Maltotriose fermentation by Saccharomyces cerevisiae

Abstract

Maltotriose, the second most abundant sugar of brewer's wort, is not fermented but is respired by several industrial yeast strains. We have isolated a strain capable of growing on a medium containing maltotriose and the respiratory inhibitor, antimycin A. This strain produced equivalent amounts of ethanol from 20 g l(-1) glucose, maltose, or maltotriose. We performed a detailed analysis of the rates of active transport and intracellular hydrolysis of maltotriose by this strain, and by a strain that does not ferment this sugar. The kinetics of sugar hydrolysis by both strains was similar, and our results also indicated that yeast cells do not synthesize a maltotriose-specific alpha-glucosidase. However, when considering active sugar transport, a different pattern was observed. The maltotriose-fermenting strain showed the same rate of active maltose or maltotriose transport, while the strain that could not ferment maltotriose showed a lower rate of maltotriose transport when compared with the rates of active maltose transport. Thus, our results revealed that transport across the plasma membrane, and not intracellular hydrolysis, is the rate-limiting step for the fermentation of maltotriose by these Saccharomyces cerevisiae cells.

Specific Imaging of Bacterial Infection Using 6″-18F-Fluoromaltotriose: A Second-Generation PET Tracer Targeting the Maltodextrin Transporter in Bacteria

“…This difference in metabolism could also permit the 6$-18 F-fluoromaltotriose to discriminate between bacterial and fungal infections. There is evidence that, although fungi can take up and metabolize maltose, maltotriose appears unique in that it is metabolized more slowly in yeast (25). More experiments with bacteria bearing mutations in the maltodextrin transporter are needed to truly understand the mechanism of uptake and use of the tracer.…”

Improved Fermentation Performance of a Lager Yeast after Repair of Its AGT1 Maltose and Maltotriose Transporter Genes

“…The selection strategy (growth of glucose-repressed cells on maltotriose in the presence of the respiratory inhibitor antimycin A) was exceptionally effective; e.g., all 36 selected clones that were tested contained a PGK1 promoter between the promoter and ORF of the AGT1 gene. Both lager and baker's yeast strains have difficulty adapting from growth on glucose to growth on maltotriose when respiration is inhibited (20,40), and for strain A15 this difficulty seems to be greater than for some other lager strains (6). In principle, the integration cassettes used to transform lager strain A15 should work in the same way with other lager strains, since all of the lager strains studied contain the same premature stop codon in the ORFs of their AGT1 genes (36,37) and both of the lager strains studied have identical AGT1 promoter sequences (V. Vidgren, M. Kankainen, J. Londesborough, and L. Ruohonen, unpublished results).…”

Molecular Analysis of Maltotriose Active Transport and Fermentation by Saccharomyces cerevisiae Reveals a Determinant Role for the AGT1 Permease

“…Several studies on sugar utilization by yeast cells have also revealed that maltose and maltotriose are transported by different permeases, while the intracellular maltases are capable of hydrolyzing both sugars (37,42). All yeast ␣-glucoside transport systems so far characterized are H ϩ symporters that use the electrochemical proton gradient to actively transport these sugars into the cell, even for downhill transport (7,30,36).…”