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Extracellular maltotriose hydrolysis by Saccharomyces cerevisiae cells lacking the AGT 1 permease
Author(s) -
Alves S.L.,
Thevelein J.M.,
Stambuk B.U.
Publication year - 2018
Publication title -
letters in applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.698
H-Index - 110
eISSN - 1472-765X
pISSN - 0266-8254
DOI - 10.1111/lam.13048
Subject(s) - maltotriose , maltose , yeast , biology , biochemistry , saccharomyces cerevisiae , permease , fermentation , extracellular , lactose permease , transporter , gene , enzyme
In brewing, maltotriose is the least preferred sugar for uptake by Saccharomyces cerevisiae cells. Although the AGT 1 permease is required for efficient maltotriose fermentation, we have described a new phenotype in some agt1 Δ strains of which the cells do not grow on maltotriose during the first 3–4 days of incubation, but after that, they start to grow on the sugar aerobically. Aiming to characterize this new phenotype, we performed microarray gene expression analysis which indicated upregulation of high‐affinity glucose transporters ( HXT 4 , HXT 6 and HXT 7 ) and α ‐glucosidases ( MAL 12 and IMA 5 ) during this delayed cellular growth. Since these results suggested that this phenotype might be due to extracellular hydrolysis of maltotriose, we attempted to detect glucose in the media during growth. When an hxt ‐null agt1 Δ strain was grown on maltotriose, it also showed the delayed growth on this carbon source, and glucose accumulated in the medium during maltotriose consumption. Considering that the poorly characterized α ‐glucosidase encoded by IMA 5 was among the overexpressed genes, we deleted this gene from an agt1 Δ strain that showed delayed growth on maltotriose. The ima5 Δ agt1 Δ strain showed no maltotriose utilization even after 200 h of incubation, suggesting that IMA 5 is likely responsible for the extracellular maltotriose hydrolysis. Significance and Impact of the Study Maltotriose is the second most abundant sugar present in brewing. However, many yeast strains have difficulties to consume maltotriose, mainly because of its low uptake rate by the yeast cells when compared to glucose and maltose uptake. The AGT 1 permease is required for efficient maltotriose fermentation, but some strains deleted in this gene are still able to grow on maltotriose after an extensive lag phase. This manuscript shows that such delayed growth on maltotriose is a consequence of extracellular hydrolysis of the sugar. Our results also indicate that the IMA 5 ‐encoded α ‐glucosidase is likely the enzyme responsible for this phenotype.