Mutation and deletion of PAD1 and/or FDC1 and absence of phenolic off-flavor production in top- and bottom-fermenting yeasts

To convert ferric acid into 4-vinylguaiacol, Saccharomyces cerevisiae must have intact PAD1 and FDC1 genes. British-type top-fermenting yeast strains have nonsense mutations in both of these genes, whereas bottom-fermenting yeast strains have a nonsense mutation in their S. cerevisiae-type FDC1, and have lost their S. eubayanus-type FDC1 and PAD1 genes. Here top-fermenting yeast transformants in which wild-type PAD1 and FDC1, which were derived from the laboratory yeast S. cereviciae S288C, were inserted in the genome DNA exhibited ferulic aced decarboxylation activity. Similarly, bottom fermenting yeast transform ants expressing wild-type S. cerevisiae-type FDC1 for S. eubayanus-type FDC1 also exhibited ferulic acid decarboxylation activity. Thus, the lack of ferulic acid decarboxylation activity in bottom-fermenting yeast is due to mutation of the S. cerevisiae-type FDC1 gene, coupled with the absence of the S.eubayanus-type FDC1 gene.