Hydrogen sulphide production by bottom-fermenting yeast is related to nitrogen starvation signalling

Bottom-fermenting yeast subjected to nitrogen starvation during exponential growth were found to produce hydrogen sulphide. In order to investigate a possible relationship between nitrogen starvation and hydrogen sulphide production, bottom-fermenting yeast strains, with depressed nitrogen starvation responses, were constructed by disrupting GLN3 and GAT1, encoding transcription factors that activate the transcription of NCR (nitrogen catabolite repression)-sensitive genes. In order to construct additional bottom-fermenting yeast strains with depressed nitrogen starvation responses, DAL80-, GZF3- and URE2-overexpressing strains were also constructed as these genes are also involved in NCR, and repress transcription of NCR-sensitive genes. Bottom-fermenting yeast have two types of genes, those derived from Saccharomyces cerevisiae-type and S. bayanus-type genomes. Both types of genes were disrupted/overexpressed in the constructed strains. In wort fermentations, all of the constructed strains produced less hydrogen sulphide and less of the thiol off-flavour compounds, 3-methyl-2-butene-1-thiol and 2-mercapto-3-methyl-1-butanol than the parent strains. Copyright (C) 2013 The Institute of Brewing & Distilling