Maltotriose utilization in lager yeast strains: MTT1 encodes a maltotriose transporter

Abstract

Maltotriose is the second most abundant fermentable sugar in wort and, due to incomplete fermentation, residual maltotriose in beer causes both quality and economic problems in the brewing industry. To identify genes that might improve utilization of maltotriose, we developed a library containing genomic DNA from four lager strains and a laboratory Saccharomyces cerevisiae strain and isolated transformants that could grow on YP/2% maltotriose in the presence of 3 mg/l of the respiratory inhibitor antimycin A. In this way we found a gene which shared 74% similarity with MPH2 and MPH3, 62% similarity with AGT1 and 91% similarity with MAL61 and MAL31, all encoding known maltose transporters. Moreover, the gene shared an even higher similarity (98%) with the uncharacterized Saccharomyces pastorianus mty1 gene (M. Salema-Oom, unpublished; NCBI Accession No. AJ491328). Therefore, we named the gene MTT1 (mty1-like transporter). We showed that the gene was present in four different lager strains but was absent from the laboratory strain CEN.PK113-7D. The ORF in the plasmid isolated from the library lacks 66 base pairs from the 3 -end of MTT1 but instead contains 54 bp of the vector. We named this ORF MTT1alt (NCBI Accession No. DQ010174).14 C-Maltose and repurified 14 C-maltotriose were used to show that MTT1 and, especially, MTT1alt, encode maltose transporters for which the ratio between activities to maltotriose and maltose is higher than for most known maltose transporters. Introduction of MTT1 or MTT1alt into lager strain A15 raised maltotriose uptake by about 17% or 105%, respectively.

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

“…[U- 14 C]maltose was Amersham CFB182 from GE Healthcare Ltd. (Bucks, United Kingdom). [U- 14 C]maltotriose was ARC627 from American Radiolabeled Chemicals, Inc. (St. Louis, MO), and was repurified before use (6). Nucleotides, enzymes, and antimycin A were from SigmaAldrich (Helsinki, Finland) or Roche (Espoo, Finland).…”

“…The same group has also shown (33) that overexpression of AGT1 on a multicopy plasmid in an industrial yeast strain with a very limited ability to ferment maltotriose provided the strain with increased maltotriose uptake activity and the ability to ferment maltotriose efficiently. In 2005, a novel kind of ␣-glucoside transporter was independently found by two groups (6,30) in some industrial strains of brewer's, baker's, and distiller's yeasts. These transporters are coded by MTT1 (also called MTY1) genes, which are 90 and 54% identical to the MAL31 and AGT1 genes, respectively.…”

Progress in Metabolic Engineering of Saccharomyces cerevisiae

“…Several known transporters carry out maltotriose uptake in S. cerevisiae (67,68). The recently identified MTTI gene encodes another maltotriose transporter, and its overexpression in a lager brewing strain resulted in significantly increased maltotriose uptake (73). Dextrins make up about 25% of the carbohydrates in wort and are usually nonfermentable by industrial Saccharomyces strains.…”

Yeast: World’s Finest Chef

“…This is under similar regulation by the presence of glucose and maltose, therefore most studies have focused in an efficient uptake of this carbohydrate [54]. Those works showed that overexpression of maltotriose transporters lead to positive effects on its metabolism [54,55].…”