Transcription analysis of recombinant industrial and laboratory Saccharomyces cerevisiae strains reveals the molecular basis for fermentation of glucose and xylose

Akinori Matsushika,Tamotsu Hoshino,Tetsuya Goshima

doi:10.1186/1475-2859-13-16

Abstract

BackgroundThere has been much research on the bioconversion of xylose found in lignocellulosic biomass to ethanol by genetically engineered Saccharomyces cerevisiae. However, the rate of ethanol production from xylose in these xylose-utilizing yeast strains is quite low compared to their glucose fermentation. In this study, two diploid xylose-utilizing S. cerevisiae strains, the industrial strain MA-R4 and the laboratory strain MA-B4, were employed to investigate the differences between anaerobic fermentation of xylose and glucose, and general differences between recombinant yeast strains, through genome-wide transcription analysis.ResultsIn MA-R4, many genes related to ergosterol biosynthesis were expressed more highly with glucose than with xylose. Additionally, these ergosterol-related genes had higher transcript levels in MA-R4 than in MA-B4 during glucose fermentation. During xylose fermentation, several genes related to central metabolic pathways that typically increase during growth on non-fermentable carbon sources were expressed at higher levels in both strains. Xylose did not fully repress the genes encoding enzymes of the tricarboxylic acid and respiratory pathways, even under anaerobic conditions. In addition, several genes involved in spore wall metabolism and the uptake of ammonium, which are closely related to the starvation response, and many stress-responsive genes mediated by Msn2/4p, as well as trehalose synthase genes, increased in expression when fermenting with xylose, irrespective of the yeast strain. We further observed that transcript levels of genes involved in xylose metabolism, membrane transport functions, and ATP synthesis were higher in MA-R4 than in MA-B4 when strains were fermented with glucose or xylose.ConclusionsOur transcriptomic approach revealed the molecular events underlying the response to xylose or glucose and differences between MA-R4 and MA-B4. Xylose-utilizing S. cerevisiae strains may recognize xylose as a non-fermentable carbon source, which induces a starvation response and adaptation to oxidative stress, resulting in the increased expression of stress-response genes.

Highlights

There has been much research on the bioconversion of xylose found in lignocellulosic biomass to ethanol by genetically engineered Saccharomyces cerevisiae
(industrial and laboratory strains) on ethanol fermentation, fermentation by the recombinant S. cerevisiae strains MAR4 and MA-B4 was performed anaerobically in yeast peptone (YP)-based media supplied with 40 g/L glucose (YPD medium) and 40 g/L xylose (YPX medium) in which aureobasidin A was not included
When xylose was provided as the sole carbon source, MA-R4 grew at a higher growth rate than MA-B4, with growth rates of 0.031 ± 0.001 h-1 for MA-R4 and 0.020 ± 0.001 h-1 for MA-B4

Summary

Introduction

There has been much research on the bioconversion of xylose found in lignocellulosic biomass to ethanol by genetically engineered Saccharomyces cerevisiae. The rate of ethanol production from xylose in these xylose-utilizing yeast strains is quite low compared to their glucose fermentation. Two diploid xylose-utilizing S. cerevisiae strains, the industrial strain MA-R4 and the laboratory strain MA-B4, were employed to investigate the differences between anaerobic fermentation of xylose and glucose, and general differences between recombinant yeast strains, through genome-wide transcription analysis. The yeast Saccharomyces cerevisiae is the preferred organism for industrial ethanol production from sugar derived from starch and sucrose due to its high growth rate, rapid fermentation rate, and high ethanol productivity under anaerobic conditions, together with high tolerance for ethanol and low pH. Zhou et al [17] recently reported that combining metabolic and evolutionary engineering generates new XIexpressing strains of S. cerevisiae with a greatly improved anaerobic growth rate (0.203 h-1), xylose conversion rate (1.866 g g-1 h-1), and ethanol yield (0.41 g/g)

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