Differences in Formation Mechanisms of Phenolic Off-Flavor Compounds among Yeast Species

Phenolic off-flavor compounds such as 4-vinylguaiacol (4-VG) affect the quality of fermented foods. In Saccharomyces cerevisiae, 4-VG production requires prenylated FMN (flavin mononucleotide) produced by the mitochondrial protein Pad1. To examine this mechanism further, we expressed Escherichia coli ubiX, whose gene product prenylates FMN in E. coli, in an S. cerevisiae Delta pad1 strain, which recovered the ability to produce 4-VG. Because E. coli UbiX is expected to localize to the cytoplasm in the transformed yeast, next, we expressed a truncated Pad1 (tPad1) variant lacking the mitochondrial translocation signal sequence in S. cerevisiae Delta pad1. The transformed strain also recovered the ability to produce 4-VG; furthermore, it produced a larger amount of 4-VG than wild-type S. cerevisiae, indicating that 4-VG production in S. cerevisiae may be mediated by the partial mislocalization of Pad1 to the cytoplasm. We also expressed the gene encoding Dekkera (Brettanomyces) bruxellensis phenolic acid decarboxylase (DbPAD) in S. cerevisiae Delta pad1. The transformed yeast recovered the ability to produce 4-VG, indicating that the D. bruxellensis phenolic acid decarboxylation reaction does not require prenylated FMN. Sequencing of the cloned DbPAD gene showed that the translation start codon differs from previous reports; therefore, we recloned the DbPAD gene from the position predicted to be the translation initiation point (designated DbPADs). Transformation of S. cerevisiae Delta pad1 with DbPADs further increased the amount of 4-VG produced. Collectively, these findings provide insight into the mechanism of off-flavor production by different yeast species.

Automated summary

Phenolic off-flavor compounds, like 4-vinylguaiacol (4-VG), have a negative impact on the quality of fermented foods. This study investigated the production of 4-VG in Saccharomyces cerevisiae and found that it requires prenylated FMN produced by the mitochondrial protein Pad1. Expressing Escherichia coli ubiX, which prenylates FMN in E. coli, in a S. cerevisiae Delta pad1 strain restored the ability to produce 4-VG. The findings suggest that the mislocalization of Pad1 to the cytoplasm may play a role in 4-VG production.