Response mechanisms of Saccharomyces cerevisiae to the stress factors present in lignocellulose hydrolysate and strategies for constructing robust strains

Abstract

Bioconversion of lignocellulosic biomass to biofuels such as bioethanol and high value-added products has attracted great interest in recent decades due to the carbon neutral nature of biomass feedstock. However, there are still many key technical difficulties for the industrial application of biomass bioconversion processes. One of the challenges associated with the microorganism Saccharomyces cerevisiae that is usually used for bioethanol production refers to the inhibition of the yeast by various stress factors. These inhibitive effects seriously restrict the growth and fermentation performance of the strains, resulting in reduced bioethanol production efficiency. Therefore, improving the stress response ability of the strains is of great significance for industrial production of bioethanol. In this article, the response mechanisms of S. cerevisiae to various hydrolysate-derived stress factors including organic acids, furan aldehydes, and phenolic compounds have been reviewed. Organic acids mainly stimulate cells to induce intracellular acidification, furan aldehydes mainly break the intracellular redox balance, and phenolic compounds have a greater effect on membrane homeostasis. These damages lead to inadequate intracellular energy supply and dysregulation of transcription and translation processes, and then activate a series of stress responses. The regulation mechanisms of S. cerevisiae in response to these stress factors are discussed with regard to the cell wall/membrane, energy, amino acids, transcriptional and translational, and redox regulation. The reported key target genes and transcription factors that contribute to the improvement of the strain performance are summarized. Furthermore, the genetic engineering strategies of constructing multilevel defense and eliminating stress effects are discussed in order to provide technical strategies for robust strain construction. It is recommended that robust S. cerevisiae can be constructed with the intervention of metabolic regulation based on the specific stress responses. Rational design with multilevel gene control and intensification of key enzymes can provide good strategies for construction of robust strains.

Keywords: Lignocellulosic biomass; Robust strain construction; Stress factor; Stress response; Target genes.

Fig. 1

Main stress factors involved in production of lignocellulosic bioethanol by bioconversion

Fig. 2

Endogenous regulation mechanisms of S. cerevisiae in response to stress factors

Fig. 3

Schematic diagram of the multilevel defense of S. cerevisiae to different stress factors, including cell wall signals cascade, plasma membrane barrier, central carbon and amino acid metabolism, and intracellular redox homeostasis

Fig. 4

Possible strategies to construct robust S. cerevisiae. The response performance of S. cerevisiae to stress factors can be improved with the construction of the tolerant and eliminated pathway in cell. The expression of the single/multiple genes circuit induces the rewriting of the endogenous regulation of S. cerevisiae. Assisting in adaptive evolution to balance the metabolic load of strain can further promote the improvement of S. cerevisiae robustness