ABSTRACT: Beer brewing is a well-known process that still faces great challenges, such as the total consumption of sugars present in the fermentation media. Lager-style beer, major worldwide beer type, is elaborated by Saccharomyces pastorianus (Sp) yeast which must ferment high maltotriose content worts, but its consumption represents a notable problem, especially among Sp strains belonging to group I. Factors like fermentation conditions, presence of maltotriose transporters, transporter copy number variation, and genetic regulation variations contribute to this issue. We assess the factors affecting fermentation in two Sp yeast strains: SpIB1, with limited maltotriose uptake, and SpIB2, known for efficient maltotriose transport. Here, SpIB2 transported significantly more maltose (28%) and maltotriose (32%) compared to SpIB1. Furthermore, SpIB2 expressed all MAL transporters (ScMALx1, SeMALx1, ScAGT1, SeAGT1, MTT1, and MPHx) on the first day of fermentation, while SpIB1 only exhibited ScMalx1, ScAGT1, and MPH2/3 genes. Some SpIB2 transporters had polymorphic transmembrane domains (TMD) resembling MTT1, accompanied by higher expression of these transporters and its positive regulator genes like MAL63. These findings suggest that, in addition of the factors mentioned above, positive regulators of Mal transporters contribute significatively to phenotypic diversity in maltose and maltotriose consumption among the studied lager yeast strains.
