Abstract:

Using Saccharomyces cerevisiae to ferment lignocellulosic biomass, thus realizing sustainable economic and social development, and has a good application prospect. However, the carboxylic acid, furfural and polyphenols from it have a strong inhibitory effect on S. cerevisiae. These inhibitors cause severe damages to organelles such as cell membranes, mitochondria and ribosomes, which affects the utilization of fermentable sugars in the hydrolysate by S. cerevisiae. This paper systematically reviews the signal pathways and metabolic pathways by which these three types of inhibitors exert stress on S. cerevisiae. For example, weak acids can induce intracellular acidification, and furfural and phenolic compounds can reduce the activity of intracellular redox enzymes and inhibit the translation process. Based on the above stress mechanisms, this paper deeply explores positive genetic methods, such as mutagenesis breeding, laboratory adaptive evolution, cell self-flocculation, and co-culture. These methods are used to mine key genes by phenotypic mutation combined with multi-omics analysis, so as to construct efficient strains. Meanwhile, reverse genetic methods are also elaborated, that is, genomic transformation using known functional genes and strain-directed breeding based on the CRISPR-Cas system. Among them, methods such as overexpressing the target gene in S. cerevisiae, gene knockout using CRISPR-Cas9, and gene regulation using CRISPRa/CRISPRi effectively regulate the expressions of key genes, thereby enhancing the tolerance performance of S. cerevisiae. On this basis, a comprehensive strategy combining high-throughput gene library with multi-pathway gene regulation can be used for key gene screening and multi-dimensional gene regulation on a large scale. In the future, strategies such as the combined analysis of gene expression and metabolic flux can be used to monitor the activities of key enzymes and the carbon flux changes in key metabolic pathways related to tolerance in real time, so as to better cope with the synergistic effects of multiple inhibitors on S. cerevisiae, and provide references and suggestions for S. cerevisiae to efficiently utilize lignocellulose for fermentation.

Key words: Saccharomyces cerevisiae, lignocellulosic hydrolysate, inhibitors, tolerance, response mechanism, genetic modification