Amino Acid Uptake and Yeast Gene Transcription during Industrial Brewery Fermentation

Abstract

Amino acid utilization by yeast during brewer's wort fermentation influences both the fermentation performance and flavor profile of the finished product. To better understand the relationship between the yeast cell and wort amino acid composition, oligonucleotide microarrays were employed to measure the changes in transcription of genes associated with amino acid uptake and utilization during industrial-scale fermentation. Amino acid permeases with narrow specificity for amino acids had the lowest transcription values at the beginning of fermentation (when amino acids were replete), suggesting nitrogen catabolite repression, whereas relatively high transcription at the beginning of fermentation was confined to genes encoding permeases with broad substrate specificity. Nine genes involved in amino acid catabolism demonstrated significant changes in transcription, with most having the highest activity at 60 hr. Exceptions were PUT1, encoding proline oxidase, and CHA1, encoding L-serine deaminase, both with peak transcription at the beginning of fermentation. The only gene demonstrating increased activity in the final stages of fermentation was the threonine aldolase-encoding gene GLY1—a result that could explain the atypical low uptake of threonine. The majority of genes involved in amino acid biosynthesis had maximal expression at low amino acid concentrations, with notable exceptions being genes involved in central nitrogen metabolism and synthesis of glutamine (GLN1 and LYS9) and glutamate (GDH1)—a result that was consistent with the early depletion of glutamine from the wort and supported by the fact that these genes are regulated by nitrogen catabolite response-related transcription factors.