I feel bad for again having to start off a post by apologizing for my inactivity here at the blog. It has been quite a busy summer for me, as my wife and I got our first child (his name is Ludwig) in the end of June. I’m currently on parental leave from my research work, so have also been busy with wrapping up my ongoing work, so I can continue with it when I return from my leave in March. Anyways, we have been working on lots of interesting hybrid-related projects at our lab, so I thought I’d briefly sum up some of the topics we’ve been working on:
Adaptive evolution of newly created lager hybrids
This is the project I’ve been dedicating most of my time to the past 18 months. While the results haven’t been published in a peer-reviewed journal yet, we’ve submitted a manuscript based on the results for review, and have uploaded a pre-print to bioRxiv for everyone to read. We and others before us, have noticed that many hybrids (particularly interspecies ones) tend to have quite unstable genomes. This means that their genomes, along with their phenotypic properties, can change as the hybrid is grown for several generations. This is not very desirable in a brewing environment, where yeast is reused for multiple consecutive fermentations. We decided to exploit this instability, by growing (and adapting) some of our hybrids in media containing high ethanol concentrations for 130+ generations. We isolated colonies of variant strains along the adaptation process, and through a screening step, we managed to select several variant strains that outperformed the original hybrids in wort fermentations. Many of these variants also had higher ethanol tolerance than the original hybrids, and produced a more desirable aroma profile (more esters, less higher alcohols, and less diacetyl). We sequenced the genomes of these variants, and noticed that all variants had undergone gains and losses of various chromosomes. The results seemed to suggest that the S. cerevisiae sub-genome in the hybrids was ‘preferred’, while the S. eubayanus sub-genome had undergone more losses. We also identified multiple single nucleotide polymorphisms and small indels which affected the coding sequence of many genes. Mutations in some of these genes had previously been reported to affect ethanol tolerance and general fitness. In addition, these variant strains appeared stable when grown for multiple generations. All in all, our study shows that interspecific hybridization, coupled with adaptive evolution, is a powerful tool for producing new strains with tailor-designed properties.
Here is a link to the pre-print: https://www.biorxiv.org/content/early/2017/10/16/204198
Alternative Saccharomyces interspecific hybrid combinations for lager fermentations
This is a project a MSc student, Jarkko Nikulin, worked on last year. We wanted to investigate whether S. eubayanus really is that important for lager (i.e. low-temperature) fermentations. Studies have shown that there are several other cold-tolerant Saccharomyces species (though not as cold-tolerant as S. eubayanus), and the questions was: can we replace S. eubayanus in a lager hybrid with one of these alternative Saccharomyces species? We generated a range of S. cerevisiae × (S. arboricola / S. eubayanus / S. mikatae / S. uvarum) hybrids and compared them in wort fermentations. We noticed that S. eubayanus seems to be dispensable, as many of the other alternative hybrids performed just as well in low-temperature wort fermentations. There is a quite a lot of potential to generate some really diverse and unique strains using these alternative Saccharomyces species.
Here is a link to the study: http://onlinelibrary.wiley.com/doi/10.1002/yea.3246/full/
The use of Saccharomyces eubayanus and its hybrids in wine-making
This is a project my colleague and fellow PhD student Frederico Magalhaes has been working on. In his PhD project he has been looking at the use of S. eubayanus for cider and wine-making. Many wine fermentations are carried out at lower temperatures, e.g. to increase aromatic complexity and decrease the growth of contaminants, and the use of S. eubayanus would allow for that. You can read more about Frederico’s work in the following blog post:
Here is also a link to a published study: https://doi.org/10.1093/femsyr/fox049
Review on modern yeast development strategies
Finally, here is a review on modern brewing yeast design and development that I was involved in, and was written for the ISSY33 conference that took place this summer in Ireland. Some of the topics that are covered are non-conventional brewing yeast, hybridization and genome analysis.
Here is a link to the review: https://academic.oup.com/femsyr/article/17/4/fox038/3861261
Very cool writeup. One question for you – when you say yeast were adapted for “130+ generations”, does this mean an estimated 130 cell divisions, or 130 passages (with each passage presumably containing many generations).
Thanks for the comment Bryan! Generations in this case means the estimated number of cell divisions. We performed 30 consecutive batch fermentations with each strain in media containing an initial EtOH concentration of 10% (v/v).