A story was making small rounds on the internet recently about engineering yeast to produce wine that eludes the joy of hangovers. The press release of it can be found here. If you go to the original research paper, which is here, you’d find something that might seem a bit technical and has little to do with hangovers. So, what gives?
Well, some of the stories making the rounds have stretched the information in the press release a bit. Appropriately, an egregious example came from the Daily Mail, whose bold bullet point proclaimed “Scientists have isolated gene responsible for hangovers.” This is patently untrue. What the author of the press release did was present a prospective impact of the work in addition to the work itself. So what was the work?
The paper by Zhang et al. described the construction of a “quadruple auxotrophic strain of polyploid yeast.” A polyploid yeast is one that contains many copies of its genome. Humans have two copies of our genome, making us diploid. Watermelon is triploid, with three copies. Yeast, on the other hand, can exist with one, two, or more copies (polyploid) of their genome.
This is, in fact, one of yeast’s attractive features to biologists. The most common yeast model organism in research is Saccharomyces cerevisiae, a.k.a. baker’s/brewer’s yeast. Its natural life cycle includes haploid and diploid stages. Though most of the ones living in the wild spend most of their time as diploids, in laboratories they are more commonly kept as haploids. This makes them easy to manipulate and can simplify experiments.
Yeast is a powerful system for research because of this ease of genetic manipulation, a basic tool of which is genetic markers. A common marker is “auxotrophy.” Yeast is able to make a number of nutrients (such as amino acid) essential for living. When genes responsible for synthesis of these nutrients are disabled in a strain, it becomes auxotrophic for those nutrients and requires supplements to survive. Thus, biologists can make desired modifications in specific auxotrophic strains and subsequently track and identify them using the auxotrophic markers.
However, constructing auxotrophic strains in anything but a haploid can be challenging. This is because in strains with more than one copy of the genome, the set of genes required to synthesize a particular nutrient exists in more than one copy. In polyploid yeast, disabling such genes using traditional methods is a laborious nightmare. However, an elegant potential solution emerged recently called “CRISPR.” In a nutshell, this is a bacterial immune system-turned-technology to perform genetic modifications with high specificity and efficiency.
But why would you want to mess around with polyploid yeast, especially if laboratory haploids are easy to manipulate? Turns out, many yeast strains in industrial applications are polyploid. (And yeast is highly prevalent in industry, from food and drinks to pharmaceuticals to fuel, etc.) The ability to better manipulate polyploid yeast is certainly of value. Zhang et al. demonstrated how CRISPR can be used to engineer auxotrophic markers into polyploids. They specifically made a quadruple auxotrophic strain, with synthesis pathways for four nutrients disabled.
This is very cool, showcasing CRISPR as a new—and ostensibly better, at least in some ways,—tool to perform an old task. What this study did not do, however, is produce a hangover-free wine. For sure, a better method to modify polyploid yeast makes it easier to further study and tailor industrial yeast strains to their tasks. This could mean ultimately identifying genes responsible for certain characteristics in the final products, such as taste of wine or amount of undesirable byproducts in it. After that, one could build designer strains in order to produce the “perfect” wine.
But that is all in the future. On top of that, a product like wine is so complex—in terms of the compounds in it and the ingredients and reactions involved in its production—eliminating something like the culprit of hangover may involve more than simply a set of genes in the fermenting organism. Anyhow, that’s somewhat beside the point here. The point is misreporting.
As you can see, there is a disconnect between the original study and some news articles that stemmed from it. Sure, the press release from the University of Illinois, where the study took place, may have spun the impact and potential applications of the study. But the citation to the paper is there. Any reporter from a newspaper should at least read and understand the abstract and report on the story, not just drink the press release kool-aid and play telephone. Reporters like that are spreading their own scientific illiteracy and doing a disservice to the public. Or, worse yet, maybe it was written by a robot.
-Dave Yuan
“Construction of a quadruple auxotrophic mutant of an industrial polyploid Saccharomyces cerevisiae using RNA-guided Cas9 nuclease” by Guochang Zhang, In Iok Kong, Heejin Kim, Jingjing Liu, Jamie H.D. Cate, and Yong-Su Jin. Applied and Environmental Microbiology (2014) doi:10.1128/AEM.02310-14
