As I’ve mentioned previously in many past posts (e.g. here, here and here), I’m working with and researching the properties of newly created lager yeast hybrids (for my PhD project). In the linked posts, you can read about some of our initial results from the project. These mainly established the technique and showed that de novo lager hybrids can exhibit hybrid vigor over their parent strains. Since then I’ve been looking more closely at how hybrids made from the same parent strains, but with varying ploidy levels (i.e. chromosome numbers), behave in regards to fermentation performance, aroma compound production and stress tolerance. We had some very interesting results, and we saw (at least with our hybrids) that the hybrids with higher ploidy level performed better and produced more aroma-rich beer. In order to try to understand why, we sequenced the hybrids and performed transcriptional analysis on selected genes. We saw that the higher ploidy hybrids had higher copy numbers of several genes related to aroma synthesis, and these were also transcribed at higher levels during fermentation. I held a presentation about this research at the 5th International Young Scientists Symposium on Malting, Brewing and Distilling in Chico about a month ago. You can download the presentation slides below! I’m also very happy to announce that we recently had a manuscript on this work accepted for publication in Applied Microbiology and Biotechnology. ‘Ploidy influences the functional attributes of de novo lager yeast hybrids‘ was just published online, and you can find a link to the publication below as well (it is Open Access!).
Link to the publication: http://link.springer.com/article/10.1007/s00253-016-7588-3
Link to the presentation slides: http://beer.suregork.com/wp-content/uploads/2016/04/Krogerus_YSS2016.pdf
The genomes of hybrid organisms, such as lager yeast (Saccharomyces cerevisiae × Saccharomyces eubayanus), contain orthologous genes, the functionality and effect of which may differ depending on their origin and copy number. How the parental subgenomes in lager yeast contribute to important phenotypic traits such as fermentation performance, aroma production, and stress tolerance remains poorly understood. Here, three de novo lager yeast hybrids with different ploidy levels (allodiploid, allotriploid, and allotetraploid) were generated through hybridization techniques without genetic modification. The hybrids were characterized in fermentations of both high gravity wort (15 °P) and very high gravity wort (25 °P), which were monitored for aroma compound and sugar concentrations. The hybrid strains with higher DNA content performed better during fermentation and produced higher concentrations of flavor-active esters in both worts. The hybrid strains also outperformed both the parent strains. Genome sequencing revealed that several genes related to the formation of flavor-active esters (ATF1, ATF2¸ EHT1, EEB1, and BAT1) were present in higher copy numbers in the higher ploidy hybrid strains. A direct relationship between gene copy number and transcript level was also observed. The measured ester concentrations and transcript levels also suggest that the functionality of the S. cerevisiae– and S. eubayanus-derived gene products differs. The results contribute to our understanding of the complex molecular mechanisms that determine phenotypes in lager yeast hybrids and are expected to facilitate targeted strain development through interspecific hybridization.