Maltose and maltotriose transport into ale and lager brewer´s yeast strains

Dissertation VTT PUBLICATIONS 748 Virve Vidgren Maltose and maltotriose transport into ale and lager brewer´s yeast strains VTT PUBLICATIONS 748 Maltose and maltotriose transport into ale and lager brewer´s yeast strains Virve Vidgren Division of Genetics Department of Biosciences Faculty of Biological and Environmental Sciences University of Helsinki, Finland A dissertation for the degree of Doctor of Philosophy to be presented, by permission of the Faculty of Biological and Environmental Sciences, the University of Helsinki, for public examination and debate in Auditorium XV at the University of Helsinki, Main Building, Unioninkatu 34, on the 10th of December 2010, at 12 o’clock noon. ISBN 978-951-38-7415-5 (soft back ed.) ISSN 1235-0621 (soft back ed.) ISBN 978-951-38-7416-2 (URL: http://www.vtt.fi/publications/index.jsp) ISSN 1455-0849 (URL: http://www.vtt.fi/publications/index.jsp) Copyright © VTT 2010 JULKAISIJA – UTGIVARE – PUBLISHER VTT, Vuorimiehentie 5, PL 1000, 02044 VTT puh. vaihde 020 722 111, faksi 020 722 4374 VTT, Bergsmansvägen 5, PB 1000, 02044 VTT tel. växel 020 722 111, fax 020 722 4374 VTT Technical Research Centre of Finland, Vuorimiehentie 5, P.O. Box 1000, FI-02044 VTT, Finland phone internat. +358 20 722 111, fax + 358 20 722 4374 Technical editing Mirjami Pullinen Text formatting Raija Sahlstedt Edita Prima Oy, Helsinki 2010 Virve Vidgren. Maltose and maltotriose transport into ale and lager brewer´s yeast strains. Espoo 2010. VTT Publications 748. 93 p. + app. 65 p. Keywords brewer’s yeast strains, high-gravity brewing, -glucoside transporters, maltose uptake, maltotriose uptake, MAL genes, MPHx, AGT1, MTT1, temperature-dependence of transport, AGT1 promoter, MAL-activator, Mig1 Abstract Maltose and maltotriose are the two most abundant sugars in brewer’s wort, and thus brewer’s yeast’s ability to utilize them efficiently is of major importance in the brewing process. The increasing tendency to utilize high and very-high-gravity worts containing increased concentrations of maltose and maltotriose renders the need for efficient transport of these sugars even more pronounced. Residual maltose and maltotriose are quite often present especially after high and very-high-gravity fermentations. Sugar uptake capacity has been shown to be the rate-limiting factor for maltose and maltotriose utilization. The aim of the present study was to find novel ways to improve maltose and maltotriose utiliza-tion during the main fermentation. Maltose and maltotriose uptake characteristics of several ale and lager strains were studied. Genotype determination of the genes needed for maltose and mal-totriose utilization was performed. Gene expression and maltose uptake inhibi-tion studies were carried out to reveal the dominant transporter types actually functioning in each of the strains. Temperature-dependence of maltose transport was studied for ale and for lager strains as well as for each of the single sugar transporter proteins Agt1p, Malx1p and Mtt1p. The AGT1 promoter regions of one ale and two lager strains were sequenced by chromosome walking and the promoter elements were searched for using computational methods. The results showed that ale and lager strains predominantly use different mal-tose and maltotriose transporter types for maltose and maltotriose uptake. Agt1 transporter was found to be the dominant maltose/maltotriose transporter in the ale strains whereas Malx1 and Mtt1-type transporters dominated in the lager strains. All lager strains studied were found to possess an AGT1 gene encoding a truncated polypeptide unable to function as maltose transporter. The ale strains 3 ... - tailieumienphi.vn