title: Maltose and maltotriose utilisation by group I strains of the hybrid lager yeast Saccharomyces pastorianus.
abstract: Brewer's wort is a challenging environment for yeast as it contains predominantly α-glucoside sugars. There exist two subgroups of the lager yeast Saccharomyces pastorianus which differ in sugar utilisation. We performed wort fermentations and compared representative strains from both groups with respect to their ability to transport and ferment maltose and maltotriose. Additionally, we mapped the transporters MALx1, AGT1, MPHx and MTT1 by Southern blotting. Contrary to previous observations, group I comprises a diverse set of strains, with varying ability to transport and ferment maltotriose. Of the eight group I strains, three efficiently utilised maltotriose, a property enabled by the presence of transmembrane transporters SeAGT1 and MTT1 A58, a variant of the group I type strain (CBS1513) performed particularly well, taking up maltotriose at a higher rate than maltose and retaining significant transport activity at temperatures as low as 0°C. Analysis of transporter distribution in this strain revealed an increased copy number of the MTT1 gene, which encodes the only permease known with higher affinity for maltotriose than maltose and low temperature dependence for transport. We propose that much of the variation in lager yeast fermentation behaviour is determined by the presence or absence of specific transmembrane transporters.
authors.affiliation: VTT Technical Research Centre of Finland Ltd, Tietotie 2, PO Box 1000, FI-02044 VTT, Espoo, Finland Department of Biotechnology and Chemical Technology, Aalto University, School of Chemical Technology, Kemistintie 1, PO Box 16100, FI-00076 Aalto, Espoo, Finland frederico.magalhaes@vtt.fi.
authors.forename: Frederico
authors.initials: F
authors.lastname: Magalhães
authors.affiliation: VTT Technical Research Centre of Finland Ltd, Tietotie 2, PO Box 1000, FI-02044 VTT, Espoo, Finland.
authors.forename: Virve
authors.initials: V
authors.lastname: Vidgren
authors.affiliation: VTT Technical Research Centre of Finland Ltd, Tietotie 2, PO Box 1000, FI-02044 VTT, Espoo, Finland.
authors.forename: Laura
authors.initials: L
authors.lastname: Ruohonen
authors.affiliation: VTT Technical Research Centre of Finland Ltd, Tietotie 2, PO Box 1000, FI-02044 VTT, Espoo, Finland.
authors.forename: Brian
authors.initials: B
authors.lastname: Gibson
mesh_terms: D015139:Blotting, Southern; D002874:Chromosome Mapping; D005285:Fermentation; D018628:Gene Dosage; D008320:Maltose / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics; D012440:Saccharomyces / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D014312:Trisaccharides / Q000378:metabolism*
chemical_list: D026901:Membrane Transport Proteins; D014312:Trisaccharides; C008317:maltotriose; D008320:Maltose
keywords: Group I; MTT1; hybrid; lager; maltotriose; α-glucoside transporters