Technical Session 22: Yeast IV Session
Brian Gibson, VTT, Espoo, Finland
Co-author(s): Virve Vidgren, VTT, Espoo, Finland; Jari Rautio,
Plexpress, Helsinki, Finland; John Londesborough, VTT, Espoo, Finland
ABSTRACT: The hybrid Saccharomyces pastorianus genome consists of two diverged genomes believed to be those of S. cerevisiae and the recently discovered S. eubayanus.
To clarify the functional relationship between these sub-genomes and
its contribution to fermentation performance, molecular probes were
designed to monitor differential transcription of S. cerevisiae- and S. eubayanus-type genes of S. pastorianus
under different fermentation conditions. The TRAC (transcriptional
profiling with the aid of affinity capture) system was used, as it has
the advantage of allowing reliable differentiation of orthologous genes
in large numbers of samples (10 samples were taken in the first 24 hr).
Samples were taken from 2-L, 15°P, all-malt wort fermentations conducted
at different temperatures (10–20°C), and the TRAC system was used to
monitor the expression of genes involved in sugar import, including MAL×1 (maltose transport) and MAL×2 (alpha-glucosidase). Sugar transport is known to be strongly temperature-dependent. As expected, peak expression of MAL×1 and MAL×2, both the S. cerevisiae and S. eubayanus
versions, occurred later in fermentations at lower temperatures. It
also lasted longer (about 2 days at 10°C compared to half a day at
20°C). Unexpectedly, the S. cerevisiae MAL×1 and MAL×2 genes were activated clearly (up to 12 hr) before their S. eubayanus versions. The results give insight into the independence and inter-dependence of the S. cerevisiae and S. eubayanus sub-genomes in S. pastorianus.
The different timing of responses may have practical importance
regarding monitoring of yeast activity during fermentation. Results are
discussed in relation to the activity of other orthologous genes in S. pastorianus, including MAL×3 (MAL activation), AGT1 (alpha-glucoside transport), and HXT genes responsible for high or low affinity glucose transport.
Gibson was awarded a Ph.D. degree from University College Dublin,
Ireland, in 2004, where he had specialized in fungal stress responses.
On completion of his studies he joined the brewing science research
group at Oxford Brookes University and later at Nottingham University,
England, where his research covered a range of subjects, including
brewing yeast stress responses, yeast transcriptomics during industrial
fermentation, genetic stability of brewing yeast, and molecular
identification of brewery contaminants. Since 2009 he has been employed
as a senior scientist and project manager at VTT, Finland, with
responsibility for yeast physiology and fermentation research.