12. Self-cloning brewing yeast—New dimension of beer fermentation?
Susann Fischer (1), Thomas Becker (1); (1) Chair of Brewing and Beverage Technology, Technische Universität München, Freising, Germany
Technical Session 3: Yeast Biotechnology
Sunday, August 14 • 9:45–11:30 a.m.
Plaza Building, Concourse Level, Governor’s Square 15
Yeast is the primary microorganism used for fermented beverages such
as beer. However, existing individual strains will not completely
fulfill future demands for an efficient and high-quality fermentation.
In this case, several research groups are focusing on the evaluation of
wild Saccharomyces strains or non-Saccharomyces strains to
enhance fermentation ability under industrial conditions. Another
interesting possibility for targeted optimization of brewing yeast could
be the self-cloning procedure. Self-cloning does not result in a GMO,
due to the usage of homologous nucleic acid sequences. However, to avoid
metabolic burden through constitutive gene expression and translation,
induced gene expression of relevant genes is necessary for industrial
fermentation. Induced gene expression with common inducible expression
systems or equivalent inductors such as galactose and copper are
prohibited for the production of foods and beverages. Therefore,
temperature- and ethanol-induced gene expression under brewing
conditions is the main focus of our research group. The industrial yeast
S. cerevisiae is adapted to different stressors such as a high
concentration of ethanol, osmotic pressure, limitation in nutrition and
temperature shifts. This temperature shift leads to a modification of
specific genetic regulation. The evaluation of 10 different homologue
promoters of the lager yeast TUM 34/70 showed strong expression under
temperature shifts from 12°C to 4°C and weak induction under varied
ethanol concentrations at 12°C of 3 promoters. Further, the steady-state
expression of these stress-relevant promoters is nearly constant during
fermentation. Besides promoter screening, the ability of the evaluated
promoters to enhance the content of volatile metabolites during the
transition from fermentation to maturation under brewing conditions are
the main aspects of this study. Therefore, self-cloning brewing yeast
was created by assembling a homologue gene cassette containing the
evaluated promoter, the target genes ATF1 or GPD1 and the homologous selection marker SMR1. The gene ATF1
encodes for the alcohol-acetyltransferase that is responsible for the
formation of several volatile acetate esters such as ethyl acetate and
isoamyl acetate during fermentation. GPD1 encodes for
glycerol-3-phosphate dehydrogenase and is the key enzyme in glycerol
synthesis. The gene cassette was inserted into the URA3 locus of the
lager yeast TUM 34/70. Fermentations were carried out by use of
synthetic wort (12°P) at 12°C in 2 L EBC tubes. In addition to biomass,
extract decrease and ethanol production volatile metabolites and
glycerol were analyzed. Temperature shift from 12°C to 4°C was carried
out after 144 hr of fermentation and the increase of volatile
metabolites and glycerol was observed during 72 hr.
After graduation from an apprenticeship as a winemaker, Susann
Fischer started the study of enology (Dipl.-Ing. (FH)) at the University
of Applied Science Wiesbaden-Geisenheim (Germany). In 2012 she
graduated from Justus-Liebig University Gießen (Germany) with an M.S.
degree in wine technology, with a focus on the genetic background of
volatile metabolite synthesis of the non-Saccharomyces yeast Hanseniaspora uvarum.
Susann is currently working toward a Ph.D. degree at the Technische
Universität München (Germany), with a research focus on
temperature-induced gene expression systems for self-cloning brewing
yeast.
