Could fruit flies be responsible for the nice smell of most wines? This is a really interesting idea suggested by a research paper just published in scientific journal Ecology Letters. It’s by a New Zealand group, led by Dr Mat Goddard, who have already published some really interesting research on yeast ecology, showing that the wild yeasts completing fermentations in a number of New Zealand regions are local to the vineyard sites, and not escaped commercial strains resident in the winery. The lead author on the paper is Dr Claudia Buser, a postdoctoral researcher in Goddard’s lab.
The authors are looking at the broader ecological idea that niche construction can initiate the evolution of mutualistic interactions, but this work has relevance for wine. What is niche construction? Saccharomyces cerevisiae, the wine yeast, helps to construct an environment that suits it. It likes ripe fruit as a food source, but so do many other organisms. So S. cerevisiae uses alcoholic fermentation, which is a really inefficient way of using the sugar up, but which creates heat and alcohol that makes it a much less inviting environment for others. In particular, bacteria don’t tolerate alcohol the way that this yeast is able to.
But ripe fruits are quite seasonal, and spread far apart, and yeasts have a problem: how do they get to them, considering they are not mobile? The strategy they have evolved is to hitch a ride on insects, and in particular, fruit flies. These flies are attracted to fermenting fruit where yeasts are growing, and they lay their eggs there.
And this study shows that yeasts are actively producing aromatic compounds to lure the flies.
This has answered a question that previously had confused scientists. Why do yeasts go to the bother of producing all these aromatic compounds that we find in wine, when there is an energetic cost involved to them, and seemingly no benefit? It seems that the yeasts benefit because the aromas bring in their ride.
And the flies? They benefit too, because fermenting fruit is a fertile environment for them to lay their eggs in. It seems that the eggs laid in fruit with S. cerevisiae present do better. The most attractive smelling yeasts lure more fruit flies, and both dispersal and egg fertility are both enhanced. This is known in biology as a mutualistic symbiosis.
In the experiments Goddard’s lab undertook, flies were released into a glass tube maze where they could choose among different types of yeast, and these results were replicated in the field, which demonstrated that S. cerevisiae was being carried by 100 times more flies than you’d expect if the flies were randomly recruiting fungi from the environment.
So this raises the strong possibility that we have flies to thank for many of the pleasing aromas of the wines we drink.