Sub-genomic cooperation in the hybrid lager yeast Saccharomyces pastorianus

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.

Brian 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.