Abstract

For maltose fermentation, budding yeast Saccharomyces cerevisiae operates a mechanism that involves transporters (MALT), maltases (MALS) and regulators (MALR) collectively known as MAL genes. However, functional relevance of MAL genes during sake brewing process remains largely elusive, since sake yeast is cultured under glucose-rich condition achieved by the co-culture partner Aspergillus spp.. Here we isolated an ethyl methane sulfonate (EMS)-mutagenized sake yeast strain exhibiting enhanced maltose fermentation compared to the parental strain. The mutant carried a single nucleotide insertion that leads to the extension of the C-terminal region of a previously uncharacterized MALR gene YPR196W-2, which was renamed as MAL73. Introduction of the mutant allele MAL73L with extended C-terminal region into the parental or other sake yeast strains enhanced the growth rate when fed with maltose as the sole carbon source. In contrast, disruption of endogenous MAL73 in the sake yeasts decreased the maltose fermentation ability of sake yeast, confirming that the original MAL73 functions as a MALR. Importantly, the MAL73L-expressing strain fermented more maltose in practical condition compared to the parental strain during sake brewing process. Our data show that MAL73(L) is a novel MALR gene that regulates maltose fermentation, and has been functionally attenuated in sake yeast by single nucleotide deletion during breeding history. Since the MAL73L-expressing strain showed enhanced ability of maltose fermentation, MAL73L might also be a valuable tool for enhancing maltose fermentation in yeast in general.

Highlights

  • Yeast alters its gene expression pattern in response to environmental nutritional conditions, notably including sugar and nitrogen sources

  • These results indicated that K1801M ypr196w-2Δ still had a weak maltose fermentation ability that is dependent upon the mitochondrial electron transfer system, suggesting that another functional MALR that is present in K1801 provides this very weak MALR activity

  • This single nucleotide deletion presumably occurred in the ancestral strain during differentiation and selection for sake fermentation; the resulting truncated form of Ypr196W-2p is apparently hypomorphic, resulting in decreased maltose fermentation ability

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Summary

Introduction

Yeast alters its gene expression pattern in response to environmental nutritional conditions, notably including sugar and nitrogen sources. Alteration of gene expression in response to environmental sugar availability has been extensively studied using the budding yeast Saccharomyces cerevisiae [1]. Maltose, which is a α-disaccharide comprising two α-. A novel regulator of maltose fermentation in sake brewing yeast to publish, or preparation of the manuscript. No additional external funding received for this study

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