MAL73, a novel regulator of maltose fermentation, is functionally impaired by single nucleotide polymorphism in sake brewing yeast

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.

Technological characterisation and probiotic traits of yeasts isolated from Sha'a, a Cameroonian maize-based traditional fermented beverage

“…The ability to assimilate maltose can be lost when yeasts are regularly grown in a glucose-rich medium, inducing repression of genes involved in maltose transport and hydrolysis so that when inoculated into a maltose-rich medium; thus unable to grow ( Kuthan et al., 2003 ). Yeasts with this ability are highly present in cereal-based fermented beverages ( Canonico et al., 2014 ); but some may lose their ability to metabolise maltose completely during evolution or selection ( Ohdate et al., 2018 ).…”

Performance of wild Saccharomyces and Non‐Saccharomyces yeasts as starter cultures in dough fermentation and bread making

“…In some yeast strains, maltose fermentation can be impaired or completely lost due to the mutations that occurred, either from evolution or via the selection and domestication process (Ohdate et al ., 2018). Industrial strains have a higher capacity of maltose utilisation than wild strains because few substrates are rich in maltose in natural environments, and this trait is not heavily selected.…”

Targeted Mutations Produce Divergent Characteristics in Pedigreed Sake Yeast Strains

“…Genetic features such as aneuploidy and loss of heterozygosity are frequently observed in sake yeast. There are many genes specific to sake yeast such as AWA1 [ 4 ] and MAL73 [ 5 ]. However, a detailed examination of genetic sequences [ 3 ] and phenotypes [ 6 , 7 ] revealed the diversity of sake yeasts.…”