The transcription factors Hsf1 and Msn2 of thermotolerant Kluyveromyces marxianus promote cell growth and ethanol fermentation of Saccharomyces cerevisiae at high temperatures

Abstract

BackgroundHigh temperature inhibits cell growth and ethanol fermentation of Saccharomyces cerevisiae. As a complex phenotype, thermotolerance usually involves synergistic actions of many genes, thereby being difficult to engineer. The overexpression of either endogenous or exogenous stress-related transcription factor genes in yeasts was found to be able to improve relevant stress tolerance of the hosts.ResultsTo increase ethanol yield of high-temperature fermentation, we constructed a series of strains of S. cerevisiae by expressing 8 transcription factor genes from S. cerevisiae and 7 transcription factor genes from thermotolerant K. marxianus in S. cerevisiae. The results of growth curve measurements and spotting test show that KmHsf1 and KmMsn2 can enhance cell growth of S. cerevisiae at 40–42 °C. According to the results of batch fermentation at 43 °C with an initial glucose concentration of 104.8 g/l, the fermentation broths of KmHSF1 and KmMSN2-expressing strains could reach final ethanol concentrations of 27.2 ± 1.4 and 27.6 ± 1.2 g/l, respectively, while the control strain just produced 18.9 ± 0.3 g/l ethanol. Transcriptomic analysis found that the expression of KmHSF1 and KmMSN2 resulted in 55 (including 31 up-regulated and 24 down-regulated) and 50 (including 32 up-regulated and 18 down-regulated) genes with different expression levels, respectively (padj < 0.05). The results of transcriptomic analysis also reveal that KmHsf1 might increase ethanol production by regulating genes related to transporter activity to limit excessive ATP consumption and promote the uptake of glucose; while KmMsn2 might promote ethanol fermentation by regulating genes associated with glucose metabolic process and glycolysis/gluconeogenesis. In addition, KmMsn2 might also help to cope with high temperature by regulating genes associated with lipid metabolism to change the membrane fluidity.ConclusionsThe transcription factors KmHsf1 and KmMsn2 of thermotolerant K. marxianus can promote both cell growth and ethanol fermentation of S. cerevisiae at high temperatures. Different mechanisms of KmHsf1 and KmMsn2 in promoting high-temperature ethanol fermentation of S. cerevisiae were revealed by transcriptomic analysis.Electronic supplementary materialThe online version of this article (10.1186/s13068-017-0984-9) contains supplementary material, which is available to authorized users.

Transcriptomic analysis of thermotolerant yeastKluyveromyces marxianusin multiple inhibitors tolerance

“…86,87 We speculate that the function of MSN2 in K. marxianus might not relate to the inhibitors tolerance or phosphorylation of MSN2 was more important in regulating the genes in response to the multiple inhibitors stress.…”

CRISPR/Cas‐based screening of a gene activation library in Saccharomyces cerevisiae identifies a crucial role of OLE1 in thermotolerance

“…In our previous study, we have found that heterologous expression of K. marxianus HSF1 and MSN2 (denoted as KmHSF1 and KmMSN2 , respectively) in S. cerevisiae promoted cell growth and ethanol fermentation at high temperatures (Li et al ., ). RNA‐Seq‐based transcriptomic analysis revealed that heterologous expression of KmHSF1 and KmMSN2 in S. cerevisiae resulted in 31 and 32 up‐regulated genes, respectively (Fold change > 2, P adj < 0.05).…”

“…Even though the fold change of OLE1 up‐regulation was relatively low, OLE1 ‐overexpressing strain could be enriched after high‐temperature screening, indicating that this level of up‐regulation was sufficient to cause phenotype change. Given that OLE1 was up‐regulated by 1.65‐fold in the strain overexpressing KmMSN2 based on the RNA‐Seq results in our previous study (Li et al ., ), the activation of OLE1 based on the dCas9‐VP64 fusion and g OLE1 _1 in this study is comparable to that by KmMSN2 .…”

“…High temperature seriously destroys cytoskeletal integrity, causes cell morphological abnormalities, inhibits cell division and growth, and impacts metabolic activity (Torija et al ., ; Guyot et al ., ). Great efforts have been made in order to understand the mechanism of yeast thermotolerance and improve it (Caspeta et al ., ,b, ; Shui et al ., ; Jia et al ., ; Li et al ., ). Nevertheless, yeast thermotolerance is a complex phenotype, involving synergistic actions of many genes and thereby being difficult to engineer (Santos and Stephanopoulos, ).…”

“…Biofuels such as bioethanol are becoming increasingly important due to their ability to reduce fossil fuel consumption and reduce greenhouse gas and pollutant emissions (Goldemberg, 2007;Salvo et al, 2017). Large-scale biofuel production benefits greatly from hightemperature fermentation (≥ 40°C) which significantly reduces cooling costs and helps prevent contamination (Abdel-Banat et al, 2010;Li et al, 2017). High operating temperature also benefits a simultaneous saccharification and fermentation (SSF) process because the optimal temperature for enzymes that catalyse the saccharification of biomass is usually over 50°C (Li et al, 2013;Caspeta et al, 2014a,b).…”