Global gene expression analysis of Saccharomyces cerevisiae grown under redox potential‐controlled very‐high‐gravity conditions

Abstract

Redox potential (ORP) plays a pivotal role in yeast viability and ethanol production during very-high-gravity (VHG) ethanol fermentation. In order to identify the correlation between redox potential profiles and gene expression patterns, global gene expression of Saccharomyces cerevisiae was investigated. Results indicated that significant changes in gene expression occurred at the periods of 0 - 6 h and 30 - 36 h, respectively. Changes noted in the period of 0 - 6 h were mainly related to carbohydrate metabolism. In contrast, gene expression variation at 30 - 36 h could be attributed primarily to stress response. Although CDC19 was down-regulated, expression of PYK2, PDC6 and ADH2 correlated inversely with ORP. Meanwhile, expression of GPD1 decreased due to the depletion of dissolved oxygen in the fermentation broth, but expression of GPD2 correlated with ORP. Transcription of genes encoding heat shock proteins was characterized by uphill, downhill, valley and plateau expression profiles, accordingly to specific function in stress response. These results highlight the role of ORP in modulating yeast physiology and metabolism under VHG conditions.

Transcriptional analysis of Kluyveromyces marxianus for ethanol production from inulin using consolidated bioprocessing technology

“…Pyruvate was first converted to acetaldehyde by pyruvate decarboxylase (pdc), which was then reduced to ethanol by alcohol dehydrogenase (adh) in the pathway of ethanol formation. The pyruvate decarboxylase, PDC1 , played a crucial role in the decarboxylation of pyruvate in cells, and the expression of PDC1 in high ethanol concentrations (230-N-72 and 230-130mV-36 against 120-N-24) was enhanced by roughly threefold, which agreed with previous results [ 26 ]. In addition, an appropriate aeration resulted in a slightly higher RPKM value of PDC1 (25,820 vs 22,334).…”

“…The levels of expression (RPKM values) demonstrated the remarkable functions of four ADH genes (Adh1p–Adh4p), which could be classified into two types according to the phylogenetic tree. Adh1p and Adh2p were found to be located in the cytosol, were the main functional alcohol dehydrogenases under anaerobic conditions, and kept a high transcriptional level under very high gravity conditions [ 26 , 30 ], which was in accordance with our results in this article. Additionally, Adh3p and Adh4p were located in the mitochondria.…”

“…Two kinds of pyruvate kinases, Pyk1p and Pyk2p (encoded by CDC19 and PYK2 , respectively), have been observed in S. cerevisiae so far [ 24 , 25 ]. It was indicated previously that the expression of Pyk1p had nothing to do with the accumulation of ethanol [ 26 ], but it might be concerned with glucose utilization under the conditions of high temperature or resistance to environmental stress [ 24 ]. Only one kind of pyruvate kinase was detected in K. marxianus Y179, KmPyk1p, the identity of which was 86% homologous with Pyk1p in S. cerevisiae .…”

Editorial: Biotechnology Journal in Asia – the first official AFOB special issue

“…Two papers under the broad theme of industrial biotechnology are included in this Special Issue. Liu et al [10] investigated correlation between redox potential (ORP) profiles and gene expression pattern of Saccharomyces cerevisiae . Liu et al's results indicate that significant changes in gene expression occurred at the periods of 0–6 h and 30–36 h, respectively, highlighting the role of ORP in modulating yeast physiology and metabolism under very‐high‐gravity ethanol fermentation conditions [10].…”

“…Liu et al [10] investigated correlation between redox potential (ORP) profiles and gene expression pattern of Saccharomyces cerevisiae . Liu et al's results indicate that significant changes in gene expression occurred at the periods of 0–6 h and 30–36 h, respectively, highlighting the role of ORP in modulating yeast physiology and metabolism under very‐high‐gravity ethanol fermentation conditions [10]. Another paper by Lee et al [11] reviews the developments in high‐throughput analysis of the content of microalgae biomass; microalgae being a promising feedstock for biofuels and bio‐based chemical production.…”