A2: Microbes in the News

Article Title: Microbial biogeography of wine grapes is conditioned by cultivar, vintage, and climate

Date: September 16, 2013

Author: Nicholas Bokulich, John Thorngate, Paul Richardson, David Mills

Source: Proceedings of the National Academy of Sciences of the USA

Link: https://www.pnas.org/content/111/1/E139.full

Summary: This was a study done on wine! The researchers collected 235 samples of grape must (the crushed de-stemmed berries right before fermentation) from 8 different wineries in 4 California wine regions. They took DNA samples from all these grapes and sequenced specific genetic markers for bacteria and fungi instead of the entire genome. They found that a lot of factors make microbial differences, especially the region (geographic location) the grape was harvested from. The relative humidity and total precipitation of each area influences the specific niche for bacteria and fungi. The microbes found in a Cabernet Sauvignon from the Napa/Sonoma valley are completely different from grapes harvested from the central coast microbes. One example given was Zinfandel, which grape has thin skins leading to more berry breakage, these grapes carry more Gluconbacter and Lactobacillales which are commonly found on damaged fruits. This in turn, of course, leads to different flavors. For example, Oenococcus oeni carries out malolactic fermentation which adds a buttery flavor and reduces the acidity of the wine (think, Chardonnay) and Brettanomyces which adds a bit of a bitter bite and can sometimes spoil the wine (corked).

Connection: The authors talk about how microbes can be transferred in a modular way, by horizontal gene transfer, which we have covered in class. They go into detail about genome sequencing and online databases to help decipher sequences that are in the millions. They also briefly touch on fermentation.

Critical Analysis: I love wine, so this article was very appealing to me. I know the basic process of how wine is fermented and I know about different grapes and regions, but I never really thought about the microbes in different areas and in different wines and how they can affect them. I thought this study was really interesting in how environmental factors influence microbial populations and how it may be possible to predict how it can change with global climate change. Growers in the vineyards may be able to make changes to those conditions each year after tastings to be rid of anything that is undesirable or enhance things that are positive. I knew winemaking was an art in itself, but I’m fascinated to see how much science actually plays a part in the sometimes pretentious lifestyle.

Question: Will there ever be a wine that doesn’t cause a hangover!? 🙂 Just kidding. I’m wondering about the microbes in the soil and how they affect vine growth. There are microbes in the grapes themselves, but do the microbes in the soil play a part in taste at all? Or does that specifically reside on the personal palate of each individual person.