Scimex: Vineyards producing high-quality 'classic' wines may owe their success
to the local bacteria rather than soil chemistry, argue the authors of
new US-led research. The scientists compared microbes growing on
grapevines and in the soil of Merlot vineyards in New York, Californian
and Bordeaux, and found the same types of beneficial bacteria in all
three locations - suggesting that it is not so much the chemical makeup
of soil that affects wine quality, but the bacteria in vineyards.
In the first study of an entire wine grapevine's microbiome,
researchers have found that the microbes associated with the grapes,
leaves and flowers are largely derived from the soil microbes found
around the plant's roots. The findings, published in mBio the
online open-access journal of the American Society for Microbiology,
could help dissect how microbes affect a wine's properties and pave the
way for biotechnological advances for producing hardier crops.
"Growers
have been sub-selecting the best regions to grow grapes over thousands
of years, but the science of that is poorly understood," says Jack
Gilbert, a microbial ecologist at the Argonne National Laboratory in
Illinois. "Just the same as the human biome plays a role in health,
bacteria have intricate associations with plants that affect disease
resistance, stress tolerance and productivity."
Besides making
tasty wine, Merlot grapes, Gilbert explains, are a really well
controlled, understood crop system. He and his colleagues wanted to
understand how different bacteria colonize these plants and also how
those microbes might ultimately contribute to the wine's sensory
properties. In other words, they wanted to find out if there is a
microbiological component of terroir--the wine's properties that are
imparted by the ground its grapes are grown in.
The team of
researchers, which included winemaker Gilles Martin, looked at four
closely related Merlot plants growing in five different vineyards across
a 2-mile stretch of the North Fork region of Long Island, New York. For
each location, they sampled the soil, roots, leaves, flowers and grapes
throughout a growing season. Then, the team used shotgun metagenomic
sequencing to characterize all the bacterial species found on each part
of the grapevine. The team found that it's all about location, location,
location.
"Where you grow that particular grapevine is the most
important characteristic shaping which bacteria will colonize the
plant," says Gilbert. The majority of bacterial species found in the
plant were also present in the soil it was growing in. A few rare
species found in the soil, were enriched in the aboveground grapes and
leaves. This indicates that the soil acts as a reservoir for most of the
bacteria that are colonizing the plants' structures.
Next, the
team compared the New York grapes' microbiome to those associated with
Merlot grapes from Bordeaux, France, and crushed Merlot grapes from
California. All three hosted similar bacteria species. "No matter where
you are in the world, the types of bacteria growing on or in Merlot
grapes are quite similar," says Gilbert.
There is immense
commercial interest in finding specific bacteria that would add benefits
to crops, such as drought and pest resistance. But the findings may
also point to new, bacterial ways to massage a wine's outcome.
"From
the wine industry's perspective, terroir comes from the plant's
physiology, the chemical nature of the grapes, and the yeast that do the
fermenting work," says Gilbert. From this study, Gilbert argues that
the microbes present in the soil, rather than the soil's physical
characteristics, might play a bigger role in influencing terroir.
"We
don't have evidence that bacteria are specifically contributing to
terroir, but our next step is to figure out how those bacteria are
affecting the chemistry of the plant."