Abstract
Being a microbial host for lignocellulosic biofuel production, Saccharomyces cerevisiae needs to be engineered to express a heterologous xylose pathway; however, it has been challenging to optimize the engineered strain for efficient and rapid fermentation of xylose. Deletion of PHO13 (Δpho13) has been reported to be a crucial genetic perturbation in improving xylose fermentation. A confirmed mechanism of the Δpho13 effect on xylose fermentation is that the Δpho13 transcriptionally activates the genes in the non-oxidative pentose phosphate pathway (PPP). In the current study, we found a couple of engineered strains, of which phenotypes were not affected by Δpho13 (Δpho13-negative), among many others we examined. Genome resequencing of the Δpho13-negative strains revealed that a loss-of-function mutation in GCR2 was responsible for the phenotype. Gcr2 is a global transcriptional factor involved in glucose metabolism. The results of RNA-seq confirmed that the deletion of GCR2 (Δgcr2) led to the upregulation of PPP genes as well as downregulation of glycolytic genes, and changes were more significant under xylose conditions than those under glucose conditions. Although there was no synergistic effect between Δpho13 and Δgcr2 in improving xylose fermentation, these results suggested that GCR2 is a novel knockout target in improving lignocellulosic ethanol production.
Highlights
Lignocellulosic biofuels are renewable liquid-fuel alternatives owing to abundant feedstock availability and substantial CO2 emission reduction (Lynd, 2017)
The present study found that the pho13 effect on xylose fermentation was not observed in a couple of strains, and a loss-of-function mutation in GCR2 was responsible
GCR2 encoding the transcriptional activator of glycolytic genes was identified as a novel deletion target to improve xylose fermentation by S. cerevisiae, expressing a heterologous xylose pathway
Summary
Lignocellulosic biofuels are renewable liquid-fuel alternatives owing to abundant feedstock availability and substantial CO2 emission reduction (Lynd, 2017). Saccharomyces cerevisiae plays an essential role in the production of lignocellulosic biofuels by fermenting lignocellulosic sugars, mainly glucose and xylose, which requires engineering of the yeast via a heterologous xylose pathway (Kim et al, 2013c; Richa et al, 2019). Current efforts on the metabolic engineering of GCR2 Deletion for Xylose Metabolism yeast remain focused on improving the xylose fermentation yield and productivity under multiple stress conditions of lignocellulosic biomass hydrolyzates (Jeong et al, 2020; Qin et al, 2020). Continued efforts have discovered that the deletion of PHO13 ( pho13) resulted in transcriptional and metabolic changes favorable to xylose and other C5 sugar fermentation (Kim et al, 2015; Xu et al, 2016; Ye et al, 2019). The most advanced finding is that pho results in the transcriptional activation of non-oxidative pentose phosphate pathway (PPP) genes, which facilitates xylose metabolism (Xu et al, 2016)
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