Intracellular Redox Perturbation in Saccharomyces cerevisiae Improved Furfural Tolerance and Enhanced Cellulosic Bioethanol Production.

Chen-Guang Liu,Feng-Wu Bai,Xin-Qing Zhao,Ke-Yi Li,Muhammad Aamer Mehmood,Kai Li,Chularat Sakdaronnarong

doi:10.3389/fbioe.2020.00615

Abstract

Furfural is a major toxic byproduct found in the hydrolysate of lignocellulosic biomass, which adversely interferes with the growth and ethanol fermentation of Saccharomyces cerevisiae. The current study was focused on the impact of cofactor availability derived intracellular redox perturbation on furfural tolerance. Here, three strategies were employed in cofactor conversion in S. cerevisiae: (1) heterologous expression of NADH dehydrogenase (NDH) from E. coli which catalyzed the NADH to NAD+ and increased the cellular sensitivity to furfural, (2) overexpression of GLR1, OYE2, ZWF1, and IDP1 genes responsible for the interconversion of NADPH and NADP+, which enhanced the furfural tolerance, (3) expression of NAD(P)+ transhydrogenase (PNTB) and NAD+ kinase (POS5) which showed a little impact on furfural tolerance. Besides, a substantial redistribution of metabolic fluxes was also observed with the expression of cofactor-related genes. These results indicated that NADPH-based intracellular redox perturbation plays a key role in furfural tolerance, which suggested single-gene manipulation as an effective strategy for enhancing tolerance and subsequently achieving higher ethanol titer using lignocellulosic hydrolysate.

Highlights

Bioethanol is considered as one of the most promising liquid alternatives to fossil fuels, which can be either blended with gasoline or can directly be used as fuel in dedicated engines (Kuhad et al, 2016; Xu and Lin, 2018)
It was found that the strain expressing NADH dehydrogenase (BYNDH) had the best cell growth when compared to wild type and other mutants because the NADH dehydrogenase might have enhanced the respiratory flux of the strain
It was shown that after the heterologous expression of NDH gene, the strain became extremely sensitive to furfural and was unable grow in medium containing 4 g/L of furfural, while the strain overexpressing Formate dehydrogenase (FDH) gene had similar growth when compared to the wild type due to lack of formate as a substrate

Summary

Introduction

Bioethanol is considered as one of the most promising liquid alternatives to fossil fuels, which can be either blended with gasoline or can directly be used as fuel in dedicated engines (Kuhad et al, 2016; Xu and Lin, 2018). The first-generation (1G) ethanol is being produced predominately from starch-based feedstocks. Despite its potential, it cannot be produced from the food-crops-based sugars due to the enormous demands of food supply for the increasing population. The production of cellulosic ethanol from lignocellulosic biomass “2G fuel ethanol” has attracted significant attention. There are several bottlenecks in the biological transformation of cellulosic biomass to fuel ethanol which includes tedious pretreatments, pretreatment-derived toxic compounds, and inefficient enzymatic hydrolysis. It is required to develop robust strains to achieve the economic efficiency of 2G fuel production. The presence of toxic by-products produced during the pretreatment of lignocellulosic biomass is a

Methods

Results

Conclusion