A deletion in theSTA1promoter determines maltotriose and starch utilization inSTA1+Saccharomyces cerevisiaestrains

Abstract

AbstractDiastatic strains ofSaccharomyces cerevisiaeare common contaminants in beer fermentations and are capable of producing an extracellularSTA1-encoded glucoamylase. Recent studies have revealed variable diastatic ability in strains tested positive forSTA1,and here we elucidate genetic determinants behind this variation. We show that poorly diastatic strains have a 1162 bp deletion in the promoter ofSTA1. With CRISPR/Cas9-aided reverse engineering, we show that this deletion greatly decreases the ability to grow in beer and consume dextrin, and the expression ofSTA1. New PCR primers were designed for differentiation of highly and poorly diastatic strains based on the presence of the deletion in theSTA1promoter. In addition, using publically available whole genome sequence data, we show that theSTA1gene is prevalent in among the ‘Beer 2’/’Mosaic Beer’ brewing strains. These strains utilize maltotriose efficiently, but the mechanisms for this have been unknown. By deletingSTA1from a number of highly diastatic strains, we show here that extracellular hydrolysis of maltotriose throughSTA1appears to be the dominant mechanism enabling maltotriose use during wort fermentation inSTA1+strains. The formation and retention ofSTA1seems to be an alternative evolutionary strategy for efficient utilization of sugars present in brewer’s wort. The results of this study allow for the improved reliability of molecular detection methods for diastatic contaminants in beer, and can be exploited for strain development where maltotriose use is desired.