Accumulation of intracellular S-adenosylmethionine increases the fermentation rate of bottom-fermenting brewer's yeast during high-gravity brewing

Abstract

High-gravity brewing has been used to reduce costs and energy, as well as to produce new types of beer with high alcohol content. To identify the key metabolic pathways underlying efficient high-gravity brewing, we explored metabolites that were highly accumulated during alcoholic fermentation under high-maltose conditions using bottom-fermenting brewer's yeast, Saccharomyces pastorianus. Based on metabolomic data, we focused on S-adenosylmethionine (SAM), which may be involved in glycolysis and alcoholic fermentation in the closely related yeast species Saccharomyces cerevisiae. Exogenous SAM led to an increase in fermentation rate in both high-maltose synthetic medium and high-gravity wort. Although SAM is composed of methionine and the adenosine moiety of ATP, neither methionine nor adenosine significantly increased the fermentation rate. These results suggest that SAM is specifically associated with the fermentation rate of bottom-fermenting brewer's yeast. Deletion of the adenosine kinase gene ADO1, which leads to an accumulation of SAM in S.cerevisiae cells, elevated the fermentation rate in high-glucose synthetic medium at 15°C; however, this ado1Δ effect became less significant at higher temperatures. Similarly, a SAM-accumulating S.pastorianus mutant strain, with enhanced resistance to the adenosine analog cordycepin, exhibited a higher fermentation rate in both high-maltose synthetic medium and high-gravity wort. Taken together, our study demonstrates that SAM acts as a positive regulator in high-gravity brewing at low temperatures and that cordycepin resistance could serve as a useful indicator for breeding S.pastorianus strains with high fermentation performance.