Pho85, Vrp1 and Ygl024w expression is required for maximal ethanol production in VHG fermentations. Five genes, Erg2, Prs3, Rav1, Rpb4 and Vma8, were found to contribute to the maintenance of cell viability in wheat straw hydrolysate and/or the maximal fermentation rate of this substrate.ConclusionsThe identified genes stand as preferential targets for genetic engineering manipulation in order to generate more robust industrial strains, able to cope with the most significant fermentation stresses and, thus, to increase ethanol production rate and final ethanol titers.
Highlights
The optimization of industrial bioethanol production will depend on the rational design and manipulation of industrial strains to improve their robustness against the many stress factors affecting their performance during very high gravity (VHG) or lignocellulosic fermentations
Identification of Saccharomyces cerevisiae genes involved in tolerance to relevant stresses in VHG alcoholic fermentations or in biomass-based fermentations To identify yeast genes that simultaneously confer resistance to inhibitory concentrations of ethanol, glucose and acetic acid or to acetic acid, ethanol, vanillin and/or furfural, we used the results of genome-wide phenotypic screenings carried out in the presence of those stressors [15,16,17,18,19]
These studies were not performed using the BY4741 strain, which was the one used to screen the determinants of tolerance to furfural, vanillin and high glucose concentrations [16,18,19], and they were not considered because the genetic background of the yeast strain used is known to have a high impact on the results obtained in large-scale phenotype screenings
Summary
The optimization of industrial bioethanol production will depend on the rational design and manipulation of industrial strains to improve their robustness against the many stress factors affecting their performance during very high gravity (VHG) or lignocellulosic fermentations. Most of the current processes of bioethanol production are based on the use of very high gravity (VHG) fermentations in which highly raw materials have to be subjected to a pre-treatment and hydrolysis, during which mostly hemicellulose sugars are released. Other inhibitory products include acetic acid, which derives from heavily acetylated polymers and is released during pre-treatment and hydrolysis. The current knowledge on the mechanisms underlying yeast tolerance to the toxicants present in lignocellulose hydrolysates fermentation, based on molecular studies and genome-wide approaches, was recently reviewed by Liu [9]
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