Abstract
Approximately 25% of all carbohydrates in industrial worts are poorly, if at all, fermented by brewing yeast. This includes dextrins, β-glucans, arabinose, xylose, disaccharides such as isomaltose, nigerose, kojibiose, and trisaccharides such as panose and isopanose. As the efficient utilization of carbohydrates during the wort’s fermentation impacts the alcohol yield and the organoleptic traits of the product, developing brewing strains with enhanced abilities to ferment subsets of these sugars is highly desirable. In this study, we developed Saccharomyces pastorianus laboratory yeast strains with a superior capacity to grow on isomaltose and panose. First, we designed a plasmid toolbox for the stable integration of genes into lager strains. Next, we used the toolbox to elevate the levels of the α-glucoside transporter Agt1 and the major isomaltase Ima1. This was achieved by integrating synthetic AGT1 and IMA1 genes under the control of strong constitutive promoters into defined genomic sites. As a result, strains carrying both genes showed a superior capacity to grow on panose and isomaltose, indicating that Ima1 and Agt1 act in synergy to consume these sugars. Our study suggests that non-GMO strategies aiming to develop strains with improved isomaltose and panose utilization could include identifying strains that overexpress AGT1 and IMA1.
Highlights
Published: 7 July 2021Lager is the most popular type of beer and represents more than 90% of the total production in the world [1]
This beer type is fermented by strains of the lager yeast, Saccharomyces pastorianus, the origin of which derives from the domesticated allotetraploid interspecies hybrid between Saccharomyces cerevisiae and the cold-tolerant Saccharomyces eubayanus [2,3,4,5]
This study aimed to examine the role of AGT1 and IMA1 in the consumption of sugars, which commonly remain unused during the beer brewing process by lager yeast, by a genetic approach
Summary
Lager is the most popular type of beer and represents more than 90% of the total production in the world [1]. This beer type is fermented by strains of the lager yeast, Saccharomyces pastorianus, the origin of which derives from the domesticated allotetraploid interspecies hybrid between Saccharomyces cerevisiae and the cold-tolerant Saccharomyces eubayanus [2,3,4,5]. The Saaz-type lager strain Unterhefe No 1, later termed Saccharomyces carlsbergensis and S. pastorianus, was the first pure culture of yeast. This strain was isolated by Emil C. Hansen in 1883 [15]
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