Adapting a Photochemical Reactor to the Study of UV Ecology in Vineyard Yeast

In the vineyard, many genera of yeast can be present on the grapes, but they are eventually outcompeted by Saccharomyces yeast as fermentation progresses. A selective pressure that has the potential to affect the composition of the non-Saccharomyces community is UV light, particularly in places with very high levels of UV-B (280 to 315 nm) radiation, like New Zealand. Understanding this ecology could conceivably be very important because of growing evidence that non-Saccharomyces yeast present on grapes in vineyards can play a role in the fermentation process and terroir. Thus, understanding how UV light can affect yeast community composition represents a step toward understanding how specific taste signatures derived from certain microbial communities are produced. To fully understand these processes, overall UV sensitivity to wavelengths encountered in the vineyard would need to be characterized for each member of the non-Saccharomyces vineyard yeast community. Problematically, traditional UV-sensitivity assays have used instruments that only emit at 254 nm (UV-C), a wavelength filtered out by the ozone layer in natural environments. Here, we present a method that allows experimental determination of UV-B sensitivity in yeast (and presumably, sensitivity to several other wavelengths) that uses a Rayonet RPR-100 photochemical reactor. This method outperforms traditional methods of irradiation in both ecological relevance and tight control of wavelength and flux. With our protocol, better understanding of the ecological processes that drive community structure in vineyards, and therefore also microbial terroir, can be achieved.