fulltext.study @t Gmail

Deletion of the HXK2 gene in Saccharomyces cerevisiae enables mixed sugar fermentation of glucose and galactose in oxygen-limited conditions

Paper ID Volume ID Publish Year Pages File Format Full-Text
34698 45040 2014 7 PDF Available
Title
Deletion of the HXK2 gene in Saccharomyces cerevisiae enables mixed sugar fermentation of glucose and galactose in oxygen-limited conditions
Abstract

•In oxygen-limited conditions, energetic barrier limits metabolic flexibility of S. cerevisiae.•Catabolite repression was alleviated in the S. cerevisiae by deleting the HXK2 gene.•The Δhxk2 strain could prepare mRNAs of GAL genes, and thus the corresponding proteins during glucose consumption period.•The Δhxk2 strain was capable of fermenting glucose and galactose in oxygen-limited conditions.

Galactose is one of the major sugar components of red seaweeds along with glucose. In Saccharomyces cerevisiae, synthesis of galactose-metabolizing enzymes (the Leloir proteins) is under tight and complex regulation in the presence of glucose by a mechanism called catabolite repression. As a result, when both sugars are concurrently present in the medium under oxygen-limited conditions, the yeast cannot utilize galactose even after glucose consumption. Research efforts on mixed sugar fermentation of glucose/galactose, therefore, were made in the presence of oxygen, thereby resulting in sequential substrate consumption, and low ethanol yield and productivity. In this study, mixed sugar fermentation of glucose and galactose in oxygen-limited conditions was achieved by deleting the HXK2 gene, a moonlighting protein acting as hexokinase or repressor involved in catabolite repression of S. cerevisiae. Remarkably, the S. cerevisiae D452-2Δhxk2 strain utilized galactose after glucose depletion without a diauxic lag period, whereas the parental strain could not use galactose at all under oxygen-limited conditions. The Δhxk2 strain fermented galactose at the consumption rate of 3.02 ± 0.10 g/L/h to produce ethanol with a yield of 0.44 ± 0.01 g ethanol/g galactose. Complementation of the Δhxk2 strain with the plasmid-harbored HXK2 gene under the control of various promoters clearly showed that the galactose consumption rates were inversely related to the mRNA levels of the HXK2 gene. The transcription of the GAL genes was dramatically elevated by deleting the HXK2 gene, whereas the expressions of hexokinase genes were not significantly affected. We concluded that the HXK2-deleted strain is able to efficiently utilize both glucose and galactose in the oxygen-limited conditions by alleviating catabolite-repression.

Keywords
Mixed sugar fermentation of glucose and galactose; Catabolite repression; Ethanol; Marine biomass; Saccharomyces cerevisiae
First Page Preview
Deletion of the HXK2 gene in Saccharomyces cerevisiae enables mixed sugar fermentation of glucose and galactose in oxygen-limited conditions
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us
Publisher
Database: Elsevier - ScienceDirect
Journal: Process Biochemistry - Volume 49, Issue 4, April 2014, Pages 547–553
Authors
, , , ,
Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us